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git-svn-id: https://swig.svn.sourceforge.net/svnroot/swig/trunk@10005 626c5289-ae23-0410-ae9c-e8d60b6d4f22
63 lines
2.2 KiB
HTML
63 lines
2.2 KiB
HTML
<html>
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<head>
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<title>SWIG:Examples:perl5:variables</title>
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</head>
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<body bgcolor="#ffffff">
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<tt>SWIG/Examples/perl5/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 tries to
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wrap it using a technique known as "variable linking." The idea is
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pretty simple---we try to create a Perl variable that magically
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retrieves or updates the value of the underlying C variable when it is
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accessed. Click <a href="example.i">here</a> to see a SWIG interface with some variable
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declarations in it.
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<h2>Manipulating Variables from Perl</h2>
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Accessing a C global variable from Perl is easy---just reference it like a normal Perl variable.
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Click <a href="runme.pl">here</a> to see a script that updates and prints some global variables.
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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 to
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specify a collection of read-only variables. 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 explicitly disabled
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using the <tt>%mutable</tt> directive.
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<h2>Notes:</h2>
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<ul>
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<li>When a global variable has the type "<tt>char *</tt>", SWIG manages it as a character
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string. However, whenever the value of such a variable is set from Perl, the old
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value is destroyed using <tt>free()</tt> or <tt>delete</tt> (the choice of which depends
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on whether or not SWIG was run with the -c++ option).
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<li><tt>signed char</tt> and <tt>unsigned char</tt> are handled as small 8-bit integers.
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<li>String array variables such as '<tt>char name[256]</tt>' are managed as Perl strings, but
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when setting the value, the result is truncated to the maximum length of the array. Furthermore, the string is assumed to be null-terminated.
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<li>When structures and classes are used as global variables, they are mapped into pointers.
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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.
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<li>Variables are linked using Perl's magic mechanism. Take a look at the Advanced Perl Programming book to
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find out more about this feature.
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</ul>
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</body>
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</html>
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<hr>
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