This is netcdf-c.info, produced by makeinfo version 4.12 from /machine/netcdf/nc_test_7752/man4//defines.texi. Copyright (C) 2005-2009 University Corporation for Atmospheric Research Permission is granted to make and distribute verbatim copies of this manual provided that the copyright notice and these paragraphs are preserved on all copies. The software and any accompanying written materials are provided "as is" without warranty of any kind. UCAR expressly disclaims all warranties of any kind, either expressed or implied, including but not limited to the implied warranties of merchantability and fitness for a particular purpose. The Unidata Program Center is managed by the University Corporation for Atmospheric Research and sponsored by the National Science Foundation. Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the views of the National Science Foundation. Mention of any commercial company or product in this document does not constitute an endorsement by the Unidata Program Center. Unidata does not authorize any use of information from this publication for advertising or publicity purposes. INFO-DIR-SECTION netCDF scientific data format START-INFO-DIR-ENTRY * netcdf-c: (netcdf-c). The NetCDF C Interface Guide END-INFO-DIR-ENTRY  File: netcdf-c.info, Node: Top, Next: Use of the NetCDF Library, Prev: (dir), Up: (dir) The NetCDF C Interface Guide **************************** This document describes the C interface to the netCDF library; it applies to netCDF version 4.1.1 and was last updated on 31 January 2010. For a complete description of the netCDF format and utilities see *note The NetCDF Users Guide: (netcdf)Top. * Menu: * Use of the NetCDF Library:: * Datasets:: * Groups:: * Dimensions:: * User Defined Data Types:: * Variables:: * Attributes:: * Summary of C Interface:: * NetCDF 3 Transition Guide:: * NetCDF 2 C Transition Guide:: * NetCDF-3 Error Codes:: * NetCDF-4 Error Codes:: * DAP Error Codes:: * Combined Index:: --- The Detailed Node Listing --- Use of the NetCDF Library * Creating:: Creating a NetCDF Dataset * Reading Known :: Reading a NetCDF Dataset with Known Names * Reading Unknown :: Reading a netCDF Dataset with Unknown Names * Adding:: Adding New Dimensions, Variables, Attributes * Errors:: Error Handling * Compiling:: Compiling and Linking with the NetCDF Library Datasets * Interface Descriptions:: What's in the Function Documentation * parallel access:: * nc_strerror:: Get Error Messages * nc_inq_libvers:: Get netCDF library version * nc_create:: Create a Dataset * nc__create:: Create a Dataset with Performance Tuning * nc_create_par:: * nc_open:: Open a Dataset * nc__open:: Open a Dataset with Performance Tuning * nc_open_par:: * nc_redef:: Put a Dataset into Define Mode * nc_enddef:: Leave Define Mode * nc__enddef:: Leave Define Mode with Performance Tuning * nc_close:: Close a Dataset * nc_inq Family:: Inquire about a Dataset * nc_sync:: Synchronize a Dataset to Disk * nc_abort:: Back Out of Recent Definitions * nc_set_fill:: Set Fill Mode for Writes * nc_set_default_format:: Change the default output format * nc_set_chunk_cache:: * nc_get_chunk_cache:: Groups * nc_inq_ncid:: * nc_inq_grps:: * nc_inq_varids:: * nc_inq_dimids:: * nc_inq_grpname:: * nc_inq_grpname_full:: * nc_inq_grpname_len:: * nc_inq_grp_parent:: * nc_inq_grp_ncid:: * nc_inq_grp_full_ncid:: * nc_def_grp:: Dimensions * Dimensions Introduction:: * nc_def_dim:: Create a Dimension * nc_inq_dimid:: Get a Dimension ID from Its Name * nc_inq_dim Family:: Inquire about a Dimension * nc_rename_dim:: Rename a Dimension * nc_inq_unlimdims:: User Defined Data Types * User Defined Types:: * nc_inq_typeids:: * nc_inq_typeid:: * nc_inq_type:: * nc_inq_user_type:: * Compound Types:: * nc_def_compound:: * nc_insert_compound:: * nc_insert_array_compound:: * nc_inq_compound:: * nc_inq_compound_name:: * nc_inq_compound_size:: * nc_inq_compound_nfields:: * nc_inq_compound_field:: * nc_inq_compound_fieldname:: * nc_inq_compound_fieldindex:: * nc_inq_compound_fieldoffset:: * nc_inq_compound_fieldtype:: * nc_inq_compound_fieldndims:: * nc_inq_compound_fielddim_sizes:: * Variable Length Array:: * nc_def_vlen:: * nc_inq_vlen:: * nc_free_vlen:: * nc_free_vlens:: * Opaque Type:: * nc_def_opaque:: * nc_inq_opaque:: * Enum Type:: * nc_def_enum:: * nc_insert_enum:: * nc_inq_enum:: * nc_inq_enum_member:: * nc_inq_enum_ident:: Compound Types Introduction * nc_def_compound:: * nc_insert_compound:: * nc_inq_compound:: * nc_inq_compound_fieldname:: * nc_inq_compound_fieldindex:: * nc_inq_compound_fieldoffset:: * nc_inq_compound_fieldtype:: Variables * Variable Introduction:: * Variable Types:: * NetCDF-3 Variable Types:: * NetCDF-4 Atomic Types:: * nc_def_var:: Create a Variable * nc_def_var_chunking:: Set chunking parameters * nc_inq_var_chunking:: Learn about chunking parameters * nc_set_var_chunk_cache:: * nc_get_var_chunk_cache:: * nc_def_var_fill:: * nc_inq_var_fill:: * nc_def_var_deflate:: Set compression parameters * nc_inq_var_deflate:: Learn about compression parameters * nc_inq_var_szip:: * nc_def_var_fletcher32:: Set checksum filter * nc_inq_var_fletcher32:: Learn if checksum filter is set * nc_def_var_endian:: * nc_inq_var_endian:: * nc_inq_varid:: Get a Variable ID from Its Name * nc_inq_var:: Get Information about a Variable from Its ID * nc_put_var1_ type:: Write a Single Data Value * nc_put_var_ type:: Write an Entire Variable * nc_put_vara_ type:: Write an Array of Values * nc_put_vars_ type:: Write a Subsampled Array of Values * nc_put_varm_ type:: Write a Mapped Array of Values * nc_get_var1_ type:: Read a Single Data Value * nc_get_var_ type:: Read an Entire Variable * nc_get_vara_ type:: Read an Array of Values * nc_get_vars_ type:: Read a Subsampled Array of Values * nc_get_varm_ type:: Read a Mapped Array of Values * Strings:: Reading and Writing Character String Values * nc_free_string:: * Fill Values:: What's Written Where there's No Data? * nc_rename_var:: Rename a Variable * nc_copy_var:: * nc_var_par_access:: Reading and Writing Character String Values * Classic Strings:: * Arrays of Strings:: Attributes * Attributes Introduction:: * nc_put_att_ type:: * nc_inq_att Family:: * nc_get_att_ type:: * nc_copy_att:: * nc_rename_att:: * nc_del_att::  File: netcdf-c.info, Node: Use of the NetCDF Library, Next: Datasets, Prev: Top, Up: Top 1 Use of the NetCDF Library *************************** You can use the netCDF library without knowing about all of the netCDF interface. If you are creating a netCDF dataset, only a handful of routines are required to define the necessary dimensions, variables, and attributes, and to write the data to the netCDF dataset. (Even less is needed if you use the ncgen utility to create the dataset before running a program using netCDF library calls to write data.) Similarly, if you are writing software to access data stored in a particular netCDF object, only a small subset of the netCDF library is required to open the netCDF dataset and access the data. Authors of generic applications that access arbitrary netCDF datasets need to be familiar with more of the netCDF library. In this chapter we provide templates of common sequences of netCDF calls needed for common uses. For clarity we present only the names of routines; omit declarations and error checking; omit the type-specific suffixes of routine names for variables and attributes; indent statements that are typically invoked multiple times; and use ... to represent arbitrary sequences of other statements. Full parameter lists are described in later chapters. * Menu: * Creating:: Creating a NetCDF Dataset * Reading Known :: Reading a NetCDF Dataset with Known Names * Reading Unknown :: Reading a netCDF Dataset with Unknown Names * Adding:: Adding New Dimensions, Variables, Attributes * Errors:: Error Handling * Compiling:: Compiling and Linking with the NetCDF Library  File: netcdf-c.info, Node: Creating, Next: Reading Known, Prev: Use of the NetCDF Library, Up: Use of the NetCDF Library 1.1 Creating a NetCDF Dataset ============================= Here is a typical sequence of netCDF calls used to create a new netCDF dataset: nc_create /* create netCDF dataset: enter define mode */ ... nc_def_dim /* define dimensions: from name and length */ ... nc_def_var /* define variables: from name, type, ... */ ... nc_put_att /* put attribute: assign attribute values */ ... nc_enddef /* end definitions: leave define mode */ ... nc_put_var /* provide values for variables */ ... nc_close /* close: save new netCDF dataset */ Only one call is needed to create a netCDF dataset, at which point you will be in the first of two netCDF modes. When accessing an open netCDF dataset, it is either in define mode or data mode. In define mode, you can create dimensions, variables, and new attributes, but you cannot read or write variable data. In data mode, you can access data and change existing attributes, but you are not permitted to create new dimensions, variables, or attributes. One call to nc_def_dim is needed for each dimension created. Similarly, one call to nc_def_var is needed for each variable creation, and one call to a member of the nc_put_att family is needed for each attribute defined and assigned a value. To leave define mode and enter data mode, call nc_enddef. Once in data mode, you can add new data to variables, change old values, and change values of existing attributes (so long as the attribute changes do not require more storage space). Single values may be written to a netCDF variable with one of the members of the nc_put_var1 family, depending on what type of data you have to write. All the values of a variable may be written at once with one of the members of the nc_put_var family. Arrays or array cross-sections of a variable may be written using members of the nc_put_vara family. Subsampled array sections may be written using members of the nc_put_vars family. Mapped array sections may be written using members of the nc_put_varm family. (Subsampled and mapped access are general forms of data access that are explained later.) Finally, you should explicitly close all netCDF datasets that have been opened for writing by calling nc_close. By default, access to the file system is buffered by the netCDF library. If a program terminates abnormally with netCDF datasets open for writing, your most recent modifications may be lost. This default buffering of data is disabled by setting the NC_SHARE flag when opening the dataset. But even if this flag is set, changes to attribute values or changes made in define mode are not written out until nc_sync or nc_close is called.  File: netcdf-c.info, Node: Reading Known, Next: Reading Unknown, Prev: Creating, Up: Use of the NetCDF Library 1.2 Reading a NetCDF Dataset with Known Names ============================================= Here we consider the case where you know the names of not only the netCDF datasets, but also the names of their dimensions, variables, and attributes. (Otherwise you would have to do "inquire" calls.) The order of typical C calls to read data from those variables in a netCDF dataset is: nc_open /* open existing netCDF dataset */ ... nc_inq_dimid /* get dimension IDs */ ... nc_inq_varid /* get variable IDs */ ... nc_get_att /* get attribute values */ ... nc_get_var /* get values of variables */ ... nc_close /* close netCDF dataset */ First, a single call opens the netCDF dataset, given the dataset name, and returns a netCDF ID that is used to refer to the open netCDF dataset in all subsequent calls. Next, a call to nc_inq_dimid for each dimension of interest gets the dimension ID from the dimension name. Similarly, each required variable ID is determined from its name by a call to nc_inq_varid Once variable IDs are known, variable attribute values can be retrieved using the netCDF ID, the variable ID, and the desired attribute name as input to a member of the nc_get_att family (typically nc_get_att_text or nc_get_att_double) for each desired attribute. Variable data values can be directly accessed from the netCDF dataset with calls to members of the nc_get_var1 family for single values, the nc_get_var family for entire variables, or various other members of the nc_get_vara, nc_get_vars, or nc_get_varm families for array, subsampled or mapped access. Finally, the netCDF dataset is closed with nc_close. There is no need to close a dataset open only for reading.  File: netcdf-c.info, Node: Reading Unknown, Next: Adding, Prev: Reading Known, Up: Use of the NetCDF Library 1.3 Reading a netCDF Dataset with Unknown Names =============================================== It is possible to write programs (e.g., generic software) which do such things as processing every variable, without needing to know in advance the names of these variables. Similarly, the names of dimensions and attributes may be unknown. Names and other information about netCDF objects may be obtained from netCDF datasets by calling inquire functions. These return information about a whole netCDF dataset, a dimension, a variable, or an attribute. The following template illustrates how they are used: nc_open /* open existing netCDF dataset */ ... nc_inq /* find out what is in it */ ... nc_inq_dim /* get dimension names, lengths */ ... nc_inq_var /* get variable names, types, shapes */ ... nc_inq_attname /* get attribute names */ ... nc_inq_att /* get attribute types and lengths */ ... nc_get_att /* get attribute values */ ... nc_get_var /* get values of variables */ ... nc_close /* close netCDF dataset */ As in the previous example, a single call opens the existing netCDF dataset, returning a netCDF ID. This netCDF ID is given to the nc_inq routine, which returns the number of dimensions, the number of variables, the number of global attributes, and the ID of the unlimited dimension, if there is one. All the inquire functions are inexpensive to use and require no I/O, since the information they provide is stored in memory when a netCDF dataset is first opened. Dimension IDs use consecutive integers, beginning at 0. Also dimensions, once created, cannot be deleted. Therefore, knowing the number of dimension IDs in a netCDF dataset means knowing all the dimension IDs: they are the integers 0, 1, 2, ...up to the number of dimensions. For each dimension ID, a call to the inquire function nc_inq_dim returns the dimension name and length. Variable IDs are also assigned from consecutive integers 0, 1, 2, ... up to the number of variables. These can be used in nc_inq_var calls to find out the names, types, shapes, and the number of attributes assigned to each variable. Once the number of attributes for a variable is known, successive calls to nc_inq_attname return the name for each attribute given the netCDF ID, variable ID, and attribute number. Armed with the attribute name, a call to nc_inq_att returns its type and length. Given the type and length, you can allocate enough space to hold the attribute values. Then a call to a member of the nc_get_att family returns the attribute values. Once the IDs and shapes of netCDF variables are known, data values can be accessed by calling a member of the nc_get_var1 family for single values, or members of the nc_get_var, nc_get_vara, nc_get_vars, or nc_get_varm for various kinds of array access.  File: netcdf-c.info, Node: Adding, Next: Errors, Prev: Reading Unknown, Up: Use of the NetCDF Library 1.4 Adding New Dimensions, Variables, Attributes ================================================ An existing netCDF dataset can be extensively altered. New dimensions, variables, and attributes can be added or existing ones renamed, and existing attributes can be deleted. Existing dimensions, variables, and attributes can be renamed. The following code template lists a typical sequence of calls to add new netCDF components to an existing dataset: nc_open /* open existing netCDF dataset */ ... nc_redef /* put it into define mode */ ... nc_def_dim /* define additional dimensions (if any) */ ... nc_def_var /* define additional variables (if any) */ ... nc_put_att /* define additional attributes (if any) */ ... nc_enddef /* check definitions, leave define mode */ ... nc_put_var /* provide values for new variables */ ... nc_close /* close netCDF dataset */ A netCDF dataset is first opened by the nc_open call. This call puts the open dataset in data mode, which means existing data values can be accessed and changed, existing attributes can be changed (so long as they do not grow), but nothing can be added. To add new netCDF dimensions, variables, or attributes you must enter define mode, by calling nc_redef. In define mode, call nc_def_dim to define new dimensions, nc_def_var to define new variables, and a member of the nc_put_att family to assign new attributes to variables or enlarge old attributes. You can leave define mode and reenter data mode, checking all the new definitions for consistency and committing the changes to disk, by calling nc_enddef. If you do not wish to reenter data mode, just call nc_close, which will have the effect of first calling nc_enddef. Until the nc_enddef call, you may back out of all the redefinitions made in define mode and restore the previous state of the netCDF dataset by calling nc_abort. You may also use the nc_abort call to restore the netCDF dataset to a consistent state if the call to nc_enddef fails. If you have called nc_close from definition mode and the implied call to nc_enddef fails, nc_abort will automatically be called to close the netCDF dataset and leave it in its previous consistent state (before you entered define mode). For netCDF-4/HDF5 format files, define mode is still important, but the user does not have to called nc_enddef - it is called automatically when needed. It may also be called by the user. In netCDF-4/HDF5 files, there are some settings which can only be modified during the very first define mode of the file. For example the compression level of a variable may be set only after the nc_def_var call and before the next nc_enddef call, whether it is called by the user explicitly, or when the user tries to read or write some data. At most one process should have a netCDF dataset open for writing at one time. The library is designed to provide limited support for multiple concurrent readers with one writer, via disciplined use of the nc_sync function and the NC_SHARE flag. If a writer makes changes in define mode, such as the addition of new variables, dimensions, or attributes, some means external to the library is necessary to prevent readers from making concurrent accesses and to inform readers to call nc_sync before the next access.  File: netcdf-c.info, Node: Errors, Next: Compiling, Prev: Adding, Up: Use of the NetCDF Library 1.5 Error Handling ================== The netCDF library provides the facilities needed to handle errors in a flexible way. Each netCDF function returns an integer status value. If the returned status value indicates an error, you may handle it in any way desired, from printing an associated error message and exiting to ignoring the error indication and proceeding (not recommended!). For simplicity, the examples in this guide check the error status and call a separate function, handle_err(), to handle any errors. One possible definition of handle_err() can be found within the documentation of nc_strerror (*note nc_strerror::). The nc_strerror function is available to convert a returned integer error status into an error message string. Occasionally, low-level I/O errors may occur in a layer below the netCDF library. For example, if a write operation causes you to exceed disk quotas or to attempt to write to a device that is no longer available, you may get an error from a layer below the netCDF library, but the resulting write error will still be reflected in the returned status value.  File: netcdf-c.info, Node: Compiling, Prev: Errors, Up: Use of the NetCDF Library 1.6 Compiling and Linking with the NetCDF Library ================================================= Details of how to compile and link a program that uses the netCDF C or FORTRAN interfaces differ, depending on the operating system, the available compilers, where the netCDF library and include files are installed, and whether or not you are using shared libraries. Nevertheless, we provide here examples of how to compile and link a program that uses the netCDF library on a Unix platform, so that you can adjust these examples to fit your installation. Every C file that references netCDF functions or constants must contain an appropriate #include statement before the first such reference: #include Unless the netcdf.h file is installed in a standard directory where the C compiler always looks, you must use the -I option when invoking the compiler, to specify a directory where netcdf.h is installed, for example: cc -c -I/usr/local/netcdf/include myprogram.c Alternatively, you could specify an absolute path name in the #include statement, but then your program would not compile on another platform where netCDF is installed in a different location. Unless the netCDF library is installed in a standard directory where the linker always looks, you must use the -L and -l options to link an object file that uses the netCDF library. If the netCDF library was configured with the -enable-shared flag, and the operating system supports shared libraries, then it should be possible to link an application program using a relatively simple command. For example: cc -o myprogram myprogram.o -L/usr/local/netcdf/lib -lnetcdf It should be noted that on some operating systems, when using shared libraries, the application itself may need to be compiled using some form of PIC (position independent code) flag; the particular flag will depend on the C compiler used. You should try it first without any PIC flag, and if that fails, then check with the system administrator about the proper form of PIC flag to use. In addition, for some C compilers (e.g. Sun's cc compiler) it is necessary to specify runtime paths to the relevant libnetcdf.so. This can be accomplished in one of two ways. 1. Add the path to the directory containing libnetcdf.so to the LD_LIBRARY_PATH environment variable. This path is searched at runtime to locate any needed shared library. This might be accomplished, for example, by the following shell command (assuming that libnetcdf.so is in /usr/local/netcdf/lib). LD_LIBRARY_PATH="/usr/local/netcdf/lib:$LD_LIBRARY_PATH" export LD_LIBRARY_PATH 2. Set the so-called runtime path when the application is linked so that the absolute paths of all needed shared libraries is included in the application binary. For gcc under Linus, this is usually automatic. For C compilers on Solaris (and probably other operating systems) the runtime path must be specified at link time. The command in this case might look like this. cc -o myprogram myprogram.o -L/usr/local/netcdf/lib -lnetcdf -R/usr/local/netcdf/lib Note that the -R flag is also C compiler dependent. For gcc and Linux, for example, the specification is usually of this form. cc ... -Wl,-rpath,/usr/local/netcdf/lib Other compilers may use other flags to specify this. Check with the local system administrator. If shared libraries are not supported or are not being used for some reason, then it is necessary to include all the dependent libraries in the compile command. For example, for a netCDF-4 enabled library, it will be necessary to link with two HDF5 libraries, at least one compression library, and (on some systems) the math library. cc -o myprogram myprogram.o -L/usr/local/netcdf/lib -L/usr/local/hdf5/lib -lnetcdf -lhdf5_hl -lhdf5 -lz Other configuration features (e.g. DAP support or parallel IO) may require additional libraries. A complete list of necessary libraries can be obtained by executing the "nc-config -libs" command. For example: ./nc-config --libs might return something like this: -L/tmp/install/spock/lib -lnetcdf -L/upc/share/stdinstall/local/spock/lib -lhdf5_hl -lhdf5 -L/upc/share/stdinstall/local/spock/lib -lz -lm -L/upc/share/stdinstall/local/spock/lib -lcurl -L/usr/kerberos/lib64 -L/upc/share/stdinstall/local/spock/lib -lidn -lssl -lcrypto -lldap -lrt -lssl -lcrypto -ldl -lz -lz Obviously there is some redundancy in this list, so it can be reduced somewhat to produce this slightly simpler list. -L/tmp/install/spock/lib -lnetcdf -L/upc/share/stdinstall/local/spock/lib -lhdf5 -lhdf5_hl -lz -lcurl -L/usr/kerberos/lib64 -lcrypto -lssl -ldl -lidn -lldap -lm -lrt  File: netcdf-c.info, Node: Datasets, Next: Groups, Prev: Use of the NetCDF Library, Up: Top 2 Datasets ********** This chapter presents the interfaces of the netCDF functions that deal with a netCDF dataset or the whole netCDF library. A netCDF dataset that has not yet been opened can only be referred to by its dataset name. Once a netCDF dataset is opened, it is referred to by a netCDF ID, which is a small non-negative integer returned when you create or open the dataset. A netCDF ID is much like a file descriptor in C or a logical unit number in FORTRAN. In any single program, the netCDF IDs of distinct open netCDF datasets are distinct. A single netCDF dataset may be opened multiple times and will then have multiple distinct netCDF IDs; however at most one of the open instances of a single netCDF dataset should permit writing. When an open netCDF dataset is closed, the ID is no longer associated with a netCDF dataset. Functions that deal with the netCDF library include: * Get version of library. * Get error message corresponding to a returned error code. The operations supported on a netCDF dataset as a single object are: * Create, given dataset name and whether to overwrite or not. * Open for access, given dataset name and read or write intent. * Put into define mode, to add dimensions, variables, or attributes. * Take out of define mode, checking consistency of additions. * Close, writing to disk if required. * Inquire about the number of dimensions, number of variables, number of global attributes, and ID of the unlimited dimension, if any. * Synchronize to disk to make sure it is current. * Set and unset nofill mode for optimized sequential writes. * After a summary of conventions used in describing the netCDF interfaces, the rest of this chapter presents a detailed description of the interfaces for these operations. * Menu: * Interface Descriptions:: What's in the Function Documentation * parallel access:: * nc_strerror:: Get Error Messages * nc_inq_libvers:: Get netCDF library version * nc_create:: Create a Dataset * nc__create:: Create a Dataset with Performance Tuning * nc_create_par:: * nc_open:: Open a Dataset * nc__open:: Open a Dataset with Performance Tuning * nc_open_par:: * nc_redef:: Put a Dataset into Define Mode * nc_enddef:: Leave Define Mode * nc__enddef:: Leave Define Mode with Performance Tuning * nc_close:: Close a Dataset * nc_inq Family:: Inquire about a Dataset * nc_sync:: Synchronize a Dataset to Disk * nc_abort:: Back Out of Recent Definitions * nc_set_fill:: Set Fill Mode for Writes * nc_set_default_format:: Change the default output format * nc_set_chunk_cache:: * nc_get_chunk_cache::  File: netcdf-c.info, Node: Interface Descriptions, Next: parallel access, Prev: Datasets, Up: Datasets 2.1 NetCDF Library Interface Descriptions ========================================= Each interface description for a particular netCDF function in this and later chapters contains: * a description of the purpose of the function; * a C function prototype that presents the type and order of the formal parameters to the function; * a description of each formal parameter in the C interface; * a list of possible error conditions; and * an example of a C program fragment calling the netCDF function (and perhaps other netCDF functions). The examples follow a simple convention for error handling, always checking the error status returned from each netCDF function call and calling a handle_error function in case an error was detected. For an example of such a function, see *note nc_strerror::.  