new example
git-svn-id: https://swig.svn.sourceforge.net/svnroot/swig/trunk/SWIG@809 626c5289-ae23-0410-ae9c-e8d60b6d4f22
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Dave Beazley
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6 changed files with 273 additions and 0 deletions
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@ -20,6 +20,7 @@ certain C declarations are turned into constants.
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<li><a href="value/index.html">value</a>. How to pass and return structures by value.
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<li><a href="class/index.html">class</a>. Wrapping a simple C++ class.
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<li><a href="reference/index.html">reference</a>. C++ references.
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<li><a href="pointer/index.html">pointer</a>. Simple pointer handling.
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</ul>
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<h2>Compilation Issues</h2>
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18
Examples/python/pointer/Makefile
Normal file
18
Examples/python/pointer/Makefile
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@ -0,0 +1,18 @@
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TOP = ../..
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SWIG = $(TOP)/../swig
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SRCS = example.c
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TARGET = example
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INTERFACE = example.i
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all::
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$(MAKE) -f $(TOP)/Makefile SRCS='$(SRCS)' SWIG='$(SWIG)' \
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TARGET='$(TARGET)' INTERFACE='$(INTERFACE)' python
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static::
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$(MAKE) -f $(TOP)/Makefile SRCS='$(SRCS)' SWIG='$(SWIG)' \
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TARGET='mypython' INTERFACE='$(INTERFACE)' python_static
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clean::
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rm -f *_wrap* *.o *~ *.so mypython *.pyc .~* core
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check: all
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16
Examples/python/pointer/example.c
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16
Examples/python/pointer/example.c
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@ -0,0 +1,16 @@
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/* File : example.c */
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void add(int *x, int *y, int *result) {
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*result = *x + *y;
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}
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void sub(int *x, int *y, int *result) {
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*result = *x - *y;
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}
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int divide(int n, int d, int *r) {
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int q;
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q = n/d;
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*r = n - q*d;
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return q;
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}
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23
Examples/python/pointer/example.i
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23
Examples/python/pointer/example.i
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@ -0,0 +1,23 @@
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/* File : example.i */
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%module example
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/* This example illustrates a couple of different techniques
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for manipulating C pointers */
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/* First we'll use the pointer library */
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extern void add(int *x, int *y, int *result);
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%include pointer.i
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/* Next we'll use some typemaps */
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%include typemaps.i
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extern void sub(int *INPUT, int *INPUT, int *OUTPUT);
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/* Next we'll use typemaps and the %apply directive */
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%apply int *OUTPUT { int *r };
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extern int divide(int n, int d, int *r);
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42
Examples/python/pointer/example.py
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42
Examples/python/pointer/example.py
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@ -0,0 +1,42 @@
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# file: example.py
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import example;
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# First create some objects using the pointer library.
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print "Testing the pointer library";
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a = example.ptrcreate("int",37);
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b = example.ptrcreate("int",42);
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c = example.ptrcreate("int");
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print " a =",a
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print " b =",b
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print " c =",c
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# Call the add() function with some pointers
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example.add(a,b,c)
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# Now get the result
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r = example.ptrvalue(c)
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print " 37 + 42 =",r
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# Clean up the pointers
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example.ptrfree(a)
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example.ptrfree(b)
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example.ptrfree(c)
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# Now try the typemap library
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# This should be much easier. Now how it is no longer
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# necessary to manufacture pointers.
