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<title>SWIG:Examples:tcl:simple</title>
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<tt>SWIG/Examples/tcl/simple/</tt>
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<H2>Simple Tcl Example</H2>
<tt>$Header: /cvs/projects/SWIG/Examples/tcl/simple/index.html,v 1.1 2000/06/17 21:41:01 beazley Exp $</tt><br>
<p>
This example illustrates how you can hook Tcl to a very simple C program containing
a function and a global variable.
<h2>The C Code</h2>
Suppose you have the following C code:
<blockquote>
<pre>
/* File : example.c */
/* A global variable */
double Foo = 3.0;
/* Compute the greatest common divisor of positive integers */
int gcd(int x, int y) {
int g;
g = y;
while (x > 0) {
g = x;
x = y % x;
y = g;
}
return g;
}
</pre>
</blockquote>
<h2>The SWIG interface</h2>
Here is a simple SWIG interface file:
<blockquote>
<pre>
/* File: example.i */
%module example
extern int gcd(int x, int y);
extern double Foo;
</pre>
</blockquote>
<h2>Compilation</h2>
<ol>
<li><tt>swig -tcl <a href="example.i">example.i</a></tt>
<p>
<li>Compile <tt><a href="example_wrap.c">example_wrap.c</a></tt> and <tt><a href="example.c">example.c</a></tt>
to create the extension <tt>example.so</tt>.
</ol>
<h2>Using the extension</h2>
Click <a href="example.tcl">here</a> to see a script that calls our C functions from Tcl.
<h2>Key points</h2>
<ul>
<li>Use the <tt>load</tt> statement to load your extension module into Tcl. For example:
<blockquote>
<pre>
load ./example.so
</pre>
</blockquote>
<li>C functions work just like Tcl functions. For example:
<blockquote>
<pre>
set g [gcd 42 105]
</pre>
</blockquote>
<li>C global variables are accessed as Tcl variables. For example:
<blockquote>
<pre>
set a $Foo
set Foo $newvalue
</pre>
</blockquote>
</ul>
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