File: netcdf-c.info, Node: parallel access, Next: nc_strerror, Prev: Interface Descriptions, Up: Datasets 2.2 Parallel Access for NetCDF Files ==================================== To use parallel access, open or create the file with nc_open_par (see *note nc_open_par::) or nc_create_par (see *note nc_create_par::). The mode flag NC_PNETCDF will be automatically turned on for classic or 64-bit offset files opened or created with the parallel access functions. The following example shows the creation of a file using parallel access with a netCDF-4/HDF5 file, and how a program might write data to such a file. #include "netcdf.h" #include #include #include "hdf5.h" #include #include #define BAIL(e) do { \ printf("Bailing out in file %s, line %d, error:%s.\n", __FILE__, __LINE__, nc_strerror(e)); \ return e; \ } while (0) #define FILE "test_par.nc" #define NDIMS 2 #define DIMSIZE 24 #define QTR_DATA (DIMSIZE*DIMSIZE/4) #define NUM_PROC 4 int main(int argc, char **argv) { /* MPI stuff. */ int mpi_namelen; char mpi_name[MPI_MAX_PROCESSOR_NAME]; int mpi_size, mpi_rank; MPI_Comm comm = MPI_COMM_WORLD; MPI_Info info = MPI_INFO_NULL; /* Netcdf-4 stuff. */ int ncid, v1id, dimids[NDIMS]; size_t start[NDIMS], count[NDIMS]; int data[DIMSIZE*DIMSIZE], j, i, res; /* Initialize MPI. */ MPI_Init(&argc,&argv); MPI_Comm_size(MPI_COMM_WORLD, &mpi_size); MPI_Comm_rank(MPI_COMM_WORLD, &mpi_rank); MPI_Get_processor_name(mpi_name, &mpi_namelen); printf("mpi_name: %s size: %d rank: %d\n", mpi_name, mpi_size, mpi_rank); /* Create a parallel netcdf-4 file. */ if ((res = nc_create_par(FILE, NC_NETCDF4|NC_MPIIO, comm, info, &ncid))) BAIL(res); /* Create two dimensions. */ if ((res = nc_def_dim(ncid, "d1", DIMSIZE, dimids))) BAIL(res); if ((res = nc_def_dim(ncid, "d2", DIMSIZE, &dimids[1]))) BAIL(res); /* Create one var. */ if ((res = nc_def_var(ncid, "v1", NC_INT, NDIMS, dimids, &v1id))) BAIL(res); if ((res = nc_enddef(ncid))) BAIL(res); /* Set up slab for this process. */ start[0] = mpi_rank * DIMSIZE/mpi_size; start[1] = 0; count[0] = DIMSIZE/mpi_size; count[1] = DIMSIZE; printf("mpi_rank=%d start[0]=%d start[1]=%d count[0]=%d count[1]=%d\n", mpi_rank, start[0], start[1], count[0], count[1]); /* Create phony data. We're going to write a 24x24 array of ints, in 4 sets of 144. */ printf("mpi_rank*QTR_DATA=%d (mpi_rank+1)*QTR_DATA-1=%d\n", mpi_rank*QTR_DATA, (mpi_rank+1)*QTR_DATA); for (i=mpi_rank*QTR_DATA; i<(mpi_rank+1)*QTR_DATA; i++) data[i] = mpi_rank; /*if ((res = nc_var_par_access(ncid, v1id, NC_COLLECTIVE))) BAIL(res);*/ if ((res = nc_var_par_access(ncid, v1id, NC_INDEPENDENT))) BAIL(res); /* Write slabs of phony data. */ if ((res = nc_put_vara_int(ncid, v1id, start, count, &data[mpi_rank*QTR_DATA]))) BAIL(res); /* Close the netcdf file. */ if ((res = nc_close(ncid))) BAIL(res); /* Shut down MPI. */ MPI_Finalize(); return 0; }  File: netcdf-c.info, Node: nc_strerror, Next: nc_inq_libvers, Prev: parallel access, Up: Datasets 2.3 Get error message corresponding to error status: nc_strerror ================================================================ The function nc_strerror returns a static reference to an error message string corresponding to an integer netCDF error status or to a system error number, presumably returned by a previous call to some other netCDF function. The list of netCDF error status codes is available in the appropriate include file for each language binding. Usage ===== const char * nc_strerror(int ncerr); `ncerr' An error status that might have been returned from a previous call to some netCDF function. Errors ====== If you provide an invalid integer error status that does not correspond to any netCDF error message or or to any system error message (as understood by the system strerror function), nc_strerror returns a string indicating that there is no such error status. Example ======= Here is an example of a simple error handling function that uses nc_strerror to print the error message corresponding to the netCDF error status returned from any netCDF function call and then exit: #include ... void handle_error(int status) { if (status != NC_NOERR) { fprintf(stderr, "%s\n", nc_strerror(status)); exit(-1); } }  File: netcdf-c.info, Node: nc_inq_libvers, Next: nc_create, Prev: nc_strerror, Up: Datasets 2.4 Get netCDF library version: nc_inq_libvers ============================================== The function nc_inq_libvers returns a string identifying the version of the netCDF library, and when it was built. Usage ===== const char * nc_inq_libvers(void); Errors ====== This function takes no arguments, and thus no errors are possible in its invocation. Example ======= Here is an example using nc_inq_libvers to print the version of the netCDF library with which the program is linked: #include ... printf("%s\n", nc_inq_libvers());  File: netcdf-c.info, Node: nc_create, Next: nc__create, Prev: nc_inq_libvers, Up: Datasets 2.5 Create a NetCDF Dataset: nc_create ====================================== This function creates a new netCDF dataset, returning a netCDF ID that can subsequently be used to refer to the netCDF dataset in other netCDF function calls. The new netCDF dataset opened for write access and placed in define mode, ready for you to add dimensions, variables, and attributes. A creation mode flag specifies: * whether to overwrite any existing dataset with the same name, * whether access to the dataset is shared, * whether this file should be in netCDF classic format (the default), the new 64-bit offset format (use NC_64BIT_OFFSET), or NC_NETCDF4 for a netCDF-4/HDF5 file. Usage ===== NOTE: When creating a netCDF-4 file HDF5 error reporting is turned off, if it is on. This doesn't stop the HDF5 error stack from recording the errors, it simply stops their display to the user through stderr. int nc_create (const char* path, int cmode, int *ncidp); `path' The file name of the new netCDF dataset. `cmode' The creation mode flag. The following flags are available: NC_NOCLOBBER, NC_SHARE, NC_64BIT_OFFSET, NC_NETCDF4, NC_CLASSIC_MODEL. Setting NC_NOCLOBBER means you do not want to clobber (overwrite) an existing dataset; an error (NC_EEXIST) is returned if the specified dataset already exists. The NC_SHARE flag is appropriate when one process may be writing the dataset and one or more other processes reading the dataset concurrently; it means that dataset accesses are not buffered and caching is limited. Since the buffering scheme is optimized for sequential access, programs that do not access data sequentially may see some performance improvement by setting the NC_SHARE flag. This flag is ignored for netCDF-4 files. (See below.) Setting NC_64BIT_OFFSET causes netCDF to create a 64-bit offset format file, instead of a netCDF classic format file. The 64-bit offset format imposes far fewer restrictions on very large (i.e. over 2 GB) data files. *Note Large File Support: (netcdf)Large File Support. A zero value (defined for convenience as NC_CLOBBER) specifies the default behavior: overwrite any existing dataset with the same file name and buffer and cache accesses for efficiency. The dataset will be in netCDF classic format. *Note NetCDF Classic Format Limitations: (netcdf)NetCDF Classic Format Limitations. Setting NC_NETCDF4 causes netCDF to create a HDF5/NetCDF-4 file. Setting NC_CLASSIC_MODEL causes netCDF to enforce the classic data model in this file. (This only has effect for netCDF-4/HDF5 files, as classic and 64-bit offset files always use the classic model.) When used with NC_NETCDF4, this flag ensures that the resulting netCDF-4/HDF5 file may never contain any new constructs from the enhanced data model. That is, it cannot contain groups, user defined types, multiple unlimited dimensions, or new atomic types. The advantage of this restriction is that such files are guaranteed to work with existing netCDF software. `ncidp' Pointer to location where returned netCDF ID is to be stored. Errors ====== nc_create returns the value NC_NOERR if no errors occurred. Possible causes of errors include: * Passing a dataset name that includes a directory that does not exist. * Specifying a dataset name of a file that exists and also specifying NC_NOCLOBBER. * Specifying a meaningless value for the creation mode. * Attempting to create a netCDF dataset in a directory where you don't have permission to create files. Return Codes ============ `NC_NOERR' No error. `NC_ENOMEM' System out of memory. `NC_EHDFERR' HDF5 error (netCDF-4 files only). `NC_EFILEMETA' Error writing netCDF-4 file-level metadata in HDF5 file. (netCDF-4 files only). Examples ======== In this example we create a netCDF dataset named foo.nc; we want the dataset to be created in the current directory only if a dataset with that name does not already exist: #include ... int status; int ncid; ... status = nc_create("foo.nc", NC_NOCLOBBER, &ncid); if (status != NC_NOERR) handle_error(status); In this example we create a netCDF dataset named foo_large.nc. It will be in the 64-bit offset format. #include ... int status; int ncid; ... status = nc_create("foo_large.nc", NC_NOCLOBBER|NC_64BIT_OFFSET, &ncid); if (status != NC_NOERR) handle_error(status); In this example we create a netCDF dataset named foo_HDF5.nc. It will be in the HDF5 format. #include ... int status; int ncid; ... status = nc_create("foo_HDF5.nc", NC_NOCLOBBER|NC_NETCDF4, &ncid); if (status != NC_NOERR) handle_error(status); In this example we create a netCDF dataset named foo_HDF5_classic.nc. It will be in the HDF5 format, but will not allow the use of any netCDF-4 advanced features. That is, it will conform to the classic netCDF-3 data model. #include ... int status; int ncid; ... status = nc_create("foo_HDF5_classic.nc", NC_NOCLOBBER|NC_NETCDF4|NC_CLASSIC_MODEL, &ncid); if (status != NC_NOERR) handle_error(status); A variant of nc_create, nc__create (note the double underscore) allows users to specify two tuning parameters for the file that it is creating. These tuning parameters are not written to the data file, they are only used for so long as the file remains open after an nc__create. *Note nc__create::.  File: netcdf-c.info, Node: nc__create, Next: nc_create_par, Prev: nc_create, Up: Datasets 2.6 Create a NetCDF Dataset With Performance Options: nc__create ================================================================ This function is a variant of nc_create, nc__create (note the double underscore) allows users to specify two tuning parameters for the file that it is creating. These tuning parameters are not written to the data file, they are only used for so long as the file remains open after an nc__create. This function creates a new netCDF dataset, returning a netCDF ID that can subsequently be used to refer to the netCDF dataset in other netCDF function calls. The new netCDF dataset opened for write access and placed in define mode, ready for you to add dimensions, variables, and attributes. A creation mode flag specifies whether to overwrite any existing dataset with the same name and whether access to the dataset is shared, and whether this file should be in netCDF classic format (the default), or the new 64-bit offset format. Usage ===== int nc__create(const char *path, int cmode, size_t initialsz, size_t *bufrsizehintp, int *ncidp); `path' The file name of the new netCDF dataset. `cmode' The creation mode flag. The following flags are available: NC_NOCLOBBER, NC_SHARE, and NC_64BIT_OFFSET, NC_NETCDF4, NC_CLASSIC_MODEL. Setting NC_NOCLOBBER means you do not want to clobber (overwrite) an existing dataset; an error (NC_EEXIST) is returned if the specified dataset already exists. The NC_SHARE flag is appropriate when one process may be writing the dataset and one or more other processes reading the dataset concurrently; it means that dataset accesses are not buffered and caching is limited. Since the buffering scheme is optimized for sequential access, programs that do not access data sequentially may see some performance improvement by setting the NC_SHARE flag. This flag is ignored for netCDF-4 files. (See below.) Setting NC_64BIT_OFFSET causes netCDF to create a 64-bit offset format file, instead of a netCDF classic format file. The 64-bit offset format imposes far fewer restrictions on very large (i.e. over 2 GB) data files. *Note Large File Support: (netcdf)Large File Support. A zero value (defined for convenience as NC_CLOBBER) specifies the default behavior: overwrite any existing dataset with the same file name and buffer and cache accesses for efficiency. The dataset will be in netCDF classic format. *Note NetCDF Classic Format Limitations: (netcdf)NetCDF Classic Format Limitations. Setting NC_NETCDF4 causes netCDF to create a HDF5/NetCDF-4 file. Setting NC_CLASSIC_MODEL causes netCDF to enforce the classic data model in this file. (This only has effect for netCDF-4/HDF5 files, as classic and 64-bit offset files always use the classic model.) When used with NC_NETCDF4, this flag ensures that the resulting netCDF-4/HDF5 file may never contain any new constructs from the enhanced data model. That is, it cannot contain groups, user defined types, multiple unlimited dimensions, or new atomic types. The advantage of this restriction is that such files are guaranteed to work with existing netCDF software. `initialsz' On some systems, and with custom I/O layers, it may be advantageous to set the size of the output file at creation time. This parameter sets the initial size of the file at creation time. `bufrsizehintp' The argument referenced by bufrsizehintp controls a space versus time tradeoff, memory allocated in the netcdf library versus number of system calls. Because of internal requirements, the value may not be set to exactly the value requested. The actual value chosen is returned by reference. Using the value NC_SIZEHINT_DEFAULT causes the library to choose a default. How the system chooses the default depends on the system. On many systems, the "preferred I/O block size" is available from the stat() system call, struct stat member st_blksize. If this is available it is used. Lacking that, twice the system pagesize is used. Lacking a call to discover the system pagesize, we just set default bufrsize to 8192. The bufrsize is a property of a given open netcdf descriptor ncid, it is not a persistent property of the netcdf dataset. `ncidp' Pointer to location where returned netCDF ID is to be stored. Errors ====== nc_create returns the value NC_NOERR if no errors occurred. Possible causes of errors include: * Passing a dataset name that includes a directory that does not exist. * Specifying a dataset name of a file that exists and also specifying NC_NOCLOBBER. * Specifying a meaningless value for the creation mode. * Attempting to create a netCDF dataset in a directory where you don't have permission to create files. Return Codes ============ `NC_NOERR' No error. `NC_ENOMEM' System out of memory. `NC_EHDFERR' HDF5 error (netCDF-4 files only). `NC_EFILEMETA' Error writing netCDF-4 file-level metadata in HDF5 file. (netCDF-4 files only). Examples ======== In this example we create a netCDF dataset named foo.nc; we want the dataset to be created in the current directory only if a dataset with that name does not already exist: #include ... int status; int ncid; ... status = nc_create("foo.nc", NC_NOCLOBBER, &ncid); if (status != NC_NOERR) handle_error(status); In this example we create a netCDF dataset named foo_large.nc; we want the dataset to be created in the current directory only if a dataset with that name does not already exist. We also specify that bufrsize and initial size for the file. #include ... int status; int ncid; int intialsz = 2048; int *bufrsize; ... *bufrsize = 1024; status = nc__create("foo.nc", NC_NOCLOBBER, initialsz, bufrsize, &ncid); if (status != NC_NOERR) handle_error(status);  File: netcdf-c.info, Node: nc_create_par, Next: nc_open, Prev: nc__create, Up: Datasets 2.7 Create a NetCDF Dataset With Performance Options: nc_create_par =================================================================== This function is a variant of nc_create, nc_create_par allows users to open a file on a MPI/IO or MPI/Posix parallel file system. The parallel parameters are not written to the data file, they are only used for so long as the file remains open after an nc_create_par. This function creates a new netCDF dataset, returning a netCDF ID that can subsequently be used to refer to the netCDF dataset in other netCDF function calls. The new netCDF dataset opened for write access and placed in define mode, ready for you to add dimensions, variables, and attributes. If the NC_NETCDF4 flag is used, the HDF5 library is used for parallel I/O. If not, the parallel-netcdf library is used. When a file is created for parallel access, collective operations are the default. To use independent access on a variable, *Note nc_var_par_access::. Usage ===== int nc_create_par(const char *path, int cmode, MPI_Comm comm, MPI_Info info, int ncidp); `path' The file name of the new netCDF dataset. `cmode' Either the NC_MPIIO or NC_MPIPOSIX flags may be present if the NC_NETCDF4 flag is used. The NC_SHARE flag is ignored. `comm' The MPI_Comm object returned by the MPI layer. `info' The MPI_Info object returned by the MPI layer, if MPI/IO is being used, or 0 if MPI/Posix is being used. `ncidp' Pointer to location where returned netCDF ID is to be stored. Return Codes ============ `NC_NOERR' No error. `NC_EPARINIT' Could not initialize parallel access at the HDF5 layer. `NC_EFILEMETA' HDF5 layer cannot handle create or root group open. `NC_EEXIST' Specifying a dataset name of a file that exists and also specifying NC_NOCLOBBER. `NC_EINVAL' Bad value for the creation mode. `NC_EHDFERR' Unexpected error from the HDF5 layer. Examples ======== #include ... int status; int ncid; ... *bufrsize = 1024; status = nc__create("foo.nc", NC_NOCLOBBER, initialsz, bufrsize, &ncid); if (status != NC_NOERR) handle_error(status);  File: netcdf-c.info, Node: nc_open, Next: nc__open, Prev: nc_create_par, Up: Datasets 2.8 Open a NetCDF Dataset for Access: nc_open ============================================= The function nc_open opens an existing netCDF dataset for access. It determines the underlying file format automatically. Use the same call to open a netCDF classic, 64-bit offset, or netCDF-4 file. Usage ===== int nc_open (const char *path, int omode, int *ncidp); `path' File name for netCDF dataset to be opened. When DAP support is enabled, then the path may be an OPeNDAP URL rather than a file path. `omode' A zero value (or NC_NOWRITE) specifies the default behavior: open the dataset with read-only access, buffering and caching accesses for efficiency Otherwise, the open mode is NC_WRITE, NC_SHARE, or NC_WRITE|NC_SHARE. Setting the NC_WRITE flag opens the dataset with read-write access. ("Writing" means any kind of change to the dataset, including appending or changing data, adding or renaming dimensions, variables, and attributes, or deleting attributes.) The NC_SHARE flag is only used for netCDF classic and 64-bit offset files. It is appropriate when one process may be writing the dataset and one or more other processes reading the dataset concurrently; it means that dataset accesses are not buffered and caching is limited. Since the buffering scheme is optimized for sequential access, programs that do not access data sequentially may see some performance improvement by setting the NC_SHARE flag. It is not necessary to pass any information about the format of the file being opened. The file type will be detected automatically by the netCDF library. If a the path is a DAP URL, then the open mode is read-only. Setting NC_WRITE will be ignored. `ncidp' Pointer to location where returned netCDF ID is to be stored. Errors ====== When opening a netCDF-4 file HDF5 error reporting is turned off, if it is on. This doesn't stop the HDF5 error stack from recording the errors, it simply stops their display to the user through stderr. nc_open returns the value NC_NOERR if no errors occurred. Otherwise, the returned status indicates an error. Possible causes of errors include: * The specified netCDF dataset does not exist. * A meaningless mode was specified. Return Codes ============ `NC_NOERR' No error. `NC_NOMEM' Out of memory. `NC_EHDFERR' HDF5 error. (NetCDF-4 files only.) `NC_EDIMMETA' Error in netCDF-4 dimension metadata. (NetCDF-4 files only.) `NC_ENOCOMPOIND' (NetCDF-4 files only.) Example ======= Here is an example using nc_open to open an existing netCDF dataset named foo.nc for read-only, non-shared access: #include ... int status; int ncid; ... status = nc_open("foo.nc", 0, &ncid); if (status != NC_NOERR) handle_error(status);  File: netcdf-c.info, Node: nc__open, Next: nc_open_par, Prev: nc_open, Up: Datasets 2.9 Open a NetCDF Dataset for Access with Performance Tuning: nc__open ====================================================================== A function opens a netCDF dataset for access with an additional performance tuning parameter. When DAP support is enabled, it is possible to open a DAP data source through this interface, but it is deprecated because all of the performance tuning parameters are ignored. The standard nc_open interface should be used instead. Usage ===== int nc__open(const char *path, int mode, size_t *bufrsizehintp, int *ncidp); `path' File name for netCDF dataset to be opened. `omode' A zero value (or NC_NOWRITE) specifies the default behavior: open the dataset with read-only access, buffering and caching accesses for efficiency Otherwise, the open mode is NC_WRITE, NC_SHARE, or NC_WRITE|NC_SHARE. Setting the NC_WRITE flag opens the dataset with read-write access. ("Writing" means any kind of change to the dataset, including appending or changing data, adding or renaming dimensions, variables, and attributes, or deleting attributes.) The NC_SHARE flag is appropriate when one process may be writing the dataset and one or more other processes reading the dataset concurrently; it means that dataset accesses are not buffered and caching is limited. Since the buffering scheme is optimized for sequential access, programs that do not access data sequentially may see some performance improvement by setting the NC_SHARE flag. `bufrsizehintp' The argument referenced by bufrsizehintp controls a space versus time tradeoff, memory allocated in the netcdf library versus number of system calls. Because of internal requirements, the value may not be set to exactly the value requested. The actual value chosen is returned by reference. Using the value NC_SIZEHINT_DEFAULT causes the library to choose a default. How the system chooses the default depends on the system. On many systems, the "preferred I/O block size" is available from the stat() system call, struct stat member st_blksize. If this is available it is used. Lacking that, twice the system pagesize is used. Lacking a call to discover the system pagesize, we just set default bufrsize to 8192. The bufrsize is a property of a given open netcdf descriptor ncid, it is not a persistent property of the netcdf dataset. `ncidp' Pointer to location where returned netCDF ID is to be stored. Errors ====== nc__open returns the value NC_NOERR if no errors occurred. Otherwise, the returned status indicates an error. Possible causes of errors include: * The specified netCDF dataset does not exist. * A meaningless mode was specified. Example ======= Here is an example using nc__open to open an existing netCDF dataset named foo.nc for read-only, non-shared access: #include ... int status; int ncid; size_t bufrsize; ... *bufrsize = 1024; status = nc_open("foo.nc", 0, &bufrsize, &ncid); if (status != NC_NOERR) handle_error(status);  File: netcdf-c.info, Node: nc_open_par, Next: nc_redef, Prev: nc__open, Up: Datasets 2.10 Open a NetCDF Dataset for Parallel Access ============================================== This function opens a netCDF-4 dataset for parallel access. For netcdf-4/HDF5 files, the HDF5 library parallel I/O is used. This opens the file using either MPI-IO or MPI-POSIX. DAP access is not allowed with parallel I/O. When netCDF opens a file for parallel access, collective operations are the default. To use independent access on a variable, *Note nc_var_par_access::. Usage ===== int nc_open_par(const char *path, int mode, MPI_Comm comm, MPI_Info info, int *ncidp); `path' File name for netCDF dataset to be opened. `omode' Either the NC_MPIIO or NC_MPIPOSIX flags may be present for a netCDF-4/HDF5 file. The flag NC_WRITE opens the dataset with read-write access. ("Writing" means any kind of change to the dataset, including appending or changing data, adding or renaming dimensions, variables, and attributes, or deleting attributes.) All other flags are ignored or not allowed. The NC_NETCDF4 flag is not required, as the file type is detected when the file is opened. `comm' MPI_Comm object returned by the MPI layer. `info' MPI_Info object returned by the MPI layer, or NULL if MPI-POSIX access is desired. `ncidp' Pointer to location where returned netCDF ID is to be stored. Return Codes ============ `NC_NOERR' No error. `' The specified netCDF dataset does not exist. `' A meaningless mode was specified. Example ======= Here is an example (from nc_test4/tst_parallel2.c) using nc_open_par. /* Reopen the file and check it. */ if (nc_open_par(file_name, NC_NOWRITE, comm, info, &ncid)) ERR; /* Read all the slabs this process is responsible for. */ for (i = 0; i < NUM_SLABS / mpi_size; i++) { start[0] = NUM_SLABS / mpi_size * mpi_rank + i; /* Read one slab of data. */ if (nc_get_vara_int(ncid, varid, start, count, data_in)) ERR; }  File: netcdf-c.info, Node: nc_redef, Next: nc_enddef, Prev: nc_open_par, Up: Datasets 2.11 Put Open NetCDF Dataset