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+<html>
+<head>
+<title>SWIG:Examples:perl5:variables</title>
+</head>
+
+<body bgcolor="#ffffff">
+
+<tt>SWIG/Examples/perl5/variables/</tt>
+<hr>
+
+<H2>Wrapping C Global Variables</H2>
+
+<p>
+When a C global variable appears in an interface file, SWIG tries to
+wrap it using a technique known as "variable linking."  The idea is
+pretty simple---we try to create a Perl variable that magically
+retrieves or updates the value of the underlying C variable when it is
+accessed.  Click <a href="example.i">here</a> to see a SWIG interface with some variable
+declarations in it.
+
+<h2>Manipulating Variables from Perl</h2>
+
+Accessing a C global variable from Perl is easy---just reference it like a normal Perl variable.
+Click <a href="runme.pl">here</a> to see a script that updates and prints some global variables.
+
+<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.  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.
+
+
+<h2>Notes:</h2>
+
+<ul>
+<li>When a global variable has the type "<tt>char *</tt>", SWIG manages it as a character
+string.   However, whenever the value of such a variable is set from Perl, the old
+value is destroyed using <tt>free()</tt> or <tt>delete</tt> (the choice of which depends
+on whether or not SWIG was run with the -c++ option).
+<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 Perl 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.
+<li>Variables are linked using Perl's magic mechanism.  Take a look at the Advanced Perl Programming book to 
+find out more about this feature.
+</ul>
+
+</body>
+</html>
+<hr>