PageRenderTime 11ms CodeModel.GetById 8ms app.highlight 1ms RepoModel.GetById 0ms app.codeStats 0ms

/tags/rel-1-3-25/SWIG/Examples/perl5/variables/index.html

#
HTML | 65 lines | 50 code | 15 blank | 0 comment | 0 complexity | 41b5653827514565f443cc719105f48e MD5 | raw file
Possible License(s): LGPL-2.1, Cube, GPL-3.0, 0BSD, GPL-2.0
 1<html>
 2<head>
 3<title>SWIG:Examples:perl5:variables</title>
 4</head>
 5
 6<body bgcolor="#ffffff">
 7
 8<tt>SWIG/Examples/perl5/variables/</tt>
 9<hr>
10
11<H2>Wrapping C Global Variables</H2>
12
13<tt>$Header$</tt><br>
14
15<p>
16When a C global variable appears in an interface file, SWIG tries to
17wrap it using a technique known as "variable linking."  The idea is
18pretty simple---we try to create a Perl variable that magically
19retrieves or updates the value of the underlying C variable when it is
20accessed.  Click <a href="example.i">here</a> to see a SWIG interface with some variable
21declarations in it.
22
23<h2>Manipulating Variables from Perl</h2>
24
25Accessing a C global variable from Perl is easy---just reference it like a normal Perl variable.
26Click <a href="runme.pl">here</a> to see a script that updates and prints some global variables.
27
28<h2>Creating read-only variables</h2>
29
30The <tt>%immutable</tt> and <tt>%mutable</tt> directives can be used to
31specify a collection of read-only variables.  For example:
32
33<blockquote>
34<pre>
35%immutable;
36int    status;
37double blah;
38...
39%mutable;
40</pre>
41</blockquote>
42
43The <tt>%immutable</tt> directive remains in effect until it is explicitly disabled
44using the <tt>%mutable</tt> directive.
45
46
47<h2>Notes:</h2>
48
49<ul>
50<li>When a global variable has the type "<tt>char *</tt>", SWIG manages it as a character
51string.   However, whenever the value of such a variable is set from Perl, the old
52value is destroyed using <tt>free()</tt> or <tt>delete</tt> (the choice of which depends
53on whether or not SWIG was run with the -c++ option).
54<li><tt>signed char</tt> and <tt>unsigned char</tt> are handled as small 8-bit integers.
55<li>String array variables such as '<tt>char name[256]</tt>' are managed as Perl strings, but
56when setting the value, the result is truncated to the maximum length of the array.  Furthermore, the string is assumed to be null-terminated.
57<li>When structures and classes are used as global variables, they are mapped into pointers.
58Getting 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.
59<li>Variables are linked using Perl's magic mechanism.  Take a look at the Advanced Perl Programming book to 
60find out more about this feature.
61</ul>
62
63</body>
64</html>
65<hr>