into Define Mode: nc_redef ======================================================= The function nc_redef puts an open netCDF dataset into define mode, so dimensions, variables, and attributes can be added or renamed and attributes can be deleted. Usage ===== For netCDF-4 files (i.e. files created with NC_NETCDF4 in the cmode, *note nc_create::), it is not necessary to call nc_redef unless the file was also created with NC_STRICT_NC3. For straight-up netCDF-4 files, nc_redef is called automatically, as needed. For all netCDF-4 files, the root ncid must be used. This is the ncid returned by nc_open and nc_create, and points to the root of the hierarchy tree for netCDF-4 files. int nc_redef(int ncid); `ncid' netCDF ID, from a previous call to nc_open or nc_create. Errors ====== nc_redef returns the value NC_NOERR if no errors occurred. Otherwise, the returned status indicates an error. Possible causes of errors include: * The specified netCDF dataset is already in define mode. This error code will only be returned for classic and 64-bit offset format files. * The specified netCDF dataset was opened for read-only. * The specified netCDF ID does not refer to an open netCDF dataset. Errors ====== `NC_NOERR' No error. `NC_EBADID' Bad ncid. `NC_EBADGRPID' The ncid must refer to the root group of the file, that is, the group returned by nc_open or nc_create. (*note nc_open:: *note nc_create::). `NC_EINDEFINE' Already in define mode. `NC_EPERM' File is read-only. Example ======= Here is an example using nc_redef to open an existing netCDF dataset named foo.nc and put it into define mode: #include ... int status; int ncid; ... status = nc_open("foo.nc", NC_WRITE, &ncid); /* open dataset */ if (status != NC_NOERR) handle_error(status); ... status = nc_redef(ncid); /* put in define mode */ if (status != NC_NOERR) handle_error(status);  File: netcdf-c.info, Node: nc_enddef, Next: nc__enddef, Prev: nc_redef, Up: Datasets 2.12 Leave Define Mode: nc_enddef ================================= The function nc_enddef takes an open netCDF dataset out of define mode. The changes made to the netCDF dataset while it was in define mode are checked and committed to disk if no problems occurred. Non-record variables may be initialized to a "fill value" as well. *Note nc_set_fill::. The netCDF dataset is then placed in data mode, so variable data can be read or written. It's not necessary to call nc_enddef for netCDF-4 files. With netCDF-4 files, nc_enddef is called when needed by the netcdf-4 library. User calls to nc_enddef for netCDF-4 files still flush the metadata to disk. This call may involve copying data under some circumstances. For a more extensive discussion see *note File Structure and Performance: (netcdf)File Structure and Performance. For netCDF-4/HDF5 format files there are some variable settings (the compression, endianness, fletcher32 error correction, and fill value) which must be set (if they are going to be set at all) between the nc_def_var and the next nc_enddef. Once the nc_enddef is called, these settings can no longer be changed for a variable. Usage ===== int nc_enddef(int ncid); `ncid' NetCDF ID, from a previous call to nc_open or nc_create. If you use a group id, the enddef will apply to the entire file. That all, the enddef will not just end define mode in one group, but in the entire file. Errors ====== nc_enddef returns the value NC_NOERR if no errors occurred. Otherwise, the returned status indicates an error. Possible causes of errors include: * The specified netCDF dataset is not in define mode. * The specified netCDF ID does not refer to an open netCDF dataset. * The size of one or more variables exceed the size constraints for whichever variant of the file format is in use). *Note Large File Support: (netcdf)Large File Support. Example ======= Here is an example using nc_enddef to finish the definitions of a new netCDF dataset named foo.nc and put it into data mode: #include ... int status; int ncid; ... status = nc_create("foo.nc", NC_NOCLOBBER, &ncid); if (status != NC_NOERR) handle_error(status); ... /* create dimensions, variables, attributes */ status = nc_enddef(ncid); /*leave define mode*/ if (status != NC_NOERR) handle_error(status);  File: netcdf-c.info, Node: nc__enddef, Next: nc_close, Prev: nc_enddef, Up: Datasets 2.13 Leave Define Mode with Performance Tuning: nc__enddef ========================================================== The function nc__enddef takes an open netCDF dataset out of define mode. The changes made to the netCDF dataset while it was in define mode are checked and committed to disk if no problems occurred. Non-record variables may be initialized to a "fill value" as well. *Note nc_set_fill::. The netCDF dataset is then placed in data mode, so variable data can be read or written. This call may involve copying data under some circumstances. For a more extensive discussion see *note File Structure and Performance: (netcdf)File Structure and Performance. Caution: this function exposes internals of the netcdf version 1 file format. Users should use nc_enddef in most circumstances. This function may not be available on future netcdf implementations. The current netcdf file format has three sections, the "header" section, the data section for fixed size variables, and the data section for variables which have an unlimited dimension (record variables). The header begins at the beginning of the file. The index (offset) of the beginning of the other two sections is contained in the header. Typically, there is no space between the sections. This causes copying overhead to accrue if one wishes to change the size of the sections, as may happen when changing names of things, text attribute values, adding attributes or adding variables. Also, for buffered i/o, there may be advantages to aligning sections in certain ways. The minfree parameters allow one to control costs of future calls to nc_redef, nc_enddef by requesting that minfree bytes be available at the end of the section. The align parameters allow one to set the alignment of the beginning of the corresponding sections. The beginning of the section is rounded up to an index which is a multiple of the align parameter. The flag value ALIGN_CHUNK tells the library to use the bufrsize (see above) as the align parameter. It has nothing to do with the chunking (multidimensional tiling) features of netCDF-4. The file format requires mod 4 alignment, so the align parameters are silently rounded up to multiples of 4. The usual call, nc_enddef(ncid); is equivalent to nc__enddef(ncid, 0, 4, 0, 4); The file format does not contain a "record size" value, this is calculated from the sizes of the record variables. This unfortunate fact prevents us from providing minfree and alignment control of the "records" in a netcdf file. If you add a variable which has an unlimited dimension, the third section will always be copied with the new variable added. Usage ===== int nc__enddef(int ncid, size_t h_minfree, size_t v_align, size_t v_minfree, size_t r_align); `ncid' NetCDF ID, from a previous call to nc_open or nc_create. `h_minfree' Sets the pad at the end of the "header" section. `v_align' Controls the alignment of the beginning of the data section for fixed size variables. `v_minfree' Sets the pad at the end of the data section for fixed size variables. `r_align' Controls the alignment of the beginning of the data section for variables which have an unlimited dimension (record variables). Errors ====== nc__enddef returns the value NC_NOERR if no errors occurred. Otherwise, the returned status indicates an error. Possible causes of errors include: * The specified netCDF dataset is not in define mode. * The specified netCDF ID does not refer to an open netCDF dataset. * The size of one or more variables exceed the size constraints for whichever variant of the file format is in use). *Note Large File Support: (netcdf)Large File Support. Example ======= Here is an example using nc_enddef to finish the definitions of a new netCDF dataset named foo.nc and put it into data mode: #include ... int status; int ncid; ... status = nc_create("foo.nc", NC_NOCLOBBER, &ncid); if (status != NC_NOERR) handle_error(status); ... /* create dimensions, variables, attributes */ status = nc_enddef(ncid); /*leave define mode*/ if (status != NC_NOERR) handle_error(status);  File: netcdf-c.info, Node: nc_close, Next: nc_inq Family, Prev: nc__enddef, Up: Datasets 2.14 Close an Open NetCDF Dataset: nc_close =========================================== The function nc_close closes an open netCDF dataset. If the dataset in define mode, nc_enddef will be called before closing. (In this case, if nc_enddef returns an error, nc_abort will automatically be called to restore the dataset to the consistent state before define mode was last entered.) After an open netCDF dataset is closed, its netCDF ID may be reassigned to the next netCDF dataset that is opened or created. Usage ===== For netCDF-4 files, the ncid of the root group must be passed into nc_close. int nc_close(int ncid); `ncid' NetCDF ID, from a previous call to nc_open or nc_create. Errors ====== nc_close returns the value NC_NOERR if no errors occurred. Otherwise, the returned status indicates an error. Possible causes of errors include: * Define mode was entered and the automatic call made to nc_enddef failed. * The specified netCDF ID does not refer to an open netCDF dataset. `NC_NOERR' No error. `NC_EBADID' Invalid id passed. `NC_EBADGRPID' ncid did not contain the root group id of this file. (NetCDF-4 only). Example ======= Here is an example using nc_close to finish the definitions of a new netCDF dataset named foo.nc and release its netCDF ID: #include ... int status; int ncid; ... status = nc_create("foo.nc", NC_NOCLOBBER, &ncid); if (status != NC_NOERR) handle_error(status); ... /* create dimensions, variables, attributes */ status = nc_close(ncid); /* close netCDF dataset */ if (status != NC_NOERR) handle_error(status);  File: netcdf-c.info, Node: nc_inq Family, Next: nc_sync, Prev: nc_close, Up: Datasets 2.15 Inquire about an Open NetCDF Dataset: nc_inq Family ======================================================== Members of the nc_inq family of functions return information about an open netCDF dataset, given its netCDF ID. Dataset inquire functions may be called from either define mode or data mode. The first function, nc_inq, returns values for the number of dimensions, the number of variables, the number of global attributes, and the dimension ID of the dimension defined with unlimited length, if any. The other functions in the family each return just one of these items of information. For C, these functions include nc_inq, nc_inq_ndims, nc_inq_nvars, nc_inq_natts, and nc_inq_unlimdim. An additional function, nc_inq_format, returns the (rarely needed) format version. No I/O is performed when these functions are called, since the required information is available in memory for each open netCDF dataset. Usage ===== int nc_inq (int ncid, int *ndimsp, int *nvarsp, int *ngattsp, int *unlimdimidp); int nc_inq_ndims (int ncid, int *ndimsp); int nc_inq_nvars (int ncid, int *nvarsp); int nc_inq_natts (int ncid, int *ngattsp); int nc_inq_unlimdim (int ncid, int *unlimdimidp); int nc_inq_format (int ncid, int *formatp); `ncid' NetCDF ID, from a previous call to nc_open or nc_create. `ndimsp' Pointer to location for returned number of dimensions defined for this netCDF dataset. `nvarsp' Pointer to location for returned number of variables defined for this netCDF dataset. `ngattsp' Pointer to location for returned number of global attributes defined for this netCDF dataset. `unlimdimidp' Pointer to location for returned ID of the unlimited dimension, if there is one for this netCDF dataset. If no unlimited length dimension has been defined, -1 is returned. `formatp' Pointer to location for returned format version, one of NC_FORMAT_CLASSIC, NC_FORMAT_64BIT, NC_FORMAT_NETCDF4, NC_FORMAT_NETCDF4_CLASSIC. Errors ====== All members of the nc_inq family return the value NC_NOERR if no errors occurred. Otherwise, the returned status indicates an error. Possible causes of errors include: * The specified netCDF ID does not refer to an open netCDF dataset. Example ======= Here is an example using nc_inq to find out about a netCDF dataset named foo.nc: #include ... int status, ncid, ndims, nvars, ngatts, unlimdimid; ... status = nc_open("foo.nc", NC_NOWRITE, &ncid); if (status != NC_NOERR) handle_error(status); ... status = nc_inq(ncid, &ndims, &nvars, &ngatts, &unlimdimid); if (status != NC_NOERR) handle_error(status);  File: netcdf-c.info, Node: nc_sync, Next: nc_abort, Prev: nc_inq Family, Up: Datasets 2.16 Synchronize an Open NetCDF Dataset to Disk: nc_sync ======================================================== The function nc_sync offers a way to synchronize the disk copy of a netCDF dataset with in-memory buffers. There are two reasons you might want to synchronize after writes: * To minimize data loss in case of abnormal termination, or * To make data available to other processes for reading immediately after it is written. But note that a process that already had the dataset open for reading would not see the number of records increase when the writing process calls nc_sync; to accomplish this, the reading process must call nc_sync. This function is backward-compatible with previous versions of the netCDF library. The intent was to allow sharing of a netCDF dataset among multiple readers and one writer, by having the writer call nc_sync after writing and the readers call nc_sync before each read. For a writer, this flushes buffers to disk. For a reader, it makes sure that the next read will be from disk rather than from previously cached buffers, so that the reader will see changes made by the writing process (e.g., the number of records written) without having to close and reopen the dataset. If you are only accessing a small amount of data, it can be expensive in computer resources to always synchronize to disk after every write, since you are giving up the benefits of buffering. An easier way to accomplish sharing (and what is now recommended) is to have the writer and readers open the dataset with the NC_SHARE flag, and then it will not be necessary to call nc_sync at all. However, the nc_sync function still provides finer granularity than the NC_SHARE flag, if only a few netCDF accesses need to be synchronized among processes. It is important to note that changes to the ancillary data, such as attribute values, are not propagated automatically by use of the NC_SHARE flag. Use of the nc_sync function is still required for this purpose. Sharing datasets when the writer enters define mode to change the data schema requires extra care. In previous releases, after the writer left define mode, the readers were left looking at an old copy of the dataset, since the changes were made to a new copy. The only way readers could see the changes was by closing and reopening the dataset. Now the changes are made in place, but readers have no knowledge that their internal tables are now inconsistent with the new dataset schema. If netCDF datasets are shared across redefinition, some mechanism external to the netCDF library must be provided that prevents access by readers during redefinition and causes the readers to call nc_sync before any subsequent access. When calling nc_sync, the netCDF dataset must be in data mode. A netCDF dataset in define mode is synchronized to disk only when nc_enddef is called. A process that is reading a netCDF dataset that another process is writing may call nc_sync to get updated with the changes made to the data by the writing process (e.g., the number of records written), without having to close and reopen the dataset. Data is automatically synchronized to disk when a netCDF dataset is closed, or whenever you leave define mode. Usage ===== int nc_sync(int ncid); `ncid' NetCDF ID, from a previous call to nc_open or nc_create. Errors ====== nc_sync returns the value NC_NOERR if no errors occurred. Otherwise, the returned status indicates an error. Possible causes of errors include: * The netCDF dataset is in define mode. * The specified netCDF ID does not refer to an open netCDF dataset. Example ======= Here is an example using nc_sync to synchronize the disk writes of a netCDF dataset named foo.nc: #include ... int status; int ncid; ... status = nc_open("foo.nc", NC_WRITE, &ncid); /* open for writing */ if (status != NC_NOERR) handle_error(status); ... /* write data or change attributes */ status = nc_sync(ncid); /* synchronize to disk */ if (status != NC_NOERR) handle_error(status);  File: netcdf-c.info, Node: nc_abort, Next: nc_set_fill, Prev: nc_sync, Up: Datasets 2.17 Back Out of Recent Definitions: nc_abort ============================================= You no longer need to call this function, since it is called automatically by nc_close in case the dataset is in define mode and something goes wrong with committing the changes. The function nc_abort just closes the netCDF dataset, if not in define mode. If the dataset is being created and is still in define mode, the dataset is deleted. If define mode was entered by a call to nc_redef, the netCDF dataset is restored to its state before definition mode was entered and the dataset is closed. Usage ===== int nc_abort(int ncid); `ncid' NetCDF ID, from a previous call to nc_open or nc_create. Errors ====== nc_abort returns the value NC_NOERR if no errors occurred. Otherwise, the returned status indicates an error. Possible causes of errors include: * When called from define mode while creating a netCDF dataset, deletion of the dataset failed. * The specified netCDF ID does not refer to an open netCDF dataset. Example ======= Here is an example using nc_abort to back out of redefinitions of a dataset named foo.nc: #include ... int ncid, status, latid; ... status = nc_open("foo.nc", NC_WRITE, &ncid);/* open for writing */ if (status != NC_NOERR) handle_error(status); ... status = nc_redef(ncid); /* enter define mode */ if (status != NC_NOERR) handle_error(status); ... status = nc_def_dim(ncid, "lat", 18L, &latid); if (status != NC_NOERR) { handle_error(status); status = nc_abort(ncid); /* define failed, abort */ if (status != NC_NOERR) handle_error(status); }  File: netcdf-c.info, Node: nc_set_fill, Next: nc_set_default_format, Prev: nc_abort, Up: Datasets 2.18 Set Fill Mode for Writes: nc_set_fill ========================================== This function is intended for advanced usage, to optimize writes under some circumstances described below. The function nc_set_fill sets the fill mode for a netCDF dataset open for writing and returns the current fill mode in a return parameter. The fill mode can be specified as either NC_FILL or NC_NOFILL. The default behavior corresponding to NC_FILL is that data is pre-filled with fill values, that is fill values are written when you create non-record variables or when you write a value beyond data that has not yet been written. This makes it possible to detect attempts to read data before it was written. For more information on the use of fill values see *note Fill Values::. For information about how to define your own fill values see *note Attribute Conventions: (netcdf)Attribute Conventions. The behavior corresponding to NC_NOFILL overrides the default behavior of prefilling data with fill values. This can be used to enhance performance, because it avoids the duplicate writes that occur when the netCDF library writes fill values that are later overwritten with data. A value indicating which mode the netCDF dataset was already in is returned. You can use this value to temporarily change the fill mode of an open netCDF dataset and then restore it to the previous mode. After you turn on NC_NOFILL mode for an open netCDF dataset, you must be certain to write valid data in all the positions that will later be read. Note that nofill mode is only a transient property of a netCDF dataset open for writing: if you close and reopen the dataset, it will revert to the default behavior. You can also revert to the default behavior by calling nc_set_fill again to explicitly set the fill mode to NC_FILL. There are three situations where it is advantageous to set nofill mode: 1. Creating and initializing a netCDF dataset. In this case, you should set nofill mode before calling nc_enddef and then write completely all non-record variables and the initial records of all the record variables you want to initialize. 2. Extending an existing record-oriented netCDF dataset. Set nofill mode after opening the dataset for writing, then append the additional records to the dataset completely, leaving no intervening unwritten records. 3. Adding new variables that you are going to initialize to an existing netCDF dataset. Set nofill mode before calling nc_enddef then write all the new variables completely. If the netCDF dataset has an unlimited dimension and the last record was written while in nofill mode, then the dataset may be shorter than if nofill mode was not set, but this will be completely transparent if you access the data only through the netCDF interfaces. The use of this feature may not be available (or even needed) in future releases. Programmers are cautioned against heavy reliance upon this feature. Usage ===== int nc_set_fill (int ncid, int fillmode, int *old_modep); `ncid' NetCDF ID, from a previous call to nc_open or nc_create. `fillmode' Desired fill mode for the dataset, either NC_NOFILL or NC_FILL. `old_modep' Pointer to location for returned current fill mode of the dataset before this call, either NC_NOFILL or NC_FILL. Return Codes ============ `NC_NOERR' No error. `NC_EBADID' The specified netCDF ID does not refer to an open netCDF dataset. `NC_EPERM' The specified netCDF ID refers to a dataset open for read-only access. `NC_EINVAL' The fill mode argument is neither NC_NOFILL nor NC_FILL. Example ======= Here is an example using nc_set_fill to set nofill mode for subsequent writes of a netCDF dataset named foo.nc: #include ... int ncid, status, old_fill_mode; ... status = nc_open("foo.nc", NC_WRITE, &ncid); /* open for writing */ if (status != NC_NOERR) handle_error(status); ... /* write data with default prefilling behavior */ status = nc_set_fill(ncid, NC_NOFILL, &old_fill_mode); /* set nofill */ if (status != NC_NOERR) handle_error(status); ... /* write data with no prefilling */  File: netcdf-c.info, Node: nc_set_default_format, Next: nc_set_chunk_cache, Prev: nc_set_fill, Up: Datasets 2.19 Set Default Creation Format: nc_set_default_format ======================================================= This function is intended for advanced users. Starting in version 3.6, netCDF introduced a new data format, the first change in the underlying binary data format since the netCDF interface was released. The new format, 64-bit offset format, was introduced to greatly relax the limitations on creating very large files. Users are warned that creating files in the 64-bit offset format makes them unreadable by the netCDF library prior to version 3.6.0. For reasons of compatibility, users should continue to create files in netCDF classic format. Users who do want to use 64-bit offset format files can create them directory from nc_create, using the proper cmode flag. (*note nc_create::). The function nc_set_default_format allows the user to change the format of the netCDF file to be created by future calls to nc_create (or nc__create) without changing the cmode flag. This allows the user to convert a program to use 64-bit offset formation without changing all calls the nc_create. *Note Large File Support: (netcdf)Large File Support. Once the default format is set, all future created files will be in the desired format. Two constants are provided in the netcdf.h file to be used with this function, NC_FORMAT_64BIT and NC_FORMAT_CLASSIC. If a non-NULL pointer is provided, it is assumed to point to an int, where the existing default format will be written. Using nc_create with a cmode including NC_64BIT_OFFSET overrides the default format, and creates a 64-bit offset file. Usage ===== int nc_set_default_format(int format, int *old_formatp); `format' Valid formats include NC_FORMAT_CLASSIC (the default), NC_FORMAT_64BIT, and, if -enable-netcdf-4 was used during configure, NC_FORMAT_NETCDF4 and NC_FORMAT_NETCDF4_CLASSIC `old_formatp' Either NULL (in which case it will be ignored), or a pointer to an int where the existing default format (i.e. before being changed to the new format) will be written. This allows you to get the existing default format while setting a new default format. Return Codes ============ `NC_NOERR' No error. `NC_EINVAL' Invalid format. Valid formats include NC_FORMAT_CLASSIC, NC_FORMAT_64BIT, and, if -enable-netcdf-4 was used during configure, NC_FORMAT_NETCDF4 and NC_FORMAT_NETCDF4_CLASSIC. Trying to set the default format to something else will result in an invalid argument error. Example ======= Here is an example using nc_set_default_format to create the same file in four formats with the same nc_create call (from libsrc4/tst_utf8.c): #include ... int ncid, varid, dimids[NDIMS]; int f; for (f = NC_FORMAT_CLASSIC; f < NC_FORMAT_NETCDF4_CLASSIC; f++) { if (nc_set_default_format(f, NULL)) ERR; if (nc_create(FILE_NAME, NC_CLOBBER, &ncid)) ERR; ...  File: netcdf-c.info, Node: nc_set_chunk_cache, Next: nc_get_chunk_cache, Prev: nc_set_default_format, Up: Datasets 2.20 Set HDF5 Chunk Cache for Future File Opens/Creates: nc_set_chunk_cache =========================================================================== This function changes the default chunk cache settings in the HDF5 library for all variables in the file. The settings apply for subsequent file opens/creates. This function does not change the chunk cache settings of already open files. For more information, see the documentation for the H5Pset_cache() function in the HDF5 library at the HDF5 website: `http://hdfgroup.org/HDF5/'. Usage ===== int nc_set_chunk_cache(size_t size, size_t nelems, float preemption); `size' The total size of the raw data chunk cache, in bytes. This should be big enough to hold multiple chunks of data. `nelems' The number of chunk slots in the raw data chunk cache hash table. This should be a prime number larger than the number of chunks that will be in the cache. `preemption' The preemtion value must be between 0 and 1 inclusive and indicates how much chunks that have been fully read are favored for preemption. A value of zero means fully read chunks are treated no differently than other chunks (the preemption is strictly LRU) while a value of one means fully read chunks are always preempted before other chunks. Return Codes ============ `NC_NOERR' No error. `NC_EINVAL' Preemption must be between zero and one (inclusive). Example ======= This example is from libsrc4/tst_files.c: #include ... #define NEW_CACHE_SIZE 32000000 #define NEW_CACHE_NELEMS 2000 #define NEW_CACHE_PREEMPTION .75 /* Change chunk cache. */ if (nc_set_chunk_cache(NEW_CACHE_SIZE, NEW_CACHE_NELEMS, NEW_CACHE_PREEMPTION)) ERR; /* Create a file with two dims, two vars, and two atts. */ if (nc_create(FILE_NAME, cflags|NC_CLOBBER, &ncid)) ERR; ...  