SWIG:Examples:go:variables

SWIG/Examples/go/variables/

Wrapping C Global Variables

When a C global variable appears in an interface file, SWIG provides getter and setter functions for the variable. The getter function is named Get followed by the capitalized name of the variable. The setter variable starts with Set instead. The getter function takes no parameters and returns the value of the variable. The setter function takes a single parameter with the same type as the variable, and returns nothing.

Click here to see a SWIG interface with some variable declarations in it.

Manipulating Variables from Go

For example, if the package is called example, the global variable

double foo;

will be accessed from Go as

example.GetFoo();
example.SetFoo(12.3);

Click here to see the example program that updates and prints out the values of the variables using this technique.

Key points

The name of the variable is capitalized.
When a global variable has the type "char *", SWIG manages it as a character string.
signed char and unsigned char are handled as small 8-bit integers.
String array variables such as 'char name[256]' are managed as Go strings, but when setting the value, the result is truncated to the maximum length of the array. Furthermore, the string is assumed to be null-terminated.
When structures and classes are used as global variables, they are mapped into pointers. Getting the "value" returns a pointer to the global variable. Setting the value of a structure results in a memory copy from a pointer to the global.

Creating read-only variables

The %immutable and %mutable directives can be used to specify a collection of read-only variables. A read only variable will have a getter function but no setter function. For example:

%immutable;
int    status;
double blah;
...
%mutable;

The %immutable directive remains in effect until it is explicitly disabled using the %mutable directive.