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| <head> |
| <title>SWIG:Examples:go:variables</title> |
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| |
| <tt>SWIG/Examples/go/variables/</tt> |
| <hr> |
| |
| <H2>Wrapping C Global Variables</H2> |
| |
| <p> |
| When a C global variable appears in an interface file, SWIG provides |
| getter and setter functions for the variable. The getter function is |
| named <tt>Get</tt> followed by the capitalized name of the variable. |
| The setter variable starts with <tt>Set</tt> 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. |
| |
| <p>Click <a href="example.i">here</a> to see a SWIG interface with |
| some variable declarations in it. |
| |
| <h2>Manipulating Variables from Go</h2> |
| |
| For example, if the package is called <tt>example</tt>, the global |
| variable |
| |
| <blockquote> |
| <pre> |
| double foo; |
| </pre> |
| </blockquote> |
| |
| will be accessed from Go as |
| <blockquote> |
| <pre> |
| example.GetFoo(); |
| example.SetFoo(12.3); |
| </pre> |
| </blockquote> |
| |
| Click <a href="runme.go">here</a> to see the example program that |
| updates and prints out the values of the variables using this |
| technique. |
| |
| <h2>Key points</h2> |
| |
| <ul> |
| <li>The name of the variable is capitalized. |
| <li>When a global variable has the type "<tt>char *</tt>", SWIG |
| manages it as a character string. |
| <li><tt>signed char</tt> and <tt>unsigned char</tt> are handled as |
| small 8-bit integers. |
| <li>String array variables such as '<tt>char name[256]</tt>' 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. |
| <li>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. |
| </ul> |
| |
| <h2>Creating read-only variables</h2> |
| |
| The <tt>%immutable</tt> and <tt>%mutable</tt> 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: |
| |
| <blockquote> |
| <pre> |
| %immutable; |
| int status; |
| double blah; |
| ... |
| %mutable; |
| </pre> |
| </blockquote> |
| |
| The <tt>%immutable</tt> directive remains in effect until it is |
| explicitly disabled using the <tt>%mutable</tt> directive. |
| |
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