File: netcdf-c.info, Node: nc_get_chunk_cache, Prev: nc_set_chunk_cache, Up: Datasets 2.21 Get the HDF5 Chunk Cache Settings for Future File Opens/Creates: nc_get_chunk_cache ======================================================================================== This function gets the chunk cache settings for the HDF5 library. The settings apply for subsequent file opens/creates. This affects the per-file chunk cache which the HDF5 layer maintains. The chunk cache size can be tuned for better performance. For more information, see the documentation for the H5Pget_cache() function in the HDF5 library at the HDF5 website: `http://hdfgroup.org/HDF5/'. Usage ===== int nc_get_chunk_cache(size_t *sizep, size_t *nelemsp, float *preemptionp); `sizep' The total size of the raw data chunk cache will be put here. If NULL, will be ignored. `nelemsp' The number of chunk slots in the raw data chunk cache hash table will be put here. If NULL, will be ignored. `preemptionp' The preemption will be put here. The preemtion value is between 0 and 1 inclusive and indicates how much chunks that have been fully read are favored for preemption. A value of zero means fully read chunks are treated no differently than other chunks (the preemption is strictly LRU) while a value of one means fully read chunks are always preempted before other chunks. If NULL, will be ignored. Return Codes ============ `NC_NOERR' No error. Example ======= This example is from libsrc4/tst_files.c: #include ... /* Retrieve the chunk cache settings, just for fun. */ if (nc_get_chunk_cache(&cache_size_in, &cache_nelems_in, &cache_preemption_in)) ERR; if (cache_size_in != NEW_CACHE_SIZE || cache_nelems_in != NEW_CACHE_NELEMS || cache_preemption_in != NEW_CACHE_PREEMPTION) ERR; ...  File: netcdf-c.info, Node: Groups, Next: Dimensions, Prev: Datasets, Up: Top 3 Groups ******** NetCDF-4 added support for hierarchical groups within netCDF datasets. Groups are identified with a ncid, which identifies both the open file, and the group within that file. When a file is opened with nc_open or nc_create, the ncid for the root group of that file is provided. Using that as a starting point, users can add new groups, or list and navigate existing groups. All netCDF calls take a ncid which determines where the call will take its action. For example, the nc_def_var function takes a ncid as its first parameter. It will create a variable in whichever group its ncid refers to. Use the root ncid provided by nc_create or nc_open to create a variable in the root group. Or use nc_def_grp to create a group and use its ncid to define a variable in the new group. Variable are only visible in the group in which they are defined. The same applies to attributes. "Global" attributes are associated with the group whose ncid is used. Dimensions are visible in their groups, and all child groups. Group operations are only permitted on netCDF-4 files - that is, files created with the HDF5 flag in nc_create. (*note nc_create::). Groups are not compatible with the netCDF classic data model, so files created with the NC_CLASSIC_MODEL file cannot contain groups (except the root group). * Menu: * nc_inq_ncid:: * nc_inq_grps:: * nc_inq_varids:: * nc_inq_dimids:: * nc_inq_grpname:: * nc_inq_grpname_full:: * nc_inq_grpname_len:: * nc_inq_grp_parent:: * nc_inq_grp_ncid:: * nc_inq_grp_full_ncid:: * nc_def_grp::  File: netcdf-c.info, Node: nc_inq_ncid, Next: nc_inq_grps, Prev: Groups, Up: Groups 3.1 Find a Group ID: nc_inq_ncid ================================ Given an ncid and group name (NULL or "" gets root group), return ncid of the named group. Usage ===== int nc_inq_ncid(int ncid, const char *name, int *grp_ncid); `ncid' The group id for this operation. `name' A char array that holds the name of the desired group. `grp_ncid' An int pointer that will receive the group id, if the group is found. Errors ====== `NC_NOERR' No error. `NC_EBADID' Bad group id. `NC_ENOTNC4' Attempting a netCDF-4 operation on a netCDF-3 file. NetCDF-4 operations can only be performed on files defined with a create mode which includes flag HDF5. (*note nc_open::). `NC_ESTRICTNC3' This file was created with the strict netcdf-3 flag, therefore netcdf-4 operations are not allowed. (*note nc_open::). `NC_EHDFERR' An error was reported by the HDF5 layer. Example ======= int root_ncid, child_ncid; char file[] = "nc4_test.nc"; /* Open the file. */ if ((res = nc_open(file, NC_NOWRITE, &root_ncid))) return res; /* Get the ncid of an existing group. */ if ((res = nc_inq_ncid(root_ncid, "group1", &child_ncid))) return res;  File: netcdf-c.info, Node: nc_inq_grps, Next: nc_inq_varids, Prev: nc_inq_ncid, Up: Groups 3.2 Get a List of Groups in a Group: nc_inq_grps ================================================ Given a location id, return the number of groups it contains, and an array of their ncids. Usage ===== int nc_inq_grps(int ncid, int *numgrps, int *ncids); `ncid' The group id for this operation. `numgrps' Pointer to an int which will get number of groups in this group. If NULL, it's ignored. `ncids' Pointer to a already allocated array of ints which will receive the ids of all the groups in this group. If NULL, it's ignored. Call this function with NULL for ncids parameter to find out how many groups there are. Errors ====== `NC_NOERR' No error. `NC_EBADID' Bad group id. `NC_ENOTNC4' Attempting a netCDF-4 operation on a netCDF-3 file. NetCDF-4 operations can only be performed on files defined with a create mode which includes flag HDF5. (*note nc_open::). `NC_ESTRICTNC3' This file was created with the strict netcdf-3 flag, therefore netcdf-4 operations are not allowed. (*note nc_open::). `NC_EHDFERR' An error was reported by the HDF5 layer. Example ======= int root_ncid, numgrps; int *ncids; char file[] = "nc4_test.nc"; /* Open the file. */ if ((res = nc_open(file, NC_NOWRITE, &root_ncid))) return res; /* Get a list of ncids for the root group. (That is, find out of there are any groups already defined. */ if ((res = nc_inq_grps(root_ncid, &numgrps, NULL))) return res; ncids = malloc(sizeof(int) * numgrps); if ((res = nc_inq_grps(root_ncid, NULL, ncids))) return res;  File: netcdf-c.info, Node: nc_inq_varids, Next: nc_inq_dimids, Prev: nc_inq_grps, Up: Groups 3.3 Find all the Variables in a Group: nc_inq_varids ==================================================== Find all varids for a location. Usage ===== nc_inq_varids(int ncid, int *nvars, int *varids); `ncid' The group id for this operation. `nvars' The integer pointed to by this parameter will get the number of variable IDs found. `varids' An already allocated array to store the list of varids. Ignored if NULL. Errors ====== `NC_NOERR' No error. `NC_EBADID' Bad group id. `NC_ENOTNC4' Attempting a netCDF-4 operation on a netCDF-3 file. NetCDF-4 operations can only be performed on files defined with a create mode which includes flag HDF5. (*note nc_open::). `NC_ESTRICTNC3' This file was created with the strict netcdf-3 flag, therefore netcdf-4 operations are not allowed. (*note nc_open::). `NC_EHDFERR' An error was reported by the HDF5 layer. Example ======= This example is from libsrc4/tst_vars.c. int nvars_in, varids_in[2]; ... /* Open the file and make sure nc_inq_varids yeilds correct * result. */ if (nc_open(FILE_NAME, NC_NOWRITE, &ncid)) ERR; if (nc_inq_varids(ncid, &nvars_in, varids_in)) ERR;  File: netcdf-c.info, Node: nc_inq_dimids, Next: nc_inq_grpname, Prev: nc_inq_varids, Up: Groups 3.4 Find all Dimensions Visible in a Group: nc_inq_dimids ========================================================= Find all dimids for a location. This finds all dimensions in a group, or any of its parents. Usage ===== int nc_inq_dimids(int ncid, int *ndims, int *dimids, int include_parents); `ncid' The group id for this operation. `dimids' An already allocated array of ints when the dimids of the visible dimensions will be stashed. Use nc_inq_ndims to find out how many dims are visible from this group. (*note nc_inq Family::). `include_parents' If non-zero then all the dimensions in all parent groups will also be retrieved. Errors ====== `NC_NOERR' No error. `NC_EBADID' Bad group id. `NC_ENOTNC4' Attempting a netCDF-4 operation on a netCDF-3 file. NetCDF-4 operations can only be performed on files defined with a create mode which includes flag HDF5. (*note nc_open::). `NC_ESTRICTNC3' This file was created with the strict netcdf-3 flag, therefore netcdf-4 operations are not allowed. (*note nc_open::). `NC_EHDFERR' An error was reported by the HDF5 layer. Example ======= This example is from libsrc4/tst_dims.c. int ncid, dimid; int ndims_in, dimids_in[MAX_DIMS]; ... /* Open the file and make sure nc_inq_dimids yeilds correct * result. */ if (nc_open(FILE_NAME, NC_NOWRITE, &ncid)) ERR; if (nc_inq_dimids(ncid, &ndims_in, dimids_in, 0)) ERR; if (ndims_in != 1 || dimids_in[0] != 0) ERR;  File: netcdf-c.info, Node: nc_inq_grpname, Next: nc_inq_grpname_full, Prev: nc_inq_dimids, Up: Groups 3.5 Find a Group's Name: nc_inq_grpname ======================================= Given a group ID find its name. (Root group is named "/"). *Note nc_inq_grpname_full::. Usage ===== int nc_inq_grpname(int ncid, char *name); `ncid' The group id for this operation. `name' Pointer to allocated space of correct length. The name of the group will be copied there. The name will be less than NC_MAX_NAME, not including a terminating NULL byte. `' Errors ====== `NC_NOERR' No error. `NC_EBADID' Bad group id. `NC_ENOTNC4' Attempting a netCDF-4 operation on a netCDF-3 file. NetCDF-4 operations can only be performed on files defined with a create mode which includes flag HDF5. (*note nc_open::). `NC_ESTRICTNC3' This file was created with the strict netcdf-3 flag, therefore netcdf-4 operations are not allowed. (*note nc_open::). `NC_EHDFERR' An error was reported by the HDF5 layer. Example ======= This example is from libsrc4/tst_grps.c. int grpid_in[MAX_SIBLING_GROUPS]; char name_in[NC_MAX_NAME + 1]; ... if (nc_inq_grpname(grpid_in[0], name_in)) ERR;  File: netcdf-c.info, Node: nc_inq_grpname_full, Next: nc_inq_grpname_len, Prev: nc_inq_grpname, Up: Groups 3.6 Find a Group's Full Name: nc_inq_grpname_full ================================================= Given ncid, find complete name of group. (Root group is named "/", a full "path" for each group is provided in the name, with groups separated with a forward slash / as in Unix directory names. For example "/group1/subgrp1/subsubgrp1") Usage ===== int nc_inq_grpname_full(int ncid, size_t *lenp, char *full_name); `ncid' The group id for this operation. `lenp' Pointer to a size_t which will get the length. (Note that this does not include the NULL terminator byte.) `full_name' Pointer to allocated space of correct length. The name of the group will be copied there. To find the required length, call nc_inq_grpname_len call this function with NULL for the full_name parameter, or call (*note nc_inq_grpname_len::). `' Errors ====== `NC_NOERR' No error. `NC_EBADID' Bad group id. `NC_ENOTNC4' Attempting a netCDF-4 operation on a netCDF-3 file. NetCDF-4 operations can only be performed on files defined with a create mode which includes flag HDF5. (*note nc_open::). `NC_ESTRICTNC3' This file was created with the strict netcdf-3 flag, therefore netcdf-4 operations are not allowed. (*note nc_open::). `NC_EHDFERR' An error was reported by the HDF5 layer. Example ======= This example is from the test program libsrc4/tst_grps.c. int grpid_in[MAX_SIBLING_GROUPS]; char full_name_in[NC_MAX_NAME * 10]; size_t len; ... if (nc_inq_grpname_full(grpid_in[0], &len, full_name_in)) ERR;  File: netcdf-c.info, Node: nc_inq_grpname_len, Next: nc_inq_grp_parent, Prev: nc_inq_grpname_full, Up: Groups 3.7 Find the Length of a Group's Full Name: nc_inq_grpname_len ============================================================== Given ncid, find len of the full name, as returned by nc_inq_grpname_full *Note nc_inq_grpname_full::. (Root group is named "/", with length 1.) Usage ===== int nc_inq_grpname_len(int ncid, size_t *lenp); `ncid' The group id for this operation. `lenp' Pointer to an int where the length will be placed. Length does not include NULL terminator. Errors ====== `NC_NOERR' No error. `NC_EBADID' Bad group id. `NC_ENOTNC4' Attempting a netCDF-4 operation on a netCDF-3 file. NetCDF-4 operations can only be performed on files defined with a create mode which includes flag HDF5. (*note nc_open::). `NC_ESTRICTNC3' This file was created with the strict netcdf-3 flag, therefore netcdf-4 operations are not allowed. (*note nc_open::). `NC_EHDFERR' An error was reported by the HDF5 layer. Example ======= This example is from libsrc4/tst_grps.c. int ncid; size_t len; ... if (nc_inq_grpname_len(ncid, &len)) ERR;  File: netcdf-c.info, Node: nc_inq_grp_parent, Next: nc_inq_grp_ncid, Prev: nc_inq_grpname_len, Up: Groups 3.8 Find a Group's Parent: nc_inq_grp_parent ============================================ Given ncid, find the ncid of the parent group. When used with the root group, this function returns the NC_ENOGRP error (since the root group has no parent.) Usage ===== int nc_inq_grp_parent(int ncid, int *parent_ncid); `ncid' The group id. `parent_ncid' Pointer to an int. The ncid of the group will be copied there. `' Errors ====== `NC_NOERR' No error. `NC_EBADID' Bad group id. `NC_ENOGRP' No parent group found (i.e. this is the root group). `NC_ENOTNC4' Attempting a netCDF-4 operation on a netCDF-3 file. NetCDF-4 operations can only be performed on files defined with a create mode which includes flag HDF5. (*note nc_open::). `NC_ESTRICTNC3' This file was created with the strict netcdf-3 flag, therefore netcdf-4 operations are not allowed. (*note nc_open::). `NC_EHDFERR' An error was reported by the HDF5 layer. Example ======= if (nc_create(FILE_NAME, NC_NETCDF4, &ncid)) ERR; if (nc_def_grp(ncid, HENRY_VII, &henry_vii_id)) ERR; if (nc_inq_grp_parent(henry_vii_id, &parent_ncid)) ERR; if (parent_ncid != ncid) ERR; if (nc_close(ncid)) ERR;  File: netcdf-c.info, Node: nc_inq_grp_ncid, Next: nc_inq_grp_full_ncid, Prev: nc_inq_grp_parent, Up: Groups 3.9 Find a Group by Name: nc_inq_grp_ncid ========================================= Given a group name an an ncid, find the ncid of the group id. Usage ===== int nc_inq_grp_ncid(int ncid, const char *grp_name, int *grp_ncid); `ncid' The group id to look in. `grp_name' The name of the group that should be found. `grp_ncid' A pointer to int which will get the group id, if it is found. Return Codes ============ The following return codes may be returned by this function. `NC_NOERR' No error. `NC_EBADID' Bad group id. `NC_EINVAL' No name provided or name longer than NC_MAX_NAME. `NC_ENOGRP' Named group not found. `NC_ENOTNC4' Attempting a netCDF-4 operation on a netCDF-3 file. NetCDF-4 operations can only be performed on files defined with a create mode which includes flag HDF5. (*note nc_open::). `NC_ESTRICTNC3' This file was created with the strict netcdf-3 flag, therefore netcdf-4 operations are not allowed. (*note nc_open::). `NC_EHDFERR' An error was reported by the HDF5 layer. Example ======= This example is from test program libsrc4/tst_grps.c. /* Reopen and recheck. */ if (nc_open(FILE_NAME, NC_NOWRITE, &ncid)) ERR; if (nc_inq_grp_ncid(ncid, SCI_FI, &g1id)) ERR;  File: netcdf-c.info, Node: nc_inq_grp_full_ncid, Next: nc_def_grp, Prev: nc_inq_grp_ncid, Up: Groups 3.10 Find a Group by its Fully-qualified Name: nc_inq_grp_full_ncid =================================================================== Given a fully qualified group name an an ncid, find the ncid of the group id. Usage ===== int nc_inq_grp_full_ncid(int ncid, char *full_name, int *grp_ncid); `ncid' The group id to look in. `full_name' The fully-qualified group name. `grp_ncid' A pointer to int which will get the group id, if it is found. Return Codes ============ The following return codes may be returned by this function. `NC_NOERR' No error. `NC_EBADID' Bad group id. `NC_EINVAL' No name provided or name longer than NC_MAX_NAME. `NC_ENOGRP' Named group not found. `NC_ENOTNC4' Attempting a netCDF-4 operation on a netCDF-3 file. NetCDF-4 operations can only be performed on files defined with a create mode which includes flag HDF5. (*note nc_open::). `NC_ESTRICTNC3' This file was created with the strict netcdf-3 flag, therefore netcdf-4 operations are not allowed. (*note nc_open::). `NC_EHDFERR' An error was reported by the HDF5 layer. Example ======= This example is from test program libsrc4/tst_grps.c. /* Reopen and recheck. */ if (nc_open(FILE_NAME, NC_NOWRITE, &ncid)) ERR; if (nc_inq_grp_ncid(ncid, SCI_FI, &g1id)) ERR;  File: netcdf-c.info, Node: nc_def_grp, Prev: nc_inq_grp_full_ncid, Up: Groups 3.11 Create a New Group: nc_def_grp =================================== Create a group. Its location id is returned in the new_ncid pointer. Usage ===== int nc_def_grp(int parent_ncid, const char *name, int *new_ncid); `parent_ncid' The group id of the parent group. `name' The name of the new group. `new_ncid' A pointer to an int. The ncid of the new group will be placed there. Errors ====== `NC_NOERR' No error. `NC_EBADID' Bad group id. `NC_ENAMEINUSE' That name is in use. Group names must be unique within a group, and must not be the same as any variable or type in the group. `NC_EMAXNAME' Name exceed max length NC_MAX_NAME. `NC_EBADNAME' Name contains illegal characters. `NC_ENOTNC4' Attempting a netCDF-4 operation on a netCDF-3 file. NetCDF-4 operations can only be performed on files defined with a create mode which includes flag HDF5. (*note nc_open::). `NC_ESTRICTNC3' This file was created with the strict netcdf-3 flag, therefore netcdf-4 operations are not allowed. (*note nc_open::). `NC_EHDFERR' An error was reported by the HDF5 layer. `NC_EPERM' Attempt to write to a read-only file. `NC_ENOTINDEFINE' Not in define mode. Example ======= int root_ncid, a1_ncid; char grpname[] = "assimilation1"; /* Get the ncid of the root group. */ if ((res = nc_inq_ncid(root_ncid, NULL, &root_ncid))) return res; /* Create a group. */ if ((res = nc_def_grp(root_ncid, grpname, &a1_ncid))) return res;  File: netcdf-c.info, Node: Dimensions, Next: User Defined Data Types, Prev: Groups, Up: Top 4 Dimensions ************ * Menu: * Dimensions Introduction:: * nc_def_dim:: Create a Dimension * nc_inq_dimid:: Get a Dimension ID from Its Name * nc_inq_dim Family:: Inquire about a Dimension * nc_rename_dim:: Rename a Dimension * nc_inq_unlimdims::  File: netcdf-c.info, Node: Dimensions Introduction, Next: nc_def_dim, Prev: Dimensions, Up: Dimensions 4.1 Dimensions Introduction =========================== Dimensions for a netCDF dataset are defined when it is created, while the netCDF dataset is in define mode. Additional dimensions may be added later by reentering define mode. A netCDF dimension has a name and a length. In a netCDF classic or 64-bit offset file, at most one dimension can have the unlimited length, which means variables using this dimension can grow along this dimension. In a netCDF-4 file multiple unlimited dimensions are supported. There is a suggested limit (100) to the number of dimensions that can be defined in a single netCDF dataset. The limit is the value of the predefined macro NC_MAX_DIMS. The purpose of the limit is to make writing generic applications simpler. They need only provide an array of NC_MAX_DIMS dimensions to handle any netCDF dataset. The implementation of the netCDF library does not enforce this advisory maximum, so it is possible to use more dimensions, if necessary, but netCDF utilities that assume the advisory maximums may not be able to handle the resulting netCDF datasets. Ordinarily, the name and length of a dimension are fixed when the dimension is first defined. The name may be changed later, but the length of a dimension (other than the unlimited dimension) cannot be changed without copying all the data to a new netCDF dataset with a redefined dimension length. Dimension lengths in the C interface are type size_t rather than type int to make it possible to access all the data in a netCDF dataset on a platform that only supports a 16-bit int data type, for example MSDOS. If dimension lengths were type int instead, it would not be possible to access data from variables with a dimension length greater than a 16-bit int can accommodate. A netCDF dimension in an open netCDF dataset is referred to by a small integer called a dimension ID. In the C interface, dimension IDs are 0, 1, 2, ..., in the order in which the dimensions were defined. Operations supported on dimensions are: * Create a dimension, given its name and length. * Get a dimension ID from its name. * Get a dimension's name and length from its ID. * Rename a dimension.  File: netcdf-c.info, Node: nc_def_dim, Next: nc_inq_dimid, Prev: Dimensions Introduction, Up: Dimensions 4.2 Create a Dimension: nc_def_dim ================================== The function nc_def_dim adds a new dimension to an open netCDF dataset in define mode. It returns (as an argument) a dimension ID, given the netCDF ID, the dimension name, and the dimension length. At most one unlimited length dimension, called the record dimension, may be defined for each classic or 64-bit offset netCDF dataset. NetCDF-4 datasets may have multiple unlimited dimensions. Usage ===== int nc_def_dim (int ncid, const char *name, size_t len, int *dimidp); `ncid' NetCDF group ID, from a previous call to nc_open, nc_create, nc_def_grp, etc. `name' Dimension name. `len' Length of dimension; that is, number of values for this dimension as an index to variables that use it. This should be either a positive integer (of type size_t) or the predefined constant NC_UNLIMITED. `dimidp' Pointer to location for returned dimension ID. Errors ====== nc_def_dim returns the value NC_NOERR if no errors occurred. Otherwise, the returned status indicates an error. Possible causes of errors include: * The netCDF dataset is not in definition mode. * The specified dimension name is the name of another existing dimension. * The specified length is not greater than zero. * The specified length is unlimited, but there is already an unlimited length dimension defined for this netCDF dataset. * The specified netCDF ID does not refer to an open netCDF dataset. Example ======= Here is an example using nc_def_dim to create a dimension named lat of length 18 and a unlimited dimension named rec in a new netCDF dataset named foo.nc: #include ... int status, ncid, latid, recid; ... status = nc_create("foo.nc", NC_NOCLOBBER, &ncid); if (status != NC_NOERR) handle_error(status); ... status = nc_def_dim(ncid, "lat", 18L, &latid); if (status != NC_NOERR) handle_error(status); status = nc_def_dim(ncid, "rec", NC_UNLIMITED, &recid); if (status != NC_NOERR) handle_error(status);  File: netcdf-c.info, Node: nc_inq_dimid, Next: nc_inq_dim Family, Prev: nc_def_dim, Up: Dimensions 4.3 Get a Dimension ID from Its Name: nc_inq_dimid ================================================== The function nc_inq_dimid returns (as an argument) the ID of a netCDF dimension, given the name of the dimension. If ndims is the number of dimensions defined for a netCDF dataset, each dimension has an ID between 0 and ndims-1. Usage ===== When searching for a dimension, the specified group is searched, and then its parent group, and then its grandparent group, etc., up to the root group. int nc_inq_dimid (int ncid, const char *name, int *dimidp); `ncid' NetCDF ID, from a previous call to nc_open or nc_create. `name' Dimension name. `dimidp' Pointer to location for the returned dimension ID. Errors ====== nc_inq_dimid returns the value NC_NOERR if no errors occurred. Otherwise, the returned status indicates an error. Possible causes of errors include: The name that was specified is not the name of a dimension in the netCDF dataset. The specified netCDF ID does not refer to an open netCDF dataset. Example ======= Here is an example using nc_inq_dimid to determine the dimension ID of a dimension named lat, assumed to have been defined previously in an existing netCDF dataset named foo.nc: #include ... int status, ncid, latid; ... status = nc_open("foo.nc", NC_NOWRITE, &ncid); /* open for reading */ if (status != NC_NOERR) handle_error(status); ... status = nc_inq_dimid(ncid, "lat", &latid); if (status != NC_NOERR) handle_error(status);  File: netcdf-c.info, Node: nc_inq_dim Family, Next: nc_rename_dim, Prev: nc_inq_dimid, Up: Dimensions 4.4 Inquire about a Dimension: nc_inq_dim Family ================================================ This family of functions returns information about a netCDF dimension. Information about a dimension includes its name and its length. The length for the unlimited dimension, if any, is the number of records written so far. The functions in this family include nc_inq_dim, nc_inq_dimname, and nc_inq_dimlen. The function nc_inq_dim returns all the information about a dimension; the other functions each return just one item of information. Usage ===== int nc_inq_dim (int ncid, int dimid, char* name, size_t* lengthp); int nc_inq_dimname (int ncid, int dimid, char *name); int nc_inq_dimlen (int ncid, int dimid, size_t *lengthp); `ncid' NetCDF ID, from a previous call to nc_open or nc_create. `dimid' Dimension ID, from a previous call to nc_inq_dimid or nc_def_dim. `name' Returned dimension name. The caller must allocate space for the returned name. The maximum possible length, in characters, of a dimension name is given by the predefined constant NC_MAX_NAME. (This doesn't include the null terminator, so declare your array to be size NC_MAX_NAME+1). The returned character array will be null-terminated. `lengthp' Pointer to location for returned length of dimension. For the unlimited dimension, this is the number of records written so far. Errors ====== These functions return the value NC_NOERR if no errors occurred. Otherwise, the returned status indicates an error. Possible causes of errors include: * The dimension ID is invalid for the specified netCDF dataset. * The specified netCDF ID does not refer to an open netCDF dataset. Example ======= Here is an example using nc_inq_dim to determine the length of a dimension named lat, and the name and current maximum length of the unlimited dimension for an existing netCDF dataset named foo.nc: #include ... int status, ncid, latid, recid; size_t latlength, recs; char recname[NC_MAX_NAME+1]; ... status = nc_open("foo.nc", NC_NOWRITE, &ncid); /* open for reading */ if (status != NC_NOERR) handle_error(status); status = nc_inq_unlimdim(ncid, &recid); /* get ID of unlimited dimension */ if (status != NC_NOERR) handle_error(status); ... status = nc_inq_dimid(ncid, "lat", &latid); /* get ID for lat dimension */ if (status != NC_NOERR) handle_error(status); status = nc_inq_dimlen(ncid, latid, &latlength); /* get lat length */ if (status != NC_NOERR) handle_error(status); /* get unlimited dimension name and current length */ status = nc_inq_dim(ncid, recid, recname, &recs); if (status != NC_NOERR) handle_error(status);  File: netcdf-c.info, Node: nc_rename_dim, Next: nc_inq_unlimdims, Prev: nc_inq_dim Family, Up: Dimensions 4.5 Rename a Dimension: nc_rename_dim ===================================== The function nc_rename_dim renames an existing dimension in a netCDF dataset open for writing. You cannot rename a dimension to have the same name as another dimension. For netCDF classic and 64-bit offset files, if the new name is longer than the old name, the netCDF dataset must be in define mode. For netCDF-4 files the dataset is switched to define more for the rename, regardless of the name length. Usage ===== int nc_rename_dim(int ncid, int dimid, const char* name); `ncid' NetCDF ID, from a previous call to nc_open or nc_create. `dimid' Dimension ID, from a previous call to nc_inq_dimid or nc_def_dim. `name' New dimension name. Errors ====== nc_rename_dim returns the value NC_NOERR if no errors occurred. Otherwise, the returned status indicates an error. Possible causes of errors include: * The new name is the name of another dimension. * The dimension ID is invalid for the specified netCDF dataset. * The specified netCDF ID does not refer to an open netCDF dataset. * The new name is longer than the old name and the netCDF dataset is not in define mode. Example ======= Here is an example using nc_rename_dim to rename the dimension lat to latitude in an existing netCDF dataset named foo.nc: #include ... int status, ncid, latid; ... status = nc_open("foo.nc", NC_WRITE, &ncid); /* open for writing */ if (status != NC_NOERR) handle_error(status); ... status = nc_redef(ncid); /* put in define mode to rename dimension */ if (status != NC_NOERR) handle_error(status); status = nc_inq_dimid(ncid, "lat", &latid); if (status != NC_NOERR) handle_error(status); status = nc_rename_dim(ncid, latid, "latitude"); if (status != NC_NOERR) handle_error(status); status = nc_enddef(ncid); /* leave define mode */ if (status != NC_NOERR) handle_error(status);  File: netcdf-c.info, Node: nc_inq_unlimdims, Prev: nc_rename_dim, Up: Dimensions 4.6 Find All Unlimited Dimension IDs: nc_inq_unlimdims ====================================================== In netCDF-4 files, it's possible to have multiple unlimited dimensions. This function returns a list of the unlimited dimension ids visible in a group. Dimensions are visible in a group if they have been defined in that group, or any ancestor group. Usage ===== int nc_inq_unlimdims(int ncid, int *nunlimdimsp, int *unlimdimidsp); `ncid' NetCDF group ID, from a previous call to nc_open, nc_create, nc_def_grp, etc. `nunlimdimsp' A pointer to an int which will get the number of visible unlimited dimensions. Ignored if NULL. `unlimdimidsp' A pointer to an already allocated array of int which will get the ids of all visible unlimited dimensions. Ignored if NULL. To allocate the correct length for this array, call nc_inq_unlimdims with a NULL for this parameter and use the nunlimdimsp parameter to get the number of visible unlimited dimensions. Errors ====== `NC_NOERR' No error. `NC_EBADID' Bad group id. `NC_ENOTNC4' Attempting a netCDF-4 operation on a netCDF-3 file. NetCDF-4 operations can only be performed on files defined with a create mode which includes flag HDF5. (*note nc_open::). `NC_ESTRICTNC3' This file was created with the strict netcdf-3 flag, therefore netcdf-4 operations are not allowed. (*note nc_open::). `NC_EHDFERR' An error was reported by the HDF5 layer. Example ======= int root_ncid, num_unlimdims, unlimdims[NC_MAX_DIMS]; char file[] = "nc4_test.nc"; int res; /* Open the file. */ if ((res = nc_open(file, NC_NOWRITE, &root_ncid))) return res; /* Find out if there are any unlimited dimensions in the root group. */ if ((res = nc_inq_unlimdims(root_ncid, &num_unlimdims, unlimdims))) return res; printf("nc_inq_unlimdims reports %d unlimited dimensions\n", num_unlimdims);  File: netcdf-c.info, Node: User Defined Data Types, Next: Variables, Prev: Dimensions, Up: Top 5 User Defined Data Types ************************* * Menu: * User Defined Types:: * nc_inq_typeids:: * nc_inq_typeid:: * nc_inq_type:: * nc_inq_user_type:: * Compound Types:: * nc_def_compound:: * nc_insert_compound:: * nc_insert_array_compound:: * nc_inq_compound:: * nc_inq_compound_name:: * nc_inq_compound_size:: * nc_inq_compound_nfields:: * nc_inq_compound_field:: * nc_inq_compound_fieldname:: * nc_inq_compound_fieldindex:: * nc_inq_compound_fieldoffset:: * nc_inq_compound_fieldtype:: * nc_inq_compound_fieldndims:: * nc_inq_compound_fielddim_sizes:: * Variable Length Array:: * nc_def_vlen:: * nc_inq_vlen:: * nc_free_vlen:: * nc_free_vlens:: * Opaque Type:: * nc_def_opaque:: * nc_inq_opaque:: * Enum Type:: * nc_def_enum:: * nc_insert_enum:: * nc_inq_enum:: * nc_inq_enum_member:: * nc_inq_enum_ident::  File: netcdf-c.info, Node: User Defined Types, Next: nc_inq_typeids, Prev: User Defined Data Types, Up: User Defined Data Types 5.1 User Defined Types Introduction =================================== NetCDF-4 has added support for four different user defined data types. User defined type may only be used in files created with the NC_NETCDF4 and without NC_CLASSIC_MODEL. `compound type' Like a C struct, a compound type is a collection of types, including other user defined types, in one package. `variable length array type' The variable length array may be used to store ragged arrays. `opaque type' This type has only a size per element, and no other type information. `enum type' Like an enumeration in C, this type lets you assign text values to integer values, and store the integer values. Users may construct user defined type with the various nc_def_* functions described in this section. They may learn about user defined types by using the nc_inq_ functions defined in this section. Once types are constructed, define variables of the new type with nc_def_var (*note nc_def_var::). Write to them with nc_put_var1, nc_put_var, nc_put_vara, or nc_put_vars (*note Variables::). Read data of user-defined type with nc_get_var1, nc_get_var, nc_get_vara, or nc_get_vars (*note Variables::). Create attributes of the new type with nc_put_att (*note nc_put_att_ type::). Read attributes of the new type with nc_get_att (*note nc_get_att_ type::).  File: netcdf-c.info, Node: nc_inq_typeids, Next: nc_inq_typeid, Prev: User Defined Types, Up: User Defined Data Types 5.2 Learn the IDs of All Types in Group: nc_inq_typeids ======================================================= Learn the number of types defined in a group, and their IDs. Usage ===== int nc_inq_typeids(int ncid, int *ntypes, int *typeids); `ncid' The group id. `ntypes' A pointer to int which will get the number of types defined in the group. If NULL, ignored. `typeids' A pointer to an int array which will get the typeids. If NULL, ignored. Errors ====== `NC_NOERR' No error. `NC_BADID' Bad ncid. Example ======= The following example is from the test program libsrc4/tst_enums.c. if (nc_open(FILE_NAME, NC_NOWRITE, &ncid)) ERR; /* Get type info. */ if (nc_inq_typeids(ncid, &ntypes, typeids)) ERR; if (ntypes != 1 || !typeids[0]) ERR;  File: netcdf-c.info, Node: nc_inq_typeid, Next: nc_inq_type, Prev: nc_inq_typeids, Up: User Defined Data Types 5.3 Find a Typeid from Group and Name: nc_inq_typeid ==================================================== Given a group ID and a type name, find the ID of the type. If the type is not found in the group, then the parents are searched. If still not found, the entire file is searched. Usage ===== int nc_inq_typeid(int ncid, const char *name, nc_type *typeidp); `ncid' The group id. `name' The name of a type. `typeidp' A pointer to an int which will get the typeid. Errors ====== `NC_NOERR' No error. `NC_EBADID' Bad ncid. `NC_EBADTYPE' Can't find type. Example ======= The following example is from the test program libsrc4/tst_vars.c. It tests that the correct names are given for atomic types. /* Check inquire of atomic types */ if (nc_inq_type(ncid, NC_BYTE, name_in, &size_in)) ERR; if (strcmp(name_in, "byte") || size_in != sizeof(char)) ERR; if (nc_inq_type(ncid, NC_CHAR, name_in, &size_in)) ERR; if (strcmp(name_in, "char") || size_in != sizeof(char)) ERR; if (nc_inq_type(ncid, NC_SHORT, name_in, &size_in)) ERR; if (strcmp(name_in, "short") || size_in != sizeof(short)) ERR; if (nc_inq_type(ncid, NC_INT, name_in, &size_in)) ERR; if (strcmp(name_in, "int") || size_in != sizeof(int)) ERR; if (nc_inq_type(ncid, NC_FLOAT, name_in, &size_in)) ERR; if (strcmp(name_in, "float") || size_in != sizeof(float)) ERR; if (nc_inq_type(ncid, NC_DOUBLE, name_in, &size_in)) ERR; if (strcmp(name_in, "double") || size_in != sizeof(double)) ERR; if (nc_inq_type(ncid, NC_UBYTE, name_in, &size_in)) ERR; if (strcmp(name_in, "ubyte") || size_in != sizeof(unsigned char)) ERR; if (nc_inq_type(ncid, NC_USHORT, name_in, &size_in)) ERR; if (strcmp(name_in, "ushort") || size_in != sizeof(unsigned short)) ERR; if (nc_inq_type(ncid, NC_UINT, name_in, &size_in)) ERR; if (strcmp(name_in, "uint") || size_in != sizeof(unsigned int)) ERR; if (nc_inq_type(ncid, NC_INT64, name_in, &size_in)) ERR; if (strcmp(name_in, "int64") || size_in != sizeof(long long)) ERR; if (nc_inq_type(ncid, NC_UINT64, name_in, &size_in)) ERR; if (strcmp(name_in, "uint64") || size_in != sizeof(unsigned long long)) ERR; if (nc_inq_type(ncid, NC_STRING, name_in, &size_in)) ERR; if (strcmp(name_in, "string") || size_in != 0) ERR; if (xtype_in != NC_SHORT) ERR;  File: netcdf-c.info, Node: nc_inq_type, Next: nc_inq_user_type, Prev: nc_inq_typeid, Up: User Defined Data Types 5.4 Learn About a User Defined Type: nc_inq_type ================================================ Given an ncid and a typeid, get the information about a type. This function will work on any type, including atomic and any user defined type, whether compound, opaque, enumeration, or variable length array. For even more information about a user defined type *note nc_inq_user_type::. Usage ===== nc_inq_type(int ncid, nc_type xtype, char *name, size_t *sizep); `ncid' The ncid for the group containing the type (ignored for atomic types). `xtype' The typeid for this type, as returned by nc_def_compound, nc_def_opaque, nc_def_enum, nc_def_vlen, or nc_inq_var, or as found in netcdf.h in the list of atomic types (NC_CHAR, NC_INT, etc.). `name' If non-NULL, the name of the user defined type will be copied here. It will be NC_MAX_NAME bytes or less. For atomic types, the type name from CDL will be given. `sizep' If non-NULL, the (in-memory) size of the type in bytes will be copied here. VLEN type size is the size of nc_vlen_t. String size is returned as the size of a character pointer. The size may be used to malloc space for the data, no matter what the type. Return Codes ============ `NC_NOERR' No error. `NC_EBADTYPEID' Bad typeid. `NC_ENOTNC4' Seeking a user-defined type in a netCDF-3 file. `NC_ESTRICTNC3' Seeking a user-defined type in a netCDF-4 file for which classic model has been turned on. `NC_EBADGRPID' Bad group ID in ncid. `NC_EBADID' Type ID not found. `NC_EHDFERR' An error was reported by the HDF5 layer. Example ======= This example is from the test program tst_enums.c, and it uses all the possible inquiry functions on an enum type. /* Check it out. */ if (nc_inq_user_type(ncid, typeids[0], name_in, &base_size_in, &base_nc_type_in, &nfields_in, &class_in)) ERR; if (strcmp(name_in, TYPE_NAME) || base_size_in != sizeof(int) || base_nc_type_in != NC_INT || nfields_in != NUM_MEMBERS || class_in != NC_ENUM) ERR; if (nc_inq_type(ncid, typeids[0], name_in, &base_size_in)) ERR; if (strcmp(name_in, TYPE_NAME) || base_size_in != sizeof(int)) ERR; if (nc_inq_enum(ncid, typeids[0], name_in, &base_nc_type, &base_size_in, &num_members)) ERR; if (strcmp(name_in, TYPE_NAME) || base_nc_type != NC_INT || num_members != NUM_MEMBERS) ERR; for (i = 0; i < NUM_MEMBERS; i++) { if (nc_inq_enum_member(ncid, typeid, i, name_in, &value_in)) ERR; if (strcmp(name_in, member_name[i]) || value_in != member_value[i]) ERR; if (nc_inq_enum_ident(ncid, typeid, member_value[i], name_in)) ERR; if (strcmp(name_in, member_name[i])) ERR; } if (nc_close(ncid)) ERR;  File: netcdf-c.info, Node: nc_inq_user_type, Next: Compound Types, Prev: nc_inq_type, Up: User Defined Data Types 5.5 Learn About a User Defined Type: nc_inq_user_type ===================================================== Given an ncid and a typeid, get the information about a user defined type. This function will work on any user defined type, whether compound, opaque, enumeration, or variable length array. Usage ===== nc_inq_user_type(int ncid, nc_type xtype, char *name, size_t *sizep, nc_type *base_nc_typep, size_t *nfieldsp, int *classp); `ncid' The ncid for the group containing the user defined type. `xtype' The typeid for this type, as returned by nc_def_compound, nc_def_opaque, nc_def_enum, nc_def_vlen, or nc_inq_var. `name' If non-NULL, the name of the user defined type will be copied here. It will be NC_MAX_NAME bytes or less. `sizep' If non-NULL, the (in-memory) size of the type in bytes will be copied here. VLEN type size is the size of nc_vlen_t. String size is returned as the size of a character pointer. The size may be used to malloc space for the data, no matter what the type. `nfieldsp' If non-NULL, the number of fields will be copied here for enum and compound types. `classp' Return the class of the user defined type, NC_VLEN, NC_OPAQUE, NC_ENUM, or NC_COMPOUND. Errors ====== `NC_NOERR' No error. `NC_EBADTYPEID' Bad typeid. `NC_EBADFIELDID' Bad fieldid. `NC_EHDFERR' An error was reported by the HDF5 layer. Example ======= /* Create a file. */ if (nc_create(FILE_NAME, NC_NETCDF4, &ncid)) ERR; /* Create an enum type. */ if (nc_def_enum(ncid, NC_INT, TYPE_NAME, &typeid)) ERR; for (i = 0; i < NUM_MEMBERS; i++) if (nc_insert_enum(ncid, typeid, member_name[i], &member_value[i])) ERR; /* Check it out. */ if (nc_inq_user_type(ncid, typeid, name_in, &base_size_in, &base_nc_type_in, &nfields_in, &class_in)) ERR; if (strcmp(name_in, TYPE_NAME) || base_size_in != sizeof(int) || base_nc_type_in != NC_INT || nfields_in != NUM_MEMBERS || class_in != NC_ENUM) ERR;  File: netcdf-c.info, Node: Compound Types, Next: nc_def_compound, Prev: nc_inq_user_type, Up: User Defined Data Types 5.6 Compound Types Introduction =============================== Compound data types can be defined for netCDF-4/HDF5 format files. A compound datatype is similar to a struct in C and contains a collection of one or more atomic or user-defined types. The netCDF-4 compound data must comply with the properties and constraints of the HDF5 compound data type in terms of which it is implemented. In summary these are: * It has a fixed total size. * It consists of zero or more named members that do not overlap with other members. * Each member has a name distinct from other members. * Each member has its own datatype. * Each member is referenced by an index number between zero and N-1, where N is the number of members in the compound datatype. * Each member has a fixed byte offset, which is the first byte (smallest byte address) of that member in the compound datatype. * In addition to other other user-defined data types or atomic datatypes, a member can be a small fixed-size array of any type with up to four fixed-size "dimensions" (not associated with named netCDF dimensions). Currently there is an HDF5 restriction on total size of a compound type to not larger than 2^16 = 65536 bytes. Attempts to exceed this limit result in an NC_EHDFERR error. Compound types are not supported in classic or 64-bit offset format files. To write data in a compound type, first use nc_def_compound to create the type, multiple calls to nc_insert_compound to add to the compound type, and then write data with the appropriate nc_put_var1, nc_put_vara, nc_put_vars, or nc_put_varm call. To read data written in a compound type, you must know its structure. Use the nc_inq_compound functions to learn about the compound type. * Menu: * nc_def_compound:: * nc_insert_compound:: * nc_inq_compound:: * nc_inq_compound_fieldname:: * nc_inq_compound_fieldindex:: * nc_inq_compound_fieldoffset:: * nc_inq_compound_fieldtype::  File: netcdf-c.info, Node: nc_def_compound, Next: nc_insert_compound, Prev: Compound Types, Up: User Defined Data Types 5.7 Creating a Compound Type: nc_def_compound ============================================= Create a compound type. Provide an ncid, a name, and a total size (in bytes) of one element of the completed compound type. After calling this function, fill out the type with repeated calls to nc_insert_compound (*note nc_insert_compound::). Call nc_insert_compound once for each field you wish to insert into the compound type. Note that there does not seem to be a way to read such types into structures in Fortran 90 (and there are no structures in Fortran 77). Usage ===== int nc_def_compound(int ncid, size_t size, const char *name, nc_type *typeidp); `ncid' The groupid where this compound type will be created. `size' The size, in bytes, of the compound type. `name' The name of the new compound type. `typeidp' A pointer to an nc_type. The typeid of the new type will be placed there. Errors ====== `NC_NOERR' No error. `NC_EBADID' Bad group id. `NC_ENAMEINUSE' That name is in use. `NC_EMAXNAME' Name exceeds max length NC_MAX_NAME. `NC_EBADNAME' Name contains illegal characters. `NC_ENOTNC4' Attempting a netCDF-4 operation on a netCDF-3 file. NetCDF-4 operations can only be performed on files defined with a create mode which includes flag NC_NETCDF4. (*note nc_open::). `NC_ESTRICTNC3' This file was created with the strict netcdf-3 flag, therefore netcdf-4 operations are not allowed. (*note nc_open::). `NC_EHDFERR' An error was reported by the HDF5 layer. `NC_EPERM' Attempt to write to a read-only file. `NC_ENOTINDEFINE' Not in define mode. Example ======= struct s1 { int i1; int i2; }; struct s1 data[DIM_LEN], data_in[DIM_LEN]; /* Create a file with a compound type. Write a little data. */ if (nc_create(FILE_NAME, NC_NETCDF4, &ncid)) ERR; if (nc_def_compound(ncid, sizeof(struct s1), SVC_REC, &typeid)) ERR; if (nc_insert_compound(ncid, typeid, BATTLES_WITH_KLINGONS, HOFFSET(struct s1, i1), NC_INT)) ERR; if (nc_insert_compound(ncid, typeid, DATES_WITH_ALIENS, HOFFSET(struct s1, i2), NC_INT)) ERR; if (nc_def_dim(ncid, STARDATE, DIM_LEN, &dimid)) ERR; if (nc_def_var(ncid, SERVICE_RECORD, typeid, 1, dimids, &varid)) ERR; if (nc_put_var(ncid, varid, data)) ERR; if (nc_close(ncid)) ERR;  File: netcdf-c.info, Node: nc_insert_compound, Next: nc_insert_array_compound, Prev: nc_def_compound, Up: User Defined Data Types 5.8 Inserting a Field into a Compound Type: nc_insert_compound ============================================================== Insert a named field into a compound type. Usage ===== int nc_insert_compound(int ncid, nc_type typeid, const char *name, size_t offset, nc_type field_typeid); `ncid' The groupid where a field for this compound type will be inserted. `typeid' The typeid for this compound type, as returned by nc_def_compound, or nc_inq_var. `name' The name of the new field. `offset' Offset in byte from the beginning of the compound type for this field. `field_typeid' The type of the field to be inserted. Errors ====== `NC_NOERR' No error. `NC_EBADID' Bad group id. `NC_ENAMEINUSE' That name is in use. Field names must be unique within a compound type. `NC_EMAXNAME' Name exceed max length NC_MAX_NAME. `NC_EBADNAME' Name contains illegal characters. `NC_ENOTNC4' Attempting a netCDF-4 operation on a netCDF-3 file. NetCDF-4 operations can only be performed on files defined with a create mode which includes flag NC_NETCDF4. (*note nc_open::). `NC_ESTRICTNC3' This file was created with the strict netcdf-3 flag, therefore netcdf-4 operations are not allowed. (*note nc_open::). `NC_EHDFERR' An error was reported by the HDF5 layer. `NC_ENOTINDEFINE' Not in define mode. Example =======  File: netcdf-c.info, Node: nc_insert_array_compound, Next: nc_inq_compound, Prev: nc_insert_compound, Up: User Defined Data Types 5.9 Inserting an Array Field into a Compound Type: nc_insert_array_compound =========================================================================== Insert a named field into a compound type. Usage ===== int nc_insert_array_compound(int ncid, nc_type xtype, const char *name, size_t offset, nc_type field_typeid, int ndims, const int *dim_sizes); `ncid' The ID of the file that contains the array type and the compound type. `xtype' The typeid for this compound type, as returned by nc_def_compound, or nc_inq_var. `name' The name of the new field. `offset' Offset in byte from the beginning of the compound type for this field. `field_typeid' The base type of the array to be inserted. Errors ====== `NC_NOERR' No error. `NC_EBADID' Bad group id. `NC_ENAMEINUSE' That name is in use. Field names must be unique within a compound type. `NC_EMAXNAME' Name exceed max length NC_MAX_NAME. `NC_EBADNAME' Name contains illegal characters. `NC_ENOTNC4' Attempting a netCDF-4 operation on a netCDF-3 file. NetCDF-4 operations can only be performed on files defined with a create mode which includes flag NC_NETCDF4. (*note nc_open::). `NC_ESTRICTNC3' This file was created with the strict netcdf-3 flag, therefore netcdf-4 operations are not allowed. (*note nc_open::). `NC_EHDFERR' An error was reported by the HDF5 layer. `NC_ENOTINDEFINE' Not in define mode. `NC_ETYPEDEFINED' Attempt to change type that has already been committed. The first time the file leaves define mode, all defined types are committed, and can't be changed. If you wish to add an array to a compound type, you must do so before the compound type is committed. Example ======= This example comes from the test file libsrc4/tst_compounds.c, which writes data about some Star Fleet officers who are known to use netCDF data. /* Since some aliens exists in different, or more than one, * dimensions, StarFleet keeps track of the dimensional abilities * of everyone on 7 dimensions. */ #define NUM_DIMENSIONS 7 struct dim_rec { int starfleet_id; int abilities[NUM_DIMENSIONS]; }; struct dim_rec dim_data_out[DIM_LEN], dim_data_in[DIM_LEN]; /* Create some phoney data. */ for (i=0; i ... int status; /* error status */ int ncid; /* netCDF ID */ int lat_dim, lon_dim, time_dim; /* dimension IDs */ int rh_id; /* variable ID */ int rh_dimids[3]; /* variable shape */ ... status = nc_create("foo.nc", NC_NOCLOBBER, &ncid); if (status != NC_NOERR) handle_error(status); ... /* define dimensions */ status = nc_def_dim(ncid, "lat", 5L, &lat_dim); if (status != NC_NOERR) handle_error(status); status = nc_def_dim(ncid, "lon", 10L, &lon_dim); if (status != NC_NOERR) handle_error(status); status = nc_def_dim(ncid, "time", NC_UNLIMITED, &time_dim); if (status != NC_NOERR) handle_error(status); ... /* define variable */ rh_dimids[0] = time_dim; rh_dimids[1] = lat_dim; rh_dimids[2] = lon_dim; status = nc_def_var (ncid, "rh", NC_DOUBLE, 3, rh_dimids, &rh_id); if (status != NC_NOERR) handle_error(status);  File: netcdf-c.info, Node: nc_def_var_chunking, Next: nc_inq_var_chunking, Prev: nc_def_var, Up: Variables 6.6 Define Chunking Parameters for a Variable: `nc_def_var_chunking' ==================================================================== The function nc_def_var_chunking sets the chunking parameters for a variable in a netCDF-4 file. It can set the chunk sizes to get chunked storage, or it can set the contiguous flag to get contiguous storage. Variables that make use of one or more unlimited dimensions, compression, or checksums must use chunking. Such variables are created with default chunk sizes of 1 for each unlimited dimension and the dimension length for other dimensions, except that if the resulting chunks are too large, the default chunk sizes for non-record dimensions are reduced. The total size of a chunk must be less than 4 GiB. That is, the product of all chunksizes and the size of the data (or the size of nc_vlen_t for VLEN types) must be less than 4 GiB. This function may only be called after the variable is defined, but before nc_enddef is called. Once the chunking parameters are set for a variable, they cannot be changed. This function can be used to change the default chunking for record, compressed, or checksummed variables before nc_enddef is called. Note that you cannot set chunking for scalar variables. Only non-scalar variables can have chunking. Usage ===== int nc_def_var_chunking(int ncid, int varid, int storage, size_t *chunksizesp); `ncid' NetCDF ID, from a previous call to nc_open or nc_create. `varid' Variable ID. `storage' If NC_CONTIGUOUS, then contiguous storage is used for this variable. Variables with chunking, compression, checksums, or one or more unlimited dimensions cannot use contiguous storage. If NC_CHUNKED, then chunked storage is used for this variable. Chunk sizes may be specified with the chunksizes parameter or default sizes will be used if that parameter is NULL. By default contiguous storage is used for fix-sized variables when conpression, chunking, and checksums are not used. `*chunksizes' A pointer to an array list of chunk sizes. The array must have one chunksize for each dimension of the variable. Errors ====== nc_def_var_chunking returns the value NC_NOERR if no errors occurred. Otherwise, the returned status indicates an error. Possible return codes include: `NC_NOERR' No error. `NC_EBADID' Bad ncid. `NC_EINVAL' Invalid input. This can occur if contiguous storage is set on a variable which uses compression, checksums, or one or more unlimited dimensions. `NC_ENOTNC4' Not a netCDF-4 file. `NC_ENOTVAR' Can't find this variable. `NC_ELATEDEF' This variable has already been the subject of a nc_enddef call. In netCDF-4 files nc_enddef will be called automatically for any data read or write. Once nc_enddef has been called after the nc_def_var call for a variable, it is impossible to set the chunking for that variable. `NC_ENOTINDEFINE' Not in define mode. This is returned for netCDF classic or 64-bit offset files, or for netCDF-4 files, when they were been created with NC_STRICT_NC3 flag. (*note nc_create::). `NC_ESTRICTNC3' Trying to create a var some place other than the root group in a netCDF file with NC_STRICT_NC3 turned on. `NC_EPERM' Attempt to create object in read-only file. Example ======= In this example from libsrc4/tst_vars2.c, chunksizes are set with nc_var_def_chunking, and checked with nc_var_inq_chunking. printf("**** testing