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print "Trying the typemap library";
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r = example.sub(37,42)
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print " 37 - 42 =",r
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# Now try the version with multiple return values
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print "Testing multiple return values";
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q,r = example.divide(42,37)
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print " 42/37 = %d remainder %d" % (q,r)
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173
Examples/python/pointer/index.html
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173
Examples/python/pointer/index.html
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@ -0,0 +1,173 @@
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<html>
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<head>
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<title>SWIG:Examples:python:pointer</title>
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</head>
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<body bgcolor="#ffffff">
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<tt>SWIG/Examples/python/pointer/</tt>
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<hr>
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<H2>Simple Pointer Handling</H2>
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<tt>$Header$</tt><br>
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<p>
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This example illustrates a couple of techniques for handling
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simple pointers in SWIG. The prototypical example is a C function
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that operates on pointers such as this:
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<blockquote>
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<pre>
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void add(int *x, int *y, int *r) {
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*r = *x + *y;
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}
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</pre>
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</blockquote>
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By default, SWIG wraps this function exactly as specified and creates
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an interface that expects pointer objects for arguments. The only
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problem is how does one go about creating these objects from a script?
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<h2>Possible Solutions</h2>
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<ul>
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<li>Write some helper functions to explicitly create objects. For
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example:
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<blockquote>
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<pre>
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int *new_int(int ivalue) {
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int *i = (int *) malloc(sizeof(ivalue));
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*i = ivalue;
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return i;
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}
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int get_int(int *i) {
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return *i;
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}
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void delete_int(int *i) {
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free(i);
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}
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</pre>
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</blockquote>
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Now, in a script you would do this:
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<blockquote>
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<pre>
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a = new_int(37)
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b = new_int(42)
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c = new_int(0)
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add(a,b,c)
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r = get_int(c);
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print "Result =",r
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delete_int(a)
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delete_int(b)
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delete_int(c)
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</pre>
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</blockquote>
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<p>
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<li>Use the SWIG pointer library. For example, in the interface file
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you would do this:
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<blockquote>
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<pre>
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%include "pointer.i"
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</pre>
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</blockquote?
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and in a script you would do this:
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<blockquote>
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<pre>
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a = ptrcreate("int",37)
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b = ptrcreate("int",42)
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c = ptrcreate("int")
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add(a,b,c)
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r = ptrvalue(c)
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print "Result =",r
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ptrfree(a)
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ptrfree(b)
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ptrfree(c)
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</pre>
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</blockquote>
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The advantage to using the pointer library is that it unifies some of the helper
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functions behind a common set of names. For example, the same set of functions work
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with int, double, float, and other fundamental types.
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<p>
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<li>Use the SWIG typemap library. This library allows you to completely
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change the way arguments are processed by SWIG. For example:
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<blockquote>
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<pre>
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%include "typemaps.i"
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void add(int *INPUT, int *INPUT, int *OUTPUT);
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</pre>
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</blockquote>
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And in a script:
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<blockquote>
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<pre>
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r = add(37,42)
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print "Result =",r
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</pre>
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</blockquote>
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Needless to say, this is substantially easier.
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<p>
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<li>A final alternative is to use the typemaps library in combination
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with the %apply directive. This allows you to change the names of parameters
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that behave as input or output parameters. For example:
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<blockquote>
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<pre>
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%include "typemaps.i"
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%apply int *INPUT {int *x, int *y};
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%apply int *OUTPUT {int *r};
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void add(int *x, int *y, int *r);
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void sub(int *x, int *y, int *r);
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void mul(int *x, int *y, int *r);
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... etc ...
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</pre>
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</blockquote>
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</ul>
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<h2>Example</h2>
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The following example illustrates the use of these features for pointer
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extraction.
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<ul>
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<li> <a href="example.c">example.c</a> (C Source)
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<li> <a href="example.i">example.i</a> (Swig interface)
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<li> <a href="example.py">example.py</a> (Python Script)
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</ul>
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<h2>Notes</h2>
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<ul>
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<li>Since pointers are used for so many different things (arrays, output values,
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etc...) the complexity of pointer handling can be as complicated as you want to
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make it.
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<p>
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<li>More documentation on the typemaps.i and pointer.i library files can be
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found in the SWIG user manual. The files also contain documentation.
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<p>
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<li>The pointer.i library is designed primarily for convenience. If you
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are concerned about performance, you probably want to use a different
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approach.
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</ul>
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<hr>
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</body>
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</html>
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