trunk/Examples/perl5/variables/index.html - third_party/swig - Git at Google

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 <title>SWIG:Examples:perl5:variables</title>
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 <tt>SWIG/Examples/perl5/variables/</tt>
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 <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>

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	<title>SWIG:Examples:perl5:variables</title>
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	<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>

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