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git-svn-id: https://swig.svn.sourceforge.net/svnroot/swig/trunk@12108 626c5289-ae23-0410-ae9c-e8d60b6d4f22
87 lines
2.3 KiB
HTML
87 lines
2.3 KiB
HTML
<html>
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<head>
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<title>SWIG:Examples:go:variables</title>
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</head>
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<body bgcolor="#ffffff">
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<tt>SWIG/Examples/go/variables/</tt>
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<hr>
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<H2>Wrapping C Global Variables</H2>
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<p>
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When a C global variable appears in an interface file, SWIG provides
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getter and setter functions for the variable. The getter function is
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named <tt>Get</tt> followed by the capitalized name of the variable.
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The setter variable starts with <tt>Set</tt> instead. The getter
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function takes no parameters and returns the value of the variable.
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The setter function takes a single parameter with the same type as the
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variable, and returns nothing.
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<p>Click <a href="example.i">here</a> to see a SWIG interface with
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some variable declarations in it.
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<h2>Manipulating Variables from Go</h2>
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For example, if the package is called <tt>example</tt>, the global
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variable
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<blockquote>
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<pre>
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double foo;
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</pre>
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</blockquote>
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will be accessed from Go as
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<blockquote>
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<pre>
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example.GetFoo();
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example.SetFoo(12.3);
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</pre>
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</blockquote>
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Click <a href="runme.go">here</a> to see the example program that
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updates and prints out the values of the variables using this
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technique.
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<h2>Key points</h2>
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<ul>
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<li>The name of the variable is capitalized.
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<li>When a global variable has the type "<tt>char *</tt>", SWIG
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manages it as a character string.
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<li><tt>signed char</tt> and <tt>unsigned char</tt> are handled as
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small 8-bit integers.
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<li>String array variables such as '<tt>char name[256]</tt>' are
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managed as Go strings, but when setting the value, the result is
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truncated to the maximum length of the array. Furthermore, the string
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is assumed to be null-terminated.
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<li>When structures and classes are used as global variables, they are
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mapped into pointers. Getting the "value" returns a pointer to the
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global variable. Setting the value of a structure results in a memory
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copy from a pointer to the global.
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</ul>
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<h2>Creating read-only variables</h2>
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The <tt>%immutable</tt> and <tt>%mutable</tt> directives can be used
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to specify a collection of read-only variables. A read only variable
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will have a getter function but no setter function. For example:
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<blockquote>
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<pre>
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%immutable;
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int status;
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double blah;
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...
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%mutable;
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</pre>
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</blockquote>
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The <tt>%immutable</tt> directive remains in effect until it is
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explicitly disabled using the <tt>%mutable</tt> directive.
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</body>
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</html>
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<hr>
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