chunking..."); { #define NDIMS5 1 #define DIM5_NAME "D5" #define VAR_NAME5 "V5" #define DIM5_LEN 1000 int dimids[NDIMS5], dimids_in[NDIMS5]; int varid; int ndims, nvars, natts, unlimdimid; nc_type xtype_in; char name_in[NC_MAX_NAME + 1]; int data[DIM5_LEN], data_in[DIM5_LEN]; size_t chunksize[NDIMS5] = {5}; size_t chunksize_in[NDIMS5]; int storage_in; int i, d; for (i = 0; i < DIM5_LEN; i++) data[i] = i; /* Create a netcdf-4 file with one dim and one var. */ if (nc_create(FILE_NAME, NC_NETCDF4, &ncid)) ERR; if (nc_def_dim(ncid, DIM5_NAME, DIM5_LEN, &dimids[0])) ERR; if (nc_def_var(ncid, VAR_NAME5, NC_INT, NDIMS5, dimids, &varid)) ERR; if (nc_def_var_chunking(ncid, varid, NC_CHUNKED, chunksize)) ERR; if (nc_put_var_int(ncid, varid, data)) ERR; /* Check stuff. */ if (nc_inq_var_chunking(ncid, varid, &storage_in, chunksize_in)) ERR; for (d = 0; d < NDIMS5; d++) if (chunksize[d] != chunksize_in[d]) ERR; if (storage_in != NC_CHUNKED) ERR;  File: netcdf-c.info, Node: nc_inq_var_chunking, Next: nc_set_var_chunk_cache, Prev: nc_def_var_chunking, Up: Variables 6.7 Learn About Chunking Parameters for a Variable: `nc_inq_var_chunking' ========================================================================= The function nc_inq_var_chunking returns the chunking settings for a variable in a netCDF-4 file. Usage ===== int nc_inq_var_chunking(int ncid, int varid, int *storagep, size_t *chunksizesp); `ncid' NetCDF ID, from a previous call to nc_open or nc_create. `varid' Variable ID. `storagep' Address of returned storage property, returned as NC_CONTIGUOUS if this variable uses contiguous storage, or NC_CHUNKEDif it uses chunked storage. `*chunksizesp' A pointer to an array list of chunk sizes. The array must have one chunksize for each dimension in the variable. Errors ====== nc_inq_var_chunking returns the value NC_NOERR if no errors occurred. Otherwise, the returned status indicates an error. Possible return codes include: `NC_NOERR' No error. `NC_BADID' Bad ncid. `NC_ENOTNC4' Not a netCDF-4 file. `NC_ENOTVAR' Can't find this variable. Example ======= This example is from libsrc4/tst_vars2.c in which a variable with contiguous storage is created, and then checked with nc_inq_var_chunking: printf("**** testing contiguous storage..."); { #define NDIMS6 1 #define DIM6_NAME "D5" #define VAR_NAME6 "V5" #define DIM6_LEN 100 int dimids[NDIMS6], dimids_in[NDIMS6]; int varid; int ndims, nvars, natts, unlimdimid; nc_type xtype_in; char name_in[NC_MAX_NAME + 1]; int data[DIM6_LEN], data_in[DIM6_LEN]; size_t chunksize_in[NDIMS6]; int storage_in; int i, d; for (i = 0; i < DIM6_LEN; i++) data[i] = i; /* Create a netcdf-4 file with one dim and one var. */ if (nc_create(FILE_NAME, NC_NETCDF4, &ncid)) ERR; if (nc_def_dim(ncid, DIM6_NAME, DIM6_LEN, &dimids[0])) ERR; if (dimids[0] != 0) ERR; if (nc_def_var(ncid, VAR_NAME6, NC_INT, NDIMS6, dimids, &varid)) ERR; if (nc_def_var_chunking(ncid, varid, NC_CONTIGUOUS, NULL)) ERR; if (nc_put_var_int(ncid, varid, data)) ERR; /* Check stuff. */ if (nc_inq_var_chunking(ncid, 0, &storage_in, chunksize_in)) ERR; if (storage_in != NC_CONTIGUOUS) ERR;  File: netcdf-c.info, Node: nc_set_var_chunk_cache, Next: nc_get_var_chunk_cache, Prev: nc_inq_var_chunking, Up: Variables 6.8 Set HDF5 Chunk Cache for a Variable: nc_set_var_chunk_cache =============================================================== This function changes the chunk cache settings for a variable. The change in cache size happens immediately. This is a property of the open file - it does not persist the next time you open the file. For more information, see the documentation for the H5Pset_cache() function in the HDF5 library at the HDF5 website: `http://hdfgroup.org/HDF5/'. Usage ===== nc_set_var_chunk_cache(int ncid, int varid, size_t size, size_t nelems, float preemption); `ncid' NetCDF ID, from a previous call to nc_open or nc_create. `varid' Variable ID. `size' The total size of the raw data chunk cache, in bytes. This should be big enough to hold multiple chunks of data. `nelems' The number of chunk slots in the raw data chunk cache hash table. This should be a prime number larger than the number of chunks that will be in the cache. `preemption' The preemtion value must be between 0 and 1 inclusive and indicates how much chunks that have been fully read are favored for preemption. A value of zero means fully read chunks are treated no differently than other chunks (the preemption is strictly LRU) while a value of one means fully read chunks are always preempted before other chunks. Return Codes ============ `NC_NOERR' No error. `NC_EINVAL' Preemption must be between zero and one (inclusive). Example ======= This example is from libsrc4/tst_vars2.c: #include ... #define CACHE_SIZE 32000000 #define CACHE_NELEMS 1009 #define CACHE_PREEMPTION .75 ... /* Create a netcdf-4 file with one dim and one var. */ if (nc_create(FILE_NAME, NC_NETCDF4, &ncid)) ERR; if (nc_def_dim(ncid, DIM5_NAME, DIM5_LEN, &dimids[0])) ERR; if (dimids[0] != 0) ERR; if (nc_def_var(ncid, VAR_NAME5, NC_INT, NDIMS5, dimids, &varid)) ERR; if (nc_def_var_chunking(ncid, varid, NC_CHUNKED, chunksize)) ERR; if (nc_set_var_chunk_cache(ncid, varid, CACHE_SIZE, CACHE_NELEMS, CACHE_PREEMPTION)) ERR;  File: netcdf-c.info, Node: nc_get_var_chunk_cache, Next: nc_def_var_fill, Prev: nc_set_var_chunk_cache, Up: Variables 6.9 Get the HDF5 Chunk Cache Settings for a Variable: nc_get_var_chunk_cache ============================================================================ This function gets the current chunk cache settings for a variable in a netCDF-4/HDF5 file. For more information, see the documentation for the H5Pget_cache() function in the HDF5 library at the HDF5 website: `http://hdfgroup.org/HDF5/'. Usage ===== int nc_get_var_chunk_cache(int ncid, int varid, size_t *sizep, size_t *nelemsp, float *preemptionp); `ncid' NetCDF ID, from a previous call to nc_open or nc_create. `varid' Variable ID. `sizep' The total size of the raw data chunk cache, in bytes, will be put here. If NULL, will be ignored. `nelemsp' The number of chunk slots in the raw data chunk cache hash table will be put here. If NULL, will be ignored. `preemptionp' The preemption will be put here. The preemtion value is between 0 and 1 inclusive and indicates how much chunks that have been fully read are favored for preemption. A value of zero means fully read chunks are treated no differently than other chunks (the preemption is strictly LRU) while a value of one means fully read chunks are always preempted before other chunks. If NULL, will be ignored. Return Codes ============ `NC_NOERR' No error. Example ======= This example is from libsrc4/tst_vars2.c: #include ... /* Create a netcdf-4 file with one dim and one var. */ if (nc_create(FILE_NAME, NC_NETCDF4, &ncid)) ERR; if (nc_def_dim(ncid, DIM5_NAME, DIM5_LEN, &dimids[0])) ERR; if (nc_def_var(ncid, VAR_NAME5, NC_INT, NDIMS5, dimids, &varid)) ERR; if (nc_def_var_chunking(ncid, varid, NC_CHUNKED, chunksize)) ERR; if (nc_set_var_chunk_cache(ncid, varid, CACHE_SIZE, CACHE_NELEMS, CACHE_PREEMPTION)) ERR; ... if (nc_get_var_chunk_cache(ncid, varid, &cache_size_in, &cache_nelems_in, &cache_preemption_in)) ERR; if (cache_size_in != CACHE_SIZE || cache_nelems_in != CACHE_NELEMS || cache_preemption_in != CACHE_PREEMPTION) ERR; ...  File: netcdf-c.info, Node: nc_def_var_fill, Next: nc_inq_var_fill, Prev: nc_get_var_chunk_cache, Up: Variables 6.10 Define Fill Parameters for a Variable: `nc_def_var_fill' ============================================================= The function nc_def_var_fill sets the fill parameters for a variable in a netCDF-4 file. This function must be called after the variable is defined, but before nc_enddef is called. Usage ===== int nc_def_var_fill(int ncid, int varid, int no_fill, void *fill_value); `ncid' NetCDF ID, from a previous call to nc_open or nc_create. `varid' Variable ID. `no_fill' Set no_fill mode on a variable. When this mode is on, fill values will not be written for the variable. This is helpful in high performance applications. For netCDF-4/HDF5 files (whether classic model or not), this may only be changed after the variable is defined, but before it is committed to disk (i.e. before the first nc_enddef after the nc_def_var.) For classic and 64-bit offset file, the no_fill mode may be turned on and off at any time. `*fill_value' A pointer to a value which will be used as the fill value for the variable. Must be the same type as the variable. This will be written to a _FillValue attribute, created for this purpose. If NULL, this argument will be ignored. Return Codes ============ `NC_NOERR' No error. `NC_BADID' Bad ncid. `NC_ENOTNC4' Not a netCDF-4 file. `NC_ENOTVAR' Can't find this variable. `NC_ELATEDEF' This variable has already been the subject of a nc_enddef call. In netCDF-4 files nc_enddef will be called automatically for any data read or write. Once enddef has been called, it is impossible to set the fill for a variable. `NC_ENOTINDEFINE' Not in define mode. This is returned for netCDF classic or 64-bit offset files, or for netCDF-4 files, when they were been created with NC_STRICT_NC3 flag. (*note nc_create::). `NC_EPERM' Attempt to create object in read-only file. Example ======= This example is from libsrc4/tst_vars.c int dimids[NDIMS]; size_t index[NDIMS]; int varid; int no_fill; unsigned short ushort_data = 42, ushort_data_in, fill_value_in; /* Create a netcdf-4 file with one dim and 1 NC_USHORT var. */ if (nc_create(FILE_NAME, NC_NETCDF4, &ncid)) ERR; if (nc_def_dim(ncid, DIM7_NAME, DIM7_LEN, &dimids[0])) ERR; if (nc_def_var(ncid, VAR7_NAME, NC_USHORT, NDIMS, dimids, &varid)) ERR; if (nc_def_var_fill(ncid, varid, 1, NULL)) ERR;  File: netcdf-c.info, Node: nc_inq_var_fill, Next: nc_def_var_deflate, Prev: nc_def_var_fill, Up: Variables 6.11 Learn About Fill Parameters for a Variable: `nc_inq_var_fill' ================================================================== The function nc_inq_var_fill returns the fill settings for a variable in a netCDF-4 file. Usage ===== int nc_inq_var_fill(int ncid, int varid, int *no_fill, void *fill_value); `ncid' NetCDF ID, from a previous call to nc_open or nc_create. `varid' Variable ID. `*no_fill' Pointer to an integer which will get a 1 if no_fill mode is set for this variable. *Note nc_def_var_fill::. This parameter will be ignored if it is NULL. `*fill_value' A pointer which will get the fill value for this variable. This parameter will be ignored if it is NULL. Return Codes ============ `NC_NOERR' No error. `NC_BADID' Bad ncid. `NC_ENOTNC4' Not a netCDF-4 file. `NC_ENOTVAR' Can't find this variable. Example ======= This example is from libsrc4/tst_vars.c int dimids[NDIMS]; size_t index[NDIMS]; int varid; int no_fill; unsigned short ushort_data = 42, ushort_data_in, fill_value_in; /* Create a netcdf-4 file with one dim and 1 NC_USHORT var. */ if (nc_create(FILE_NAME, NC_NETCDF4, &ncid)) ERR; if (nc_def_dim(ncid, DIM7_NAME, DIM7_LEN, &dimids[0])) ERR; if (nc_def_var(ncid, VAR7_NAME, NC_USHORT, NDIMS, dimids, &varid)) ERR; if (nc_def_var_fill(ncid, varid, 1, NULL)) ERR; /* Check stuff. */ if (nc_inq_var_fill(ncid, varid, &no_fill, &fill_value_in)) ERR; if (!no_fill) ERR;  File: netcdf-c.info, Node: nc_def_var_deflate, Next: nc_inq_var_deflate, Prev: nc_inq_var_fill, Up: Variables 6.12 Define Compression Parameters for a Variable: `nc_def_var_deflate' ======================================================================= The function nc_def_var_deflate sets the deflate parameters for a variable in a netCDF-4 file. This function must be called after the variable is defined, but before nc_enddef is called. This does not work with scalar variables. Usage ===== nc_def_var_deflate(int ncid, int varid, int shuffle, int deflate, int deflate_level); `ncid' NetCDF ID, from a previous call to nc_open or nc_create. `varid' Variable ID. `shuffle' If non-zero, turn on the shuffle filter. `deflate' If non-zero, turn on the deflate filter at the level specified by the deflate_level parameter. `deflate_level' If the deflate parameter is non-zero, set the deflate level to this value. Must be between 0 and 9. Errors ====== nc_def_var_deflate returns the value NC_NOERR if no errors occurred. Otherwise, the returned status indicates an error. Possible return codes include: `NC_NOERR' No error. `NC_BADID' Bad ncid. `NC_ENOTNC4' Not a netCDF-4 file. `NC_ENOTVAR' Can't find this variable. `NC_ELATEDEF' This variable has already been the subject of a nc_enddef call. In netCDF-4 files nc_enddef will be called automatically for any data read or write. Once enddef has been called, it is impossible to set the deflate for a variable. `NC_ENOTINDEFINE' Not in define mode. This is returned for netCDF classic or 64-bit offset files, or for netCDF-4 files, when they were been created with NC_STRICT_NC3 flag. (*note nc_create::). `NC_EPERM' Attempt to create object in read-only file. `NC_EINVAL' Invalid deflate_level. The deflate level must be between 0 and 9, inclusive. Example =======  File: netcdf-c.info, Node: nc_inq_var_deflate, Next: nc_inq_var_szip, Prev: nc_def_var_deflate, Up: Variables 6.13 Learn About Deflate Parameters for a Variable: `nc_inq_var_deflate' ======================================================================== The function nc_inq_var_deflate returns the deflate settings for a variable in a netCDF-4 file. Usage ===== nc_inq_var_deflate(int ncid, int varid, int *shufflep, int *deflatep, int *deflate_levelp); `ncid' NetCDF ID, from a previous call to nc_open or nc_create. `varid' Variable ID. `*shufflep' If this pointer is non-NULL, the nc_inq_var_deflate function will write a 1 if the shuffle filter is turned on for this variable, and a 0 otherwise. `*deflatep' If this pointer is non-NULL, the nc_inq_var_deflate function will write a 1 if the deflate filter is turned on for this variable, and a 0 otherwise. `*deflate_levelp' If this pointer is non-NULL, and the deflate filter is in use for this variable, the nc_inq_var_deflate function will write the deflate_level here. Errors ====== nc_inq_var_deflate returns the value NC_NOERR if no errors occurred. Otherwise, the returned status indicates an error. Possible return codes include: `NC_NOERR' No error. `NC_BADID' Bad ncid. `NC_ENOTNC4' Not a netCDF-4 file. `NC_ENOTVAR' Can't find this variable. Example =======  File: netcdf-c.info, Node: nc_inq_var_szip, Next: nc_def_var_fletcher32, Prev: nc_inq_var_deflate, Up: Variables 6.14 Learn About Szip Parameters for a Variable: `nc_inq_var_szip' ================================================================== The function nc_inq_var_szip returns the szip settings for a variable in a netCDF-4 file. Usage ===== int nc_inq_var_szip(int ncid, int varid, int *options_maskp, int *pixels_per_blockp); `ncid' NetCDF ID, from a previous call to nc_open or nc_create. `varid' Variable ID. `*options_maskp' If this pointer is non-NULL, the nc_inq_var_szip function will put the options_mask here. `*pixels_per_blockp' If this pointer is non-NULL, the nc_inq_var_szip function will write the bits per pixel here. Errors ====== nc_inq_var_szip returns the value NC_NOERR if no errors occurred. Otherwise, the returned status indicates an error. Possible return codes include: `NC_NOERR' No error. `NC_BADID' Bad ncid. `NC_ENOTNC4' Not a netCDF-4 file. `NC_ENOTVAR' Can't find this variable. Example ======= This example is from libsrc4/tst_vars3.c. /* Make sure we have the szip settings we expect. */ if (nc_inq_var_szip(ncid, small_varid, &options_mask_in, &pixels_per_block_in)) ERR; if (options_mask_in != 0 || pixels_per_block_in !=0) ERR; if (nc_inq_var_szip(ncid, medium_varid, &options_mask_in, &pixels_per_block_in)) ERR; if (!(options_mask_in & NC_SZIP_EC_OPTION_MASK) || pixels_per_block_in != 32) ERR; if (nc_inq_var_szip(ncid, large_varid, &options_mask_in, &pixels_per_block_in)) ERR; if (!(options_mask_in & NC_SZIP_NN_OPTION_MASK) || pixels_per_block_in != 16) ERR;  File: netcdf-c.info, Node: nc_def_var_fletcher32, Next: nc_inq_var_fletcher32, Prev: nc_inq_var_szip, Up: Variables 6.15 Define Checksum Parameters for a Variable: `nc_def_var_fletcher32' ======================================================================= The function nc_def_var_fletcher32 sets the checksum parameters for a variable in a netCDF-4 file. This function may only be called after the variable is defined, but before nc_enddef is called. Usage ===== nc_def_var_fletcher32(int ncid, int varid, int checksum); `ncid' NetCDF ID, from a previous call to nc_open or nc_create. `varid' Variable ID. `checksum' If this is NC_FLETCHER32, fletcher32 checksums will be turned on for this variable. Errors ====== nc_def_var_fletcher32 returns the value NC_NOERR if no errors occurred. Otherwise, the returned status indicates an error. Possible return codes include: `NC_NOERR' No error. `NC_BADID' Bad ncid. `NC_ENOTNC4' Not a netCDF-4 file. `NC_ENOTVAR' Can't find this variable. `NC_ELATEDEF' This variable has already been the subject of a nc_enddef call. In netCDF-4 files nc_enddef will be called automatically for any data read or write. Once enddef has been called, it is impossible to set the checksum property for a variable. `NC_ENOTINDEFINE' Not in define mode. This is returned for netCDF classic or 64-bit offset files, or for netCDF-4 files, when they were been created with NC_STRICT_NC3 flag. (*note nc_create::). `NC_EPERM' Attempt to create object in read-only file. Example =======  File: netcdf-c.info, Node: nc_inq_var_fletcher32, Next: nc_def_var_endian, Prev: nc_def_var_fletcher32, Up: Variables 6.16 Learn About Checksum Parameters for a Variable: `nc_inq_var_fletcher32' ============================================================================ The function nc_inq_var_fletcher32 returns the checksum settings for a variable in a netCDF-4 file. Usage ===== nc_inq_var_fletcher32(int ncid, int varid, int *checksump); `ncid' NetCDF ID, from a previous call to nc_open or nc_create. `varid' Variable ID. `*checksump' If not-NULL, the nc_inq_var_fletcher32 function will set the int pointed at to NC_FLETCHER32 if the fletcher32 checksum filter is turned on for this variable, and NC_NOCHECKSUM if it is not. Errors ====== nc_inq_var_fletcher32 returns the value NC_NOERR if no errors occurred. Otherwise, the returned status indicates an error. Possible return codes include: `NC_NOERR' No error. `NC_BADID' Bad ncid. `NC_ENOTNC4' Not a netCDF-4 file. `NC_ENOTVAR' Can't find this variable. Example =======  File: netcdf-c.info, Node: nc_def_var_endian, Next: nc_inq_var_endian, Prev: nc_inq_var_fletcher32, Up: Variables 6.17 Define Endianness of a Variable: `nc_def_var_endian' ========================================================= The function nc_def_var_endian sets the endianness for a variable in a netCDF-4 file. This function must be called after the variable is defined, but before nc_enddef is called. By default, netCDF-4 variables are in native endianness. That is, they are big-endian on a big-endian machine, and little-endian on a little endian machine. In some cases a user might wish to change from native endianness to either big or little-endianness. This function allows them to do that. Usage ===== nc_def_var_endian(int ncid, int varid, int endian); `ncid' NetCDF ID, from a previous call to nc_open or nc_create. `varid' Variable ID. `endian' Set to NC_ENDIAN_NATIVE for native endianness. (This is the default). Set to NC_ENDIAN_LITTLE for little endian, or NC_ENDIAN_BIG for big endian. Errors ====== nc_def_var_endian returns the value NC_NOERR if no errors occurred. Otherwise, the returned status indicates an error. Possible return codes include: `NC_NOERR' No error. `NC_BADID' Bad ncid. `NC_ENOTNC4' Not a netCDF-4 file. `NC_ENOTVAR' Can't find this variable. `NC_ELATEDEF' This variable has already been the subject of a nc_enddef call. In netCDF-4 files nc_enddef will be called automatically for any data read or write. Once enddef has been called, it is impossible to set the endianness of a variable. `NC_ENOTINDEFINE' Not in define mode. This is returned for netCDF classic or 64-bit offset files, or for netCDF-4 files, when they were been created with NC_STRICT_NC3 flag, and the file is not in define mode. (*note nc_create::). `NC_EPERM' Attempt to create object in read-only file. Example =======  File: netcdf-c.info, Node: nc_inq_var_endian, Next: nc_inq_varid, Prev: nc_def_var_endian, Up: Variables 6.18 Learn About Endian Parameters for a Variable: `nc_inq_var_endian' ====================================================================== The function nc_inq_var_endian returns the endianness settings for a variable in a netCDF-4 file. Usage ===== nc_inq_var_endian(int ncid, int varid, int *endianp); `ncid' NetCDF ID, from a previous call to nc_open or nc_create. `varid' Variable ID. `*endianp' If not-NULL, the nc_inq_var_endian function will set the int pointed to this to NC_ENDIAN_LITTLE if this variable is stored in little-endian format, NC_ENDIAN_BIG if it is stored in big-endian format, and NC_ENDIAN_NATIVE if the endianness is not set, and the variable is not created yet. Errors ====== nc_inq_var_endian returns the value NC_NOERR if no errors occurred. Otherwise, the returned status indicates an error. Possible return codes include: `NC_NOERR' No error. `NC_BADID' Bad ncid. `NC_ENOTNC4' Not a netCDF-4 file. `NC_ENOTVAR' Can't find this variable. Example =======  File: netcdf-c.info, Node: nc_inq_varid, Next: nc_inq_var, Prev: nc_inq_var_endian, Up: Variables 6.19 Get a Variable ID from Its Name: nc_inq_varid ================================================== The function nc_inq_varid returns the ID of a netCDF variable, given its name. Usage ===== int nc_inq_varid (int ncid, const char *name, int *varidp); `ncid' NetCDF ID, from a previous call to nc_open or nc_create. `name' Variable name for which ID is desired. `varidp' Pointer to location for returned variable ID. Errors ====== nc_inq_varid returns the value NC_NOERR if no errors occurred. Otherwise, the returned status indicates an error. Possible causes of errors include: * The specified variable name is not a valid name for a variable in the specified netCDF dataset. * The specified netCDF ID does not refer to an open netCDF dataset. Example ======= Here is an example using nc_inq_varid to find out the ID of a variable named rh in an existing netCDF dataset named foo.nc: #include ... int status, ncid, rh_id; ... status = nc_open("foo.nc", NC_NOWRITE, &ncid); if (status != NC_NOERR) handle_error(status); ... status = nc_inq_varid (ncid, "rh", &rh_id); if (status != NC_NOERR) handle_error(status);  File: netcdf-c.info, Node: nc_inq_var, Next: nc_put_var1_ type, Prev: nc_inq_varid, Up: Variables 6.20 Get Information about a Variable from Its ID: nc_inq_var ============================================================= family &findex nc_inq_vardimid A family of functions that returns information about a netCDF variable, given its ID. Information about a variable includes its name, type, number of dimensions, a list of dimension IDs describing the shape of the variable, and the number of variable attributes that have been assigned to the variable. The function nc_inq_var returns all the information about a netCDF variable, given its ID. The other functions each return just one item of information about a variable. These other functions include nc_inq_varname, nc_inq_vartype, nc_inq_varndims, nc_inq_vardimid, and nc_inq_varnatts. Usage ===== int nc_inq_var (int ncid, int varid, char *name, nc_type *xtypep, int *ndimsp, int dimids[], int *nattsp); int nc_inq_varname (int ncid, int varid, char *name); int nc_inq_vartype (int ncid, int varid, nc_type *xtypep); int nc_inq_varndims (int ncid, int varid, int *ndimsp); int nc_inq_vardimid (int ncid, int varid, int dimids[]); int nc_inq_varnatts (int ncid, int varid, int *nattsp); `ncid' NetCDF ID, from a previous call to nc_open or nc_create. `varid' Variable ID. `name' Returned variable name. The caller must allocate space for the returned name. The maximum possible length, in characters, of a variable name is given by the predefined constant NC_MAX_NAME. (This doesn't include the null terminator, so declare your array to be size NC_MAX_NAME+1). The returned character array will be null-terminated. `xtypep' Pointer to location for returned variable type, one of the set of predefined netCDF external data types. The type of this parameter, nc_type, is defined in the netCDF header file. The valid netCDF external data types are NC_BYTE, NC_CHAR, NC_SHORT, NC_INT, NC_FLOAT, and NC_DOUBLE. `ndimsp' Pointer to location for returned number of dimensions the variable was defined as using. For example, 2 indicates a matrix, 1 indicates a vector, and 0 means the variable is a scalar with no dimensions. `dimids' Returned vector of *ndimsp dimension IDs corresponding to the variable dimensions. The caller must allocate enough space for a vector of at least *ndimsp integers to be returned. The maximum possible number of dimensions for a variable is given by the predefined constant NC_MAX_VAR_DIMS. `nattsp' Pointer to location for returned number of variable attributes assigned to this variable. These functions return the value NC_NOERR if no errors occurred. Otherwise, the returned status indicates an error. Possible causes of errors include: The variable ID is invalid for the specified netCDF dataset. The specified netCDF ID does not refer to an open netCDF dataset. Example ======= Here is an example using nc_inq_var to find out about a variable named rh in an existing netCDF dataset named foo.nc: #include ... int status /* error status */ int ncid; /* netCDF ID */ int rh_id; /* variable ID */ nc_type rh_type; /* variable type */ int rh_ndims; /* number of dims */ int rh_dimids[NC_MAX_VAR_DIMS]; /* dimension IDs */ int rh_natts /* number of attributes */ ... status = nc_open ("foo.nc", NC_NOWRITE, &ncid); if (status != NC_NOERR) handle_error(status); ... status = nc_inq_varid (ncid, "rh", &rh_id); if (status != NC_NOERR) handle_error(status); /* we don't need name, since we already know it */ status = nc_inq_var (ncid, rh_id, 0, &rh_type, &rh_ndims, rh_dimids, &rh_natts); if (status != NC_NOERR) handle_error(status);  File: netcdf-c.info, Node: nc_put_var1_ type, Next: nc_put_var_ type, Prev: nc_inq_var, Up: Variables 6.21 Write a Single Data Value: nc_put_var1_ TYPE ================================================= The functions nc_put_var1_ TYPE put a single data value of the specified type into a variable of an open netCDF dataset that is in data mode. Inputs are the netCDF ID, the variable ID, an index that specifies which value to add or alter, and the data value. The value is converted to the external data type of the variable, if necessary. The functions for types ubyte, ushort, uint, longlong, ulonglong, and string are only available for netCDF-4/HDF5 