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git-svn-id: https://swig.svn.sourceforge.net/svnroot/swig/trunk@12108 626c5289-ae23-0410-ae9c-e8d60b6d4f22
143 lines
2.9 KiB
HTML
143 lines
2.9 KiB
HTML
<html>
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<title>SWIG:Examples:go:pointer</title>
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</head>
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<body bgcolor="#ffffff">
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<tt>SWIG/Examples/go/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 simple
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pointers in SWIG. The prototypical example is a C function that
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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. This only
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works when there is a precise correspondence between the C type and
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some Go type.
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<p>
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<h2>Other approaches</h2>
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<p>
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<li>The SWIG pointer library provides a different, safer, way to
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handle pointers. For example, in the interface file you would do
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this:
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<blockquote>
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<pre>
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%include cpointer.i
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%pointer_functions(int, intp);
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</pre>
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</blockquote>
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and from Go you would use pointers like 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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Intp_Assign(a, 37)
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Intp_Assign(b, 42)
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fmt.Println(" a =", a)
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fmt.Println(" b =", b)
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fmt.Println(" 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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res := example.Intp_value(c)
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fmt.Println(" 37 + 42 =", res)
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// Clean up the pointers
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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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<p>
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<li>Use the SWIG typemap library. This library allows you to
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completely change the way arguments are processed by SWIG. For
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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 Go program:
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<blockquote>
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<pre>
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r := []int{0}
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example.Sub(37,42,r)
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fmt.Println("Result =", r[0])
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</pre>
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</blockquote>
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Needless to say, this is substantially easier although a bit unusual.
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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="runme.go">runme.go</a> (Go program)
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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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