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git-svn-id: https://swig.svn.sourceforge.net/svnroot/swig/trunk/SWIG@841 626c5289-ae23-0410-ae9c-e8d60b6d4f22
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Dave Beazley 2000-09-04 15:30:21 +00:00
commit 92093ca12d
6 changed files with 134 additions and 13 deletions
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7
Examples/python/funcptr/example.h Normal file
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/* file: example.h */
extern int do_op(int,int, int (*op)(int,int));
extern int add(int,int);
extern int sub(int,int);
extern int mul(int,int);

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Examples/python/funcptr/example.i Normal file
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/* File : example.i */
%module example
%{
#include "example.h"
%}
/* Wrap a function taking a pointer to a function */
extern int do_op(int a, int b, int (*op)(int, int));
/* Now install a bunch of "ops" as constants */
%constant(int (*)(int,int)) ADD = add;
%constant(int (*)(int,int)) SUB = sub;
%constant(int (*)(int,int)) MUL = mul;

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Examples/python/funcptr/example.py Normal file
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# file: example.py
import example
a = 37
b = 42
# Now call our C function with a bunch of callbacks
print "Trying some C callback functions"
print " a =", a
print " b =", b
print " ADD(a,b) =", example.do_op(a,b,example.ADD)
print " SUB(a,b) =", example.do_op(a,b,example.SUB)
print " MUL(a,b) =", example.do_op(a,b,example.MUL)
print "Here is what the C callback function objects look like in Python"
print " ADD =", example.ADD
print " SUB =", example.SUB
print " MUL =", example.MUL

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Examples/python/funcptr/index.html Normal file
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<html>
<head>
<title>SWIG:Examples:python:funcptr</title>
</head>
<body bgcolor="#ffffff">
<tt>SWIG/Examples/python/funcptr/</tt>
<hr>
<H2>Pointers to Functions</H2>
<tt>$Header$</tt><br>
<p>
Okay, just what in the heck does SWIG do with a declaration like this?
<blockquote>
<pre>
int do_op(int a, int b, int (*op)(int, int));
</pre>
</blockquote>
Well, it creates a wrapper as usual. Of course, that does raise some
questions about the third argument (the pointer to a function).
<p>
In this case, SWIG will wrap the function pointer as it does for all other
pointers. However, in order to actually call this function from a script,
you will need to pass some kind of C function pointer object. In C,
this is easy, you just supply a function name as an argument like this:
<blockquote>
<pre>
/* Some callback function */
int add(int a, int b) {
return a+b;
}
...
int r = do_op(x,y,add);
</pre>
</blockquote>
To make this work with SWIG, you will need to do a little extra work. Specifically,
you need to create some function pointer objects using the %constant directive like this:
<blockquote>
<pre>
%constant(int (*)(int,int)) ADD = add;
</pre>
</blockquote>
Now, in a script, you would do this:
<blockquote>
<pre>
r = do_op(x,y, ADD)
</pre>
</blockquote>
<h2>An Example</h2>
Here are some files that illustrate this with a simple example:
<ul>
<li><a href="example.c">example.c</a>
<li><a href="example.h">example.h</a>
<li><a href="example.i">example.i</a> (SWIG interface)
<li><a href="example.py">example.py</a> (Sample script)
</ul>
<h2>Notes</h2>
<ul>
<li>The value of a function pointer must correspond to a function written in C or C++.
It is not possible to pass an arbitrary Python function object in as a substitute for a C
function pointer.
<p>
<li>A python function can be used as a C/C++ callback if you write some
clever typemaps and are very careful about how you create your extension.
This is an advanced topic not covered here.
</ul>
<hr>
</body>
</html>