files. The nc_put_var1() function will write a variable of any type, including user defined type. For this function, the type of the data in memory must match the type of the variable - no data conversion is done. Usage ===== int nc_put_var1_text (int ncid, int varid, const size_t index[], const char *tp); int nc_put_var1_uchar (int ncid, int varid, const size_t index[], const unsigned char *up); int nc_put_var1_schar (int ncid, int varid, const size_t index[], const signed char *cp); int nc_put_var1_short (int ncid, int varid, const size_t index[], const short *sp); int nc_put_var1_int (int ncid, int varid, const size_t index[], const int *ip); int nc_put_var1_long (int ncid, int varid, const size_t index[], const long *lp); int nc_put_var1_float (int ncid, int varid, const size_t index[], const float *fp); int nc_put_var1_double(int ncid, int varid, const size_t index[], const double *dp); int nc_put_var1_ubyte (int ncid, int varid, const size_t index[], const unsigned char *up); int nc_put_var1_ushort(int ncid, int varid, const size_t index[], const unsigned short *sp); int nc_put_var1_uint (int ncid, int varid, const size_t index[], const unsigned int *ip); int nc_put_var1_longlong(int ncid, int varid, const size_t index[], const long long *ip); int nc_put_var1_ulonglong(int ncid, int varid, const size_t index[], const unsigned long long *ip); int nc_put_var1_string(int ncid, int varid, const size_t index[], const char **ip); int nc_put_var1(int ncid, int varid, const size_t *indexp, const void *op); `ncid' NetCDF ID, from a previous call to nc_open or nc_create. `varid' Variable ID. `index[]' The index of the data value to be written. The indices are relative to 0, so for example, the first data value of a two-dimensional variable would have index (0,0). The elements of index must correspond to the variable's dimensions. Hence, if the variable uses the unlimited dimension, the first index would correspond to the unlimited dimension. `tp' `up' `cp' `sp' `ip' `lp' `fp' `dp' Pointer to the data value to be written. If the type of data values differs from the netCDF variable type, type conversion will occur. *Note Type Conversion: (netcdf)Type Conversion. Return Codes ============ * NC_NOERR No error. * NC_EHDFERR Error reported by HDF5 layer. * NC_ENOTVAR The variable ID is invalid for the specified netCDF dataset. * NC_EINVALCOORDS The specified indices were out of range for the rank of the specified variable. For example, a negative index or an index that is larger than the corresponding dimension length will cause an error. * NC_ERANGE The specified value is out of the range of values representable by the external data type of the variable. (Does not apply to nc_put_var1() function). * NC_EINDEFINE The specified netCDF is in define mode rather than data mode. * NC_EBADID The specified netCDF ID does not refer to an open netCDF dataset. Example ======= Here is an example using nc_put_var1_double to set the (1,2,3) element of the variable named rh to 0.5 in an existing netCDF dataset named foo.nc. For simplicity in this example, we assume that we know that rh is dimensioned with time, lat, and lon, so we want to set the value of rh that corresponds to the second time value, the third lat value, and the fourth lon value: #include ... int status; /* error status */ int ncid; /* netCDF ID */ int rh_id; /* variable ID */ static size_t rh_index[] = {1, 2, 3}; /* where to put value */ static double rh_val = 0.5; /* value to put */ ... status = nc_open("foo.nc", NC_WRITE, &ncid); if (status != NC_NOERR) handle_error(status); ... status = nc_inq_varid (ncid, "rh", &rh_id); if (status != NC_NOERR) handle_error(status); ... status = nc_put_var1_double(ncid, rh_id, rh_index, &rh_val); if (status != NC_NOERR) handle_error(status);  File: netcdf-c.info, Node: nc_put_var_ type, Next: nc_put_vara_ type, Prev: nc_put_var1_ type, Up: Variables 6.22 Write an Entire Variable: nc_put_var_ TYPE =============================================== The nc_put_var_ TYPE family of functions write all the values of a variable into a netCDF variable of an open netCDF dataset. This is the simplest interface to use for writing a value in a scalar variable or whenever all the values of a multidimensional variable can all be written at once. The values to be written are associated with the netCDF variable by assuming that the last dimension of the netCDF variable varies fastest in the C interface. The values are converted to the external data type of the variable, if necessary. Take care when using the simplest forms of this interface with record variables when you don't specify how many records are to be written. If you try to write all the values of a record variable into a netCDF file that has no record data yet (hence has 0 records), nothing will be written. Similarly, if you try to write all of a record variable but there are more records in the file than you assume, more data may be written to the file than you supply, which may result in a segmentation violation. The functions for types ubyte, ushort, uint, longlong, ulonglong, and string are only available for netCDF-4/HDF5 files. The nc_put_var() function will write a variable of any type, including user defined type. For this function, the type of the data in memory must match the type of the variable - no data conversion is done. Usage ===== int nc_put_var_text (int ncid, int varid, const char *tp); int nc_put_var_uchar (int ncid, int varid, const unsigned char *up); int nc_put_var_schar (int ncid, int varid, const signed char *cp); int nc_put_var_short (int ncid, int varid, const short *sp); int nc_put_var_int (int ncid, int varid, const int *ip); int nc_put_var_long (int ncid, int varid, const long *lp); int nc_put_var_float (int ncid, int varid, const float *fp); int nc_put_var_double(int ncid, int varid, const double *dp); int nc_put_var_ubyte (int ncid, int varid, const unsigned char *op); int nc_put_var_ushort(int ncid, int varid, const unsigned short *op); int nc_put_var_uint (int ncid, int varid, const unsigned int *op); int nc_put_var_longlong (int ncid, int varid, const long long *op); int nc_put_var_ulonglong(int ncid, int varid, const unsigned long long *op); int nc_put_var_string(int ncid, int varid, const char **op); int nc_put_var (int ncid, int varid, const void *op); `ncid' NetCDF ID, from a previous call to nc_open or nc_create. `varid' Variable ID. `tp' `up' `cp' `sp' `ip' `lp' `fp' `dp' Pointer to a block of data values to be written. The order in which the data will be written to the netCDF variable is with the last dimension of the specified variable varying fastest. If the type of data values differs from the netCDF variable type, type conversion will occur. *Note Type Conversion: (netcdf)Type Conversion. Return Codes ============ * NC_NOERR The variable ID is invalid for the specified netCDF dataset. * NC_EHDFERR Error reported by HDF5 layer. * NC_ERANGE One or more of the specified values are out of the range of values representable by the external data type of the variable. (Does not apply to nc_put_var() function). * NC_EINDEFINE The specified netCDF dataset is in define mode rather than data mode. * NC_BADID The specified netCDF ID does not refer to an open netCDF dataset. * NC_ENOTVAR Bad variable ID. Example ======= Here is an example using nc_put_var_double to add or change all the values of the variable named rh to 0.5 in an existing netCDF dataset named foo.nc. For simplicity in this example, we assume that we know that rh is dimensioned with time, lat, and lon, and that there are three time values, five lat values, and ten lon values. #include ... #define TIMES 3 #define LATS 5 #define LONS 10 int status; /* error status */ int ncid; /* netCDF ID */ int rh_id; /* variable ID */ double rh_vals[TIMES*LATS*LONS]; /* array to hold values */ int i; ... status = nc_open("foo.nc", NC_WRITE, &ncid); if (status != NC_NOERR) handle_error(status); ... status = nc_inq_varid (ncid, "rh", &rh_id); if (status != NC_NOERR) handle_error(status); ... for (i = 0; i < TIMES*LATS*LONS; i++) rh_vals[i] = 0.5; /* write values into netCDF variable */ status = nc_put_var_double(ncid, rh_id, rh_vals); if (status != NC_NOERR) handle_error(status);  File: netcdf-c.info, Node: nc_put_vara_ type, Next: nc_put_vars_ type, Prev: nc_put_var_ type, Up: Variables 6.23 Write an Array of Values: nc_put_vara_ TYPE ================================================ The function nc_put_vara_ TYPE writes values into a netCDF variable of an open netCDF dataset. The part of the netCDF variable to write is specified by giving a corner and a vector of edge lengths that refer to an array section of the netCDF variable. The values to be written are associated with the netCDF variable by assuming that the last dimension of the netCDF variable varies fastest in the C interface. The netCDF dataset must be in data mode. The functions for types ubyte, ushort, uint, longlong, ulonglong, and string are only available for netCDF-4/HDF5 files. The nc_put_var() function will write a variable of any type, including user defined type. For this function, the type of the data in memory must match the type of the variable - no data conversion is done. Usage ===== int nc_put_vara_ type (int ncid, int varid, const size_t start[], const size_t count[], const type *valuesp); int nc_put_vara_text (int ncid, int varid, const size_t start[], const size_t count[], const char *tp); int nc_put_vara_uchar (int ncid, int varid, const size_t start[], const size_t count[], const unsigned char *up); int nc_put_vara_schar (int ncid, int varid, const size_t start[], const size_t count[], const signed char *cp); int nc_put_vara_short (int ncid, int varid, const size_t start[], const size_t count[], const short *sp); int nc_put_vara_int (int ncid, int varid, const size_t start[], const size_t count[], const int *ip); int nc_put_vara_long (int ncid, int varid, const size_t start[], const size_t count[], const long *lp); int nc_put_vara_float (int ncid, int varid, const size_t start[], const size_t count[], const float *fp); int nc_put_vara_double(int ncid, int varid, const size_t start[], const size_t count[], const double *dp); int nc_put_vara_ubyte (int ncid, int varid, const size_t *startp, const size_t *countp, const unsigned char *op); int nc_put_vara_ushort(int ncid, int varid, const size_t *startp, const size_t *countp, const unsigned short *op); int nc_put_vara_uint (int ncid, int varid, const size_t *startp, const size_t *countp, const unsigned int *op); int nc_put_vara_longlong (int ncid, int varid, const size_t *startp, const size_t *countp, const long long *op); int nc_put_vara_ulonglong(int ncid, int varid, const size_t *startp, const size_t *countp, const unsigned long long *op); int nc_put_vara_string(int ncid, int varid, const size_t *startp, const size_t *countp, const char **op); int nc_put_vara (int ncid, int varid, const size_t *startp, const size_t *countp, const void *op); `ncid' NetCDF ID, from a previous call to nc_open or nc_create. `varid' Variable ID. `start' A vector of size_t integers specifying the index in the variable where the first of the data values will be written. The indices are relative to 0, so for example, the first data value of a variable would have index (0, 0, ... , 0). The size of start must be the same as the number of dimensions of the specified variable. The elements of start must correspond to the variable's dimensions in order. Hence, if the variable is a record variable, the first index would correspond to the starting record number for writing the data values. `count' A vector of size_t integers specifying the edge lengths along each dimension of the block of data values to be written. To write a single value, for example, specify count as (1, 1, ... , 1). The length of count is the number of dimensions of the specified variable. The elements of count correspond to the variable's dimensions. Hence, if the variable is a record variable, the first element of count corresponds to a count of the number of records to write. Note: setting any element of the count array to zero causes the function to exit without error, and without doing anything. `tp' `up' `cp' `sp' `ip' `lp' `fp' `dp' Pointer to a block of data values to be written. The order in which the data will be written to the netCDF variable is with the last dimension of the specified variable varying fastest. If the type of data values differs from the netCDF variable type, type conversion will occur. *Note Type Conversion: (netcdf)Type Conversion. Return Codes ============ * NC_NOERR No error. * NC_EHDFERR Error reported by HDF5 layer. * NC_ENOTVAR The variable ID is invalid for the specified netCDF dataset. * NC_EINVALCOORDS The specified corner indices were out of range for the rank of the specified variable. For example, a negative index, or an index that is larger than the corresponding dimension length will cause an error. * NC_EEDGE The specified edge lengths added to the specified corner would have referenced data out of range for the rank of the specified variable. For example, an edge length that is larger than the corresponding dimension length minus the corner index will cause an error. * NC_ERANGE One or more of the specified values are out of the range of values representable by the external data type of the variable. (Does not apply to the nc_put_vara() function). * NC_EINDEFINE The specified netCDF dataset is in define mode rather than data mode. * NC_EBADID The specified netCDF ID does not refer to an open netCDF dataset. * NC_ECHAR Attempt to convert to or from char. * NC_ENOMEM Out of memory. * NC_EBADTYPE Bad type. Example ======= Here is an example using nc_put_vara_double to add or change all the values of the variable named rh to 0.5 in an existing netCDF dataset named foo.nc. For simplicity in this example, we assume that we know that rh is dimensioned with time, lat, and lon, and that there are three time values, five lat values, and ten lon values. #include ... #define TIMES 3 #define LATS 5 #define LONS 10 int status; /* error status */ int ncid; /* netCDF ID */ int rh_id; /* variable ID */ static size_t start[] = {0, 0, 0}; /* start at first value */ static size_t count[] = {TIMES, LATS, LONS}; double rh_vals[TIMES*LATS*LONS]; /* array to hold values */ int i; ... status = nc_open("foo.nc", NC_WRITE, &ncid); if (status != NC_NOERR) handle_error(status); ... status = nc_inq_varid (ncid, "rh", &rh_id); if (status != NC_NOERR) handle_error(status); ... for (i = 0; i < TIMES*LATS*LONS; i++) rh_vals[i] = 0.5; /* write values into netCDF variable */ status = nc_put_vara_double(ncid, rh_id, start, count, rh_vals); if (status != NC_NOERR) handle_error(status);  File: netcdf-c.info, Node: nc_put_vars_ type, Next: nc_put_varm_ type, Prev: nc_put_vara_ type, Up: Variables 6.24 Write a Subsampled Array of Values: nc_put_vars_ TYPE ========================================================== Each member of the family of functions nc_put_vars_ TYPE writes a subsampled (strided) array section of values into a netCDF variable of an open netCDF dataset. The subsampled array section is specified by giving a corner, a vector of counts, and a stride vector. The netCDF dataset must be in data mode. The functions for types ubyte, ushort, uint, longlong, ulonglong, and string are only available for netCDF-4/HDF5 files. The nc_put_vars() function will write a variable of any type, including user defined type. For this function, the type of the data in memory must match the type of the variable - no data conversion is done. Usage ===== int nc_put_vars_text (int ncid, int varid, const size_t start[], const size_t count[], const ptrdiff_t stride[], const char *tp); int nc_put_vars_uchar (int ncid, int varid, const size_t start[], const size_t count[], const ptrdiff_t stride[], const unsigned char *up); int nc_put_vars_schar (int ncid, int varid, const size_t start[], const size_t count[], const ptrdiff_t stride[], const signed char *cp); int nc_put_vars_short (int ncid, int varid, const size_t start[], const size_t count[], const ptrdiff_t stride[], const short *sp); int nc_put_vars_int (int ncid, int varid, const size_t start[], const size_t count[], const ptrdiff_t stride[], const int *ip); int nc_put_vars_long (int ncid, int varid, const size_t start[], const size_t count[], const ptrdiff_t stride[], const long *lp); int nc_put_vars_float (int ncid, int varid, const size_t start[], const size_t count[], const ptrdiff_t stride[], const float *fp); int nc_put_vars_double(int ncid, int varid, const size_t start[], const size_t count[], const ptrdiff_t stride[], const double *dp); int nc_put_vars_ubyte (int ncid, int varid, const size_t *startp, const size_t *countp, const ptrdiff_t *stridep, const unsigned char *op); int nc_put_vars_ushort(int ncid, int varid, const size_t *startp, const size_t *countp, const ptrdiff_t *stridep, const unsigned short *op); int nc_put_vars_uint (int ncid, int varid, const size_t *startp, const size_t *countp, const ptrdiff_t *stridep, const unsigned int *op); int nc_put_vars_longlong (int ncid, int varid, const size_t *startp, const size_t *countp, const ptrdiff_t *stridep, const long long *op); int nc_put_vars_ulonglong(int ncid, int varid, const size_t *startp, const size_t *countp, const ptrdiff_t *stridep, const unsigned long long *op); int nc_put_vars_string(int ncid, int varid, const size_t *startp, const size_t *countp, const ptrdiff_t *stridep, const char **op); int nc_put_vars (int ncid, int varid, const size_t *startp, const size_t *countp, const ptrdiff_t *stridep, const void *op); `ncid' NetCDF ID, from a previous call to nc_open or nc_create. `varid' Variable ID. `start' A vector of size_t integers specifying the index in the variable where the first of the data values will be written. The indices are relative to 0, so for example, the first data value of a variable would have index (0, 0, ... , 0). The elements of start correspond, in order, to the variable's dimensions. Hence, if the variable is a record variable, the first index corresponds to the starting record number for writing the data values. `count' A vector of size_t integers specifying the number of indices selected along each dimension. To write a single value, for example, specify count as (1, 1, ... , 1). The elements of count correspond, in order, to the variable's dimensions. Hence, if the variable is a record variable, the first element of count corresponds to a count of the number of records to write. Note: setting any element of the count array to zero causes the function to exit without error, and without doing anything. `stride' A vector of ptrdiff_t integers that specifies the sampling interval along each dimension of the netCDF variable. The elements of the stride vector correspond, in order, to the netCDF variable's dimensions (stride[0] gives the sampling interval along the most slowly varying dimension of the netCDF variable). Sampling intervals are specified in type-independent units of elements (a value of 1 selects consecutive elements of the netCDF variable along the corresponding dimension, a value of 2 selects every other element, etc.). A NULL stride argument is treated as (1, 1, ... , 1). `tp' `up' `cp' `sp' `ip' `lp' `fp' `dp' Pointer to a block of data values to be written. The order in which the data will be written to the netCDF variable is with the last dimension of the specified variable varying fastest. If the type of data values differs from the netCDF variable type, type conversion will occur. *Note Type Conversion: (netcdf)Type Conversion. Return Codes ============ * NC_NOERR No error. * NC_EHDFERR Error reported by HDF5 layer. * NC_ENOTVAR The variable ID is invalid for the specified netCDF dataset. * NC_EINVALCOORDS The specified corner indices were out of range for the rank of the specified variable. For example, a negative index, or an index that is larger than the corresponding dimension length will cause an error. * NC_EEDGE The specified edge lengths added to the specified corner would have referenced data out of range for the rank of the specified variable. For example, an edge length that is larger than the corresponding dimension length minus the corner index will cause an error. * NC_ERANGE One or more of the specified values are out of the range of values representable by the external data type of the variable. (Does not apply to the nc_put_vars() function). * NC_EINDEFINE The specified netCDF dataset is in define mode rather than data mode. * NC_EBADID The specified netCDF ID does not refer to an open netCDF dataset. * NC_ECHAR Attempt to convert to or from char. * NC_ENOMEM Out of memory. * NC_EBADTYPE Bad type. Example ======= Here is an example of using nc_put_vars_float to write - from an internal array - every other point of a netCDF variable named rh which is described by the C declaration float rh[4][6] (note the size of the dimensions): #include ... #define NDIM 2 /* rank of netCDF variable */ int ncid; /* netCDF ID */ int status; /* error status */ int rhid; /* variable ID */ static size_t start[NDIM] /* netCDF variable start point: */ = {0, 0}; /* first element */ static size_t count[NDIM] /* size of internal array: entire */ = {2, 3}; /* (subsampled) netCDF variable */ static ptrdiff_t stride[NDIM] /* variable subsampling intervals: */ = {2, 2}; /* access every other netCDF element */ float rh[2][3]; /* note subsampled sizes for */ /* netCDF variable dimensions */ ... status = nc_open("foo.nc", NC_WRITE, &ncid); if (status != NC_NOERR) handle_error(status); ... status = nc_inq_varid(ncid, "rh", &rhid); if (status != NC_NOERR) handle_error(status); ... status = nc_put_vars_float(ncid, rhid, start, count, stride, rh); if (status != NC_NOERR) handle_error(status);  File: netcdf-c.info, Node: nc_put_varm_ type, Next: nc_get_var1_ type, Prev: nc_put_vars_ type, Up: Variables 6.25 Write a Mapped Array of Values: nc_put_varm_ TYPE ====================================================== The nc_put_varm_ TYPE family of functions writes a mapped array section of values into a netCDF variable of an open netCDF dataset. The mapped array section is specified by giving a corner, a vector of counts, a stride vector, and an index mapping vector. The index mapping vector is a vector of integers that specifies the mapping between the dimensions of a netCDF variable and the in-memory structure of the internal data array. No assumptions are made about the ordering or length of the dimensions of the data array. The netCDF dataset must be in data mode. The functions for types ubyte, ushort, uint, longlong, ulonglong, and string are only available for netCDF-4/HDF5 files. The nc_put_varm() function will write a variable of any type, including user defined type. For this function, the type of the data in memory must match the type of the variable - no data conversion is done. Usage ===== int nc_put_varm_text (int ncid, int varid, const size_t start[], const size_t count[], const ptrdiff_t stride[], const ptrdiff_t imap[], const char *tp); int nc_put_varm_uchar (int ncid, int varid, const size_t start[], const size_t count[], const ptrdiff_t stride[], const ptrdiff_t imap[], const unsigned char *up); int nc_put_varm_schar (int ncid, int varid, const size_t start[], const size_t count[], const ptrdiff_t stride[], const ptrdiff_t imap[], const signed char *cp); int nc_put_varm_short (int ncid, int varid, const size_t start[], const size_t count[], const ptrdiff_t stride[], const ptrdiff_t imap[], const short *sp); int nc_put_varm_int (int ncid, int varid, const size_t start[], const size_t count[], const ptrdiff_t stride[], const ptrdiff_t imap[], const int *ip); int nc_put_varm_long (int ncid, int varid, const size_t start[], const size_t count[], const ptrdiff_t stride[], const ptrdiff_t imap[], const long *lp); int nc_put_varm_float (int ncid, int varid, const size_t start[], const size_t count[], const ptrdiff_t stride[], const ptrdiff_t imap[], const float *fp); int nc_put_varm_double(int ncid, int varid, const size_t start[], const size_t count[], const ptrdiff_t stride[], const ptrdiff_t imap[], const double *dp); int nc_put_varm_ubyte (int ncid, int varid, const size_t *startp, const size_t *countp, const ptrdiff_t *stridep, const ptrdiff_t * imapp, const unsigned char *op); int nc_put_varm_ushort(int ncid, int varid, const size_t *startp, const size_t *countp, const ptrdiff_t *stridep, const ptrdiff_t * imapp, const unsigned short *op); int nc_put_varm_uint (int ncid, int varid, const size_t *startp, const size_t *countp, const ptrdiff_t *stridep, const ptrdiff_t * imapp, const unsigned int *op); int nc_put_varm_longlong (int ncid, int varid, const size_t *startp, const size_t *countp, const ptrdiff_t *stridep, const ptrdiff_t * imapp, const long long *op); int nc_put_varm_ulonglong(int ncid, int varid, const size_t *startp, const size_t *countp, const ptrdiff_t *stridep, const ptrdiff_t * imapp, const unsigned long long *op); int nc_put_varm_string(int ncid, int varid, const size_t *startp, const size_t *countp, const ptrdiff_t *stridep, const ptrdiff_t * imapp, const char **op); int nc_put_varm (int ncid, int varid, const size_t *startp, const size_t *countp, const ptrdiff_t *stridep, const ptrdiff_t *imapp, const void *op); n `ncid' NetCDF ID, from a previous call to nc_open or nc_create. `varid' Variable ID. `start' A vector of size_t integers specifying the index in the variable where the first of the data values will be written. The indices are relative to 0, so for example, the first data value of a variable would have index (0, 0, ... , 0). The elements of start correspond, in order, to the variable's dimensions. Hence, if the variable is a record variable, the first index corresponds to the starting record number for writing the data values. `count' A vector of size_t integers specifying the number of indices selected along each dimension. To write a single value, for example, specify count as (1, 1, ... , 1). The elements of count correspond, in order, to the variable's dimensions. Hence, if the variable is a record variable, the first element of count corresponds to a count of the number of records to write. Note: setting any element of the count array to zero causes the function to exit without error, and without doing anything. `stride' A vector of ptrdiff_t integers that specifies the sampling interval along each dimension of the netCDF variable. The elements of the stride vector correspond, in order, to the netCDF variable's dimensions (stride[0] gives the sampling interval along the most slowly varying dimension of the netCDF variable). Sampling intervals are specified in type-independent units of elements (a value of 1 selects consecutive elements of the netCDF variable along the corresponding dimension, a value of 2 selects every other element, etc.). A NULL stride argument is treated