| <html> |
| <head> |
| <title>SWIG:Examples:go:pointer</title> |
| </head> |
| |
| <body bgcolor="#ffffff"> |
| |
| <tt>SWIG/Examples/go/pointer/</tt> |
| <hr> |
| |
| <H2>Simple Pointer Handling</H2> |
| |
| <p> |
| This example illustrates a couple of techniques for handling simple |
| pointers in SWIG. The prototypical example is a C function that |
| operates on pointers such as this: |
| |
| <blockquote> |
| <pre> |
| void add(int *x, int *y, int *r) { |
| *r = *x + *y; |
| } |
| </pre> |
| </blockquote> |
| |
| By default, SWIG wraps this function exactly as specified and creates |
| an interface that expects pointer objects for arguments. This only |
| works when there is a precise correspondence between the C type and |
| some Go type. |
| <p> |
| |
| <h2>Other approaches</h2> |
| |
| <p> |
| <li>The SWIG pointer library provides a different, safer, way to |
| handle pointers. For example, in the interface file you would do |
| this: |
| |
| <blockquote> |
| