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.