as (1, 1, ... , 1). `imap' A vector of ptrdiff_t integers that specifies the mapping between the dimensions of a netCDF variable and the in-memory structure of the internal data array. The elements of the index mapping vector correspond, in order, to the netCDF variable's dimensions (imap[0] gives the distance between elements of the internal array corresponding to the most slowly varying dimension of the netCDF variable). Distances between elements are specified in type-independent units of elements (the distance between internal elements that occupy adjacent memory locations is 1 and not the element's byte-length as in netCDF 2). A NULL argument means the memory-resident values have the same structure as the associated netCDF variable. `tp' `up' `cp' `sp' `ip' `lp' `fp' `dp' Pointer to the location used for computing where the data values will be found; the data should be of the type appropriate for the function called. If the type of data values differs from the netCDF variable type, type conversion will occur. *Note Type Conversion: (netcdf)Type Conversion. Return Codes ============ * NC_NOERR No error. * NC_EHDFERR Error reported by HDF5 layer. * NC_ENOTVAR The variable ID is invalid for the specified netCDF dataset. * NC_EINVALCOORDS The specified corner indices were out of range for the rank of the specified variable. For example, a negative index, or an index that is larger than the corresponding dimension length will cause an error. * NC_EEDGE The specified edge lengths added to the specified corner would have referenced data out of range for the rank of the specified variable. For example, an edge length that is larger than the corresponding dimension length minus the corner index will cause an error. * NC_ERANGE One or more of the specified values are out of the range of values representable by the external data type of the variable. (Does not apply to the nc_put_vars() function). * NC_EINDEFINE The specified netCDF dataset is in define mode rather than data mode. * NC_EBADID The specified netCDF ID does not refer to an open netCDF dataset. * NC_ECHAR Attempt to convert to or from char. * NC_ENOMEM Out of memory. Example ======= The following imap vector maps in the trivial way a 4x3x2 netCDF variable and an internal array of the same shape: float a[4][3][2]; /* same shape as netCDF variable */ int imap[3] = {6, 2, 1}; /* netCDF dimension inter-element distance */ /* ---------------- ---------------------- */ /* most rapidly varying 1 */ /* intermediate 2 (=imap[2]*2) */ /* most slowly varying 6 (=imap[1]*3) */ Using the imap vector above with nc_put_varm_float obtains the same result as simply using nc_put_var_float. Here is an example of using nc_put_varm_float to write - from a transposed, internal array - a netCDF variable named rh which is described by the C declaration float rh[6][4] (note the size and order of the dimensions): #include ... #define NDIM 2 /* rank of netCDF variable */ int ncid; /* netCDF ID */ int status; /* error status */ int rhid; /* variable ID */ static size_t start[NDIM] /* netCDF variable start point: */ = {0, 0}; /* first element */ static size_t count[NDIM] /* size of internal array: entire netCDF */ = {6, 4}; /* variable; order corresponds to netCDF */ /* variable -- not internal array */ static ptrdiff_t stride[NDIM]/* variable subsampling intervals: */ = {1, 1}; /* sample every netCDF element */ static ptrdiff_t imap[NDIM] /* internal array inter-element distances; */ = {1, 6}; /* would be {4, 1} if not transposing */ float rh[4][6]; /* note transposition of netCDF variable */ /* dimensions */ ... status = nc_open("foo.nc", NC_WRITE, &ncid); if (status != NC_NOERR) handle_error(status); ... status = nc_inq_varid(ncid, "rh", &rhid); if (status != NC_NOERR) handle_error(status); ... status = nc_put_varm_float(ncid, rhid, start, count, stride, imap, rh); if (status != NC_NOERR) handle_error(status); Here is another example of using nc_put_varm_float to write - from a transposed, internal array - a subsample of the same netCDF variable, by writing every other point of the netCDF variable: #include ... #define NDIM 2 /* rank of netCDF variable */ int ncid; /* netCDF ID */ int status; /* error status */ int rhid; /* variable ID */ static size_t start[NDIM] /* netCDF variable start point: */ = {0, 0}; /* first element */ static size_t count[NDIM] /* size of internal array: entire */ = {3, 2}; /* (subsampled) netCDF variable; order of */ /* dimensions corresponds to netCDF */ /* variable -- not internal array */ static ptrdiff_t stride[NDIM] /* variable subsampling intervals: */ = {2, 2}; /* sample every other netCDF element */ static ptrdiff_t imap[NDIM] /* internal array inter-element distances; */ = {1, 3}; /* would be {2, 1} if not transposing */ float rh[2][3]; /* note transposition of (subsampled) */ /* netCDF variable dimensions */ ... status = nc_open("foo.nc", NC_WRITE, &ncid); if (status != NC_NOERR) handle_error(status); ... status = nc_inq_varid(ncid, "rh", &rhid); if (status != NC_NOERR) handle_error(status); ... status = nc_put_varm_float(ncid, rhid, start, count, stride, imap, rh); if (status != NC_NOERR) handle_error(status);  File: netcdf-c.info, Node: nc_get_var1_ type, Next: nc_get_var_ type, Prev: nc_put_varm_ type, Up: Variables 6.26 Read a Single Data Value: nc_get_var1_ TYPE ================================================ The functions nc_get_var1_ TYPE get a single data value from a variable of an open netCDF dataset that is in data mode. Inputs are the netCDF ID, the variable ID, a multidimensional index that specifies which value to get, and the address of a location into which the data value will be read. The value is converted from the external data type of the variable, if necessary. The functions for types ubyte, ushort, uint, longlong, ulonglong, and string are only available for netCDF-4/HDF5 files. The nc_get_var1() function will read a variable of any type, including user defined type. For this function, the type of the data in memory must match the type of the variable - no data conversion is done. Usage ===== int nc_get_var1_text (int ncid, int varid, const size_t index[], char *tp); int nc_get_var1_uchar (int ncid, int varid, const size_t index[], unsigned char *up); int nc_get_var1_schar (int ncid, int varid, const size_t index[], signed char *cp); int nc_get_var1_short (int ncid, int varid, const size_t index[], short *sp); int nc_get_var1_int (int ncid, int varid, const size_t index[], int *ip); int nc_get_var1_long (int ncid, int varid, const size_t index[], long *lp); int nc_get_var1_float (int ncid, int varid, const size_t index[], float *fp); int nc_get_var1_double(int ncid, int varid, const size_t index[], double *dp); int nc_get_var1_ubyte (int ncid, int varid, const size_t *indexp, unsigned char *ip); int nc_get_var1_ushort(int ncid, int varid, const size_t *indexp, unsigned short *ip); int nc_get_var1_uint (int ncid, int varid, const size_t *indexp, unsigned int *ip); int nc_get_var1_longlong (int ncid, int varid, const size_t *indexp, long long *ip); int nc_get_var1_ulonglong(int ncid, int varid, const size_t *indexp, unsigned long long *ip); int nc_get_var1_string(int ncid, int varid, const size_t *indexp, char **ip); int nc_get_var1 (int ncid, int varid, const size_t *indexp, void *ip); `ncid' NetCDF ID, from a previous call to nc_open or nc_create. `varid' Variable ID. `index[]' The index of the data value to be read. The indices are relative to 0, so for example, the first data value of a two-dimensional variable would have index (0,0). The elements of index must correspond to the variable's dimensions. Hence, if the variable is a record variable, the first index is the record number. `tp' `up' `cp' `sp' `ip' `lp' `fp' `dp' Pointer to the location into which the data value is read. If the type of data value differs from the netCDF variable type, type conversion will occur. *Note Type Conversion: (netcdf)Type Conversion. Return Codes ============ * NC_NOERR No error. * NC_EHDFERR Error reported by HDF5 layer. * NC_ENOTVAR The variable ID is invalid for the specified netCDF dataset. * NC_EINVALCOORDS The specified corner indices were out of range for the rank of the specified variable. For example, a negative index, or an index that is larger than the corresponding dimension length will cause an error. * NC_EEDGE The specified edge lengths added to the specified corner would have referenced data out of range for the rank of the specified variable. For example, an edge length that is larger than the corresponding dimension length minus the corner index will cause an error. * NC_ERANGE One or more of the specified values are out of the range of values representable by the external data type of the variable. (Does not apply to the nc_put_vars() function). * NC_EINDEFINE The specified netCDF is in define mode rather than data mode. * NC_EBADID The specified netCDF ID does not refer to an open netCDF dataset. * NC_ECHAR Attempt to convert to or from char. * NC_ENOMEM Out of memory. Example ======= Here is an example using nc_get_var1_double to get the (1,2,3) element of the variable named rh in an existing netCDF dataset named foo.nc. For simplicity in this example, we assume that we know that rh is dimensioned with time, lat, and lon, so we want to get the value of rh that corresponds to the second time value, the third lat value, and the fourth lon value: #include ... int status; /* error status */ int ncid; /* netCDF ID */ int rh_id; /* variable ID */ static size_t rh_index[] = {1, 2, 3}; /* where to get value from */ double rh_val; /* where to put it */ ... status = nc_open("foo.nc", NC_NOWRITE, &ncid); if (status != NC_NOERR) handle_error(status); ... status = nc_inq_varid (ncid, "rh", &rh_id); if (status != NC_NOERR) handle_error(status); ... status = nc_get_var1_double(ncid, rh_id, rh_index, &rh_val); if (status != NC_NOERR) handle_error(status);  File: netcdf-c.info, Node: nc_get_var_ type, Next: nc_get_vara_ type, Prev: nc_get_var1_ type, Up: Variables 6.27 Read an Entire Variable nc_get_var_ TYPE ============================================= The members of the nc_get_var_ TYPE family of functions read all the values from a netCDF variable of an open netCDF dataset. This is the simplest interface to use for reading the value of a scalar variable or when all the values of a multidimensional variable can be read at once. The values are read into consecutive locations with the last dimension varying fastest. The netCDF dataset must be in data mode. Take care when using the simplest forms of this interface with record variables when you don't specify how many records are to be read. If you try to read all the values of a record variable into an array but there are more records in the file than you assume, more data will be read than you expect, which may cause a segmentation violation. The functions for types ubyte, ushort, uint, longlong, ulonglong, and string are only available for netCDF-4/HDF5 files. The nc_get_var() function will read a variable of any type, including user defined type. For this function, the type of the data in memory must match the type of the variable - no data conversion is done. Usage ===== int nc_get_var_text (int ncid, int varid, char *tp); int nc_get_var_uchar (int ncid, int varid, unsigned char *up); int nc_get_var_schar (int ncid, int varid, signed char *cp); int nc_get_var_short (int ncid, int varid, short *sp); int nc_get_var_int (int ncid, int varid, int *ip); int nc_get_var_long (int ncid, int varid, long *lp); int nc_get_var_float (int ncid, int varid, float *fp); int nc_get_var_double(int ncid, int varid, double *dp); int nc_get_var_ubyte (int ncid, int varid, unsigned char *ip); int nc_get_var_ushort(int ncid, int varid, unsigned short *ip); int nc_get_var_uint (int ncid, int varid, unsigned int *ip); int nc_get_var_longlong (int ncid, int varid, long long *ip); int nc_get_var_ulonglong(int ncid, int varid, unsigned long long *ip); int nc_get_var_string(int ncid, int varid, char **ip); int nc_get_var (int ncid, int varid, void *ip); `ncid' NetCDF ID, from a previous call to nc_open or nc_create. `varid' Variable ID. `tp' `up' `cp' `sp' `ip' `lp' `fp' `dp' Pointer to the location into which the data value is read. If the type of data value differs from the netCDF variable type, type conversion will occur. *Note Type Conversion: (netcdf)Type Conversion. Return Codes ============ * NC_NOERR No error. * NC_EHDFERR Error reported by HDF5 layer. * NC_ENOTVAR The variable ID is invalid for the specified netCDF dataset. * NC_EINVALCOORDS The specified corner indices were out of range for the rank of the specified variable. For example, a negative index, or an index that is larger than the corresponding dimension length will cause an error. * NC_EEDGE The specified edge lengths added to the specified corner would have referenced data out of range for the rank of the specified variable. For example, an edge length that is larger than the corresponding dimension length minus the corner index will cause an error. * NC_ERANGE One or more of the specified values are out of the range of values representable by the external data type of the variable. (Does not apply to the nc_put_vars() function). * NC_EINDEFINE The specified netCDF is in define mode rather than data mode. * NC_EBADID The specified netCDF ID does not refer to an open netCDF dataset. * NC_ECHAR Attempt to convert to or from char. * NC_ENOMEM Out of memory. Example ======= Here is an example using nc_get_var_double to read all the values of the variable named rh from an existing netCDF dataset named foo.nc. For simplicity in this example, we assume that we know that rh is dimensioned with time, lat, and lon, and that there are three time values, five lat values, and ten lon values. #include ... #define TIMES 3 #define LATS 5 #define LONS 10 int status; /* error status */ int ncid; /* netCDF ID */ int rh_id; /* variable ID */ double rh_vals[TIMES*LATS*LONS]; /* array to hold values */ ... status = nc_open("foo.nc", NC_NOWRITE, &ncid); if (status != NC_NOERR) handle_error(status); ... status = nc_inq_varid (ncid, "rh", &rh_id); if (status != NC_NOERR) handle_error(status); ... /* read values from netCDF variable */ status = nc_get_var_double(ncid, rh_id, rh_vals); if (status != NC_NOERR) handle_error(status);  File: netcdf-c.info, Node: nc_get_vara_ type, Next: nc_get_vars_ type, Prev: nc_get_var_ type, Up: Variables 6.28 Read an Array of Values: nc_get_vara_ TYPE =============================================== The members of the nc_get_vara_ TYPE family of functions read an array of values from a netCDF variable of an open netCDF dataset. The array is specified by giving a corner and a vector of edge lengths. The values are read into consecutive locations with the last dimension varying fastest. The netCDF dataset must be in data mode. The functions for types ubyte, ushort, uint, longlong, ulonglong, and string are only available for netCDF-4/HDF5 files. The nc_get_vara() function will write a variable of any type, including user defined type. For this function, the type of the data in memory must match the type of the variable - no data conversion is done. Usage ===== int nc_get_vara_text (int ncid, int varid, const size_t start[], const size_t count[], char *tp); int nc_get_vara_uchar (int ncid, int varid, const size_t start[], const size_t count[], unsigned char *up); int nc_get_vara_schar (int ncid, int varid, const size_t start[], const size_t count[], signed char *cp); int nc_get_vara_short (int ncid, int varid, const size_t start[], const size_t count[], short *sp); int nc_get_vara_int (int ncid, int varid, const size_t start[], const size_t count[], int *ip); int nc_get_vara_long (int ncid, int varid, const size_t start[], const size_t count[], long *lp); int nc_get_vara_float (int ncid, int varid, const size_t start[], const size_t count[], float *fp); int nc_get_vara_double(int ncid, int varid, const size_t start[], const size_t count[], double *dp); int nc_get_vara_ubyte (int ncid, int varid, const size_t *startp, const size_t *countp, unsigned char *ip); int nc_get_vara_ushort(int ncid, int varid, const size_t *startp, const size_t *countp, unsigned short *ip); int nc_get_vara_uint (int ncid, int varid, const size_t *startp, const size_t *countp, unsigned int *ip); int nc_get_vara_longlong(int ncid, int varid, const size_t *startp, const size_t *countp, long long *ip); int nc_get_vara_ulonglong(int ncid, int varid, const size_t *startp, const size_t *countp, unsigned long long *ip); int nc_get_vara_string(int ncid, int varid, const size_t *startp, const size_t *countp, char **ip); int nc_get_vara (int ncid, int varid, const size_t start[], const size_t count[], void *ip); `ncid' NetCDF ID, from a previous call to nc_open or nc_create. `varid' Variable ID. `start' A vector of size_t integers specifying the index in the variable where the first of the data values will be read. The indices are relative to 0, so for example, the first data value of a variable would have index (0, 0, ... , 0). The length of start must be the same as the number of dimensions of the specified variable. The elements of start correspond, in order, to the variable's dimensions. Hence, if the variable is a record variable, the first index would correspond to the starting record number for reading the data values. `count' A vector of size_t integers specifying the edge lengths along each dimension of the block of data values to be read. To read a single value, for example, specify count as (1, 1, ... , 1). The length of count is the number of dimensions of the specified variable. The elements of count correspond, in order, to the variable's dimensions. Hence, if the variable is a record variable, the first element of count corresponds to a count of the number of records to read. Note: setting any element of the count array to zero causes the function to exit without error, and without doing anything. `tp' `up' `cp' `sp' `ip' `lp' `fp' `dp' Pointer to the location into which the data value is read. If the type of data value differs from the netCDF variable type, type conversion will occur. *Note Type Conversion: (netcdf)Type Conversion. Return Codes ============ * NC_NOERR No error. * NC_ENOTVAR The variable ID is invalid for the specified netCDF dataset. * NC_EINVALCOORDS The specified corner indices were out of range for the rank of the specified variable. For example, a negative index or an index that is larger than the corresponding dimension length will cause an error. * NC_EEDGE The specified edge lengths added to the specified corner would have referenced data out of range for the rank of the specified variable. For example, an edge length that is larger than the corresponding dimension length minus the corner index will cause an error. * NC_ERANGE One or more of the values are out of the range of values representable by the desired type. (Does not apply to nc_get_vara() function). * NC_EINDEFINE The specified netCDF is in define mode rather than data mode. * NC_EBADID The specified netCDF ID does not refer to an open netCDF dataset. Example ======= Here is an example using nc_get_vara_double to read all the values of the variable named rh from an existing netCDF dataset named foo.nc. For simplicity in this example, we assume that we know that rh is dimensioned with time, lat, and lon, and that there are three time values, five lat values, and ten lon values. #include ... #define TIMES 3 #define LATS 5 #define LONS 10 int status; /* error status */ int ncid; /* netCDF ID */ int rh_id; /* variable ID */ static size_t start[] = {0, 0, 0}; /* start at first value */ static size_t count[] = {TIMES, LATS, LONS}; double rh_vals[TIMES*LATS*LONS]; /* array to hold values */ ... status = nc_open("foo.nc", NC_NOWRITE, &ncid); if (status != NC_NOERR) handle_error(status); ... status = nc_inq_varid (ncid, "rh", &rh_id); if (status != NC_NOERR) handle_error(status); ... /* read values from netCDF variable */ status = nc_get_vara_double(ncid, rh_id, start, count, rh_vals); if (status != NC_NOERR) handle_error(status);  File: netcdf-c.info, Node: nc_get_vars_ type, Next: nc_get_varm_ type, Prev: nc_get_vara_ type, Up: Variables 6.29 Read a Subsampled Array of Values: nc_get_vars_ TYPE ========================================================= The nc_get_vars_ TYPE family of functions read a subsampled (strided) array section of values from a netCDF variable of an open netCDF dataset. The subsampled array section is specified by giving a corner, a vector of edge lengths, and a stride vector. The values are read with the last dimension of the netCDF variable varying fastest. The netCDF dataset must be in data mode. The functions for types ubyte, ushort, uint, longlong, ulonglong, and string are only available for netCDF-4/HDF5 files. The nc_get_vars() function will read a variable of any type, including user defined type. For this function, the type of the data in memory must match the type of the variable - no data conversion is done. Usage ===== int nc_get_vars_text (int ncid, int varid, const size_t start[], const size_t count[], const ptrdiff_t stride[], char *tp); int nc_get_vars_uchar (int ncid, int varid, const size_t start[], const size_t count[], const ptrdiff_t stride[], unsigned char *up); int nc_get_vars_schar (int ncid, int varid, const size_t start[], const size_t count[], const ptrdiff_t stride[], signed char *cp); int nc_get_vars_short (int ncid, int varid, const size_t start[], const size_t count[], const ptrdiff_t stride[], short *sp); int nc_get_vars_int (int ncid, int varid, const size_t start[], const size_t count[], const ptrdiff_t stride[], int *ip); int nc_get_vars_long (int ncid, int varid, const size_t start[], const size_t count[], const ptrdiff_t stride[], long *lp); int nc_get_vars_float (int ncid, int varid, const size_t start[], const size_t count[], const ptrdiff_t stride[], float *fp); int nc_get_vars_double(int ncid, int varid, const size_t start[], const size_t count[], const ptrdiff_t stride[], double *dp) int nc_get_vars_ubyte (int ncid, int varid, const size_t *startp, const size_t *countp, const ptrdiff_t *stridep, unsigned char *ip); int nc_get_vars_ushort(int ncid, int varid, const size_t *startp, const size_t *countp, const ptrdiff_t *stridep, unsigned short *ip); int nc_get_vars_uint (int ncid, int varid, const size_t *startp, const size_t *countp, const ptrdiff_t *stridep, unsigned int *ip); int nc_get_vars_longlong (int ncid, int varid, const size_t *startp, const size_t *countp, const ptrdiff_t *stridep, long long *ip); int nc_get_vars_ulonglong(int ncid, int varid, const size_t *startp, const size_t *countp, const ptrdiff_t *stridep, unsigned long long *ip); int nc_get_vars_string(int ncid, int varid, const size_t *startp, const size_t *countp, const ptrdiff_t *stridep, char **ip); int nc_get_vars (int ncid, int varid, const size_t *startp, const size_t *countp, const ptrdiff_t *stridep, void *ip); `ncid' NetCDF ID, from a previous call to nc_open or nc_create. `varid' Variable ID. `start' A vector of size_t integers specifying the index in the variable where the first of the data values will be read. The indices are relative to 0, so for example, the first data value of a variable would have index (0, 0, ... , 0). The elements of start correspond, in order, to the variable's dimensions. Hence, if the variable is a record variable, the first index corresponds to the starting record number for reading the data values. `count' A vector of size_t integers specifying the number of indices selected along each dimension. To read a single value, for example, specify count as (1, 1, ... , 1). The elements of count correspond, in order, to the variable's dimensions. Hence, if the variable is a record variable, the first element of count corresponds to a count of the number of records to read. Note: setting any element of the count array to zero causes the function to exit without error, and without doing anything. `stride' A vector of ptrdiff_t integers specifying, for each dimension, the interval between selected indices. The elements of the stride vector correspond, in order, to the variable's dimensions. A value of 1 accesses adjacent values of the netCDF variable in the corresponding dimension; a value of 2 accesses every other value of the netCDF variable in the corresponding dimension; and so on. A NULL stride argument is treated as (1, 1, ... , 1). `tp' `up' `cp' `sp' `ip' `lp' `fp' `dp' Pointer to the location into which the data value is read. If the type of data value differs from the netCDF variable type, type conversion will occur. *Note Type Conversion: (netcdf)Type Conversion. Return Codes ============ * NC_NOERR No error. * NC_EHDFERR Error reported by HDF5 layer. * NC_ENOTVAR The variable ID is invalid for the specified netCDF dataset. * NC_EINVALCOORDS The specified corner indices were out of range for the rank of the specified variable. For example, a negative index, or an index that is larger than the corresponding dimension length will cause an error. * NC_EEDGE The specified edge lengths added to the specified corner would have referenced data out of range for the rank of the specified variable. For example, an edge length that is larger than the corresponding dimension length minus the corner index will cause an error. * NC_ERANGE One or more of the specified values are out of the range of values representable by the external data type of the variable. (Does not apply to the nc_get_vars() function). * NC_EINDEFINE The specified netCDF is in define mode rather than data mode. * NC_EBADID The specified netCDF ID does not refer to an open netCDF dataset. * NC_ECHAR Attempt to convert to or from char. * NC_ENOMEM Out of memory. Example ======= Here is an example that uses nc_get_vars_double to read every other value in each dimension of the variable named rh from an existing netCDF dataset named foo.nc. For simplicity in this example, we assume that we know that rh is dimensioned with time, lat, and lon, and that there are three time values, five lat values, and ten lon values. #include ... #define TIMES 3 #define LATS 5 #define LONS 10 int status; /* error status */ int ncid; /* netCDF ID */ int rh_id; /* variable ID */ static size_t start[] = {0, 0, 0}; /* start at first value */ static size_t count[] = {TIMES, LATS, LONS}; static ptrdiff_t stride[] = {2, 2, 2};/* every other value */ double data[TIMES][LATS][LONS]; /* array to hold values */ ... status = nc_open("foo.nc", NC_NOWRITE, &ncid); if (status != NC_NOERR) handle_error(status); ... status = nc_inq_varid (ncid, "rh", &rh_id); if (status != NC_NOERR) handle_error(status); ... /* read subsampled values from netCDF variable into array */ status = nc_get_vars_double(ncid, rh_id, start, count, stride, &data[0][0][0]); if (status != NC_NOERR) handle_error(status); ...