168 lines
3.4 KiB
HTML
168 lines
3.4 KiB
HTML
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<html>
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<head>
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<title>SWIG:Examples:perl5:pointer</title>
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</head>
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<body bgcolor="#ffffff">
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<tt>SWIG/Examples/perl5/pointer/</tt>
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<hr>
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<H2>Simple Pointer Handling</H2>
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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 = $r\n";
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delete_int($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 "cpointer.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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$a = example::new_intp();
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$b = example::new_intp();
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$c = example::new_intp();
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example::intp_assign($a,37);
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example::intp_assign($b,42);
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example::add($a,$b,$c);
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$r = example::intp_value($c);
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print "Result = $r\n";
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example::delete_intp($a);
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example::delete_intp($b);
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example::delete_intp($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\n";
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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 subtract(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="runme.pl">runme.pl</a> (Perl 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 cpointer.i library files can be
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found in the SWIG user manual. The files also contain documentation.
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</ul>
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<hr>
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</body>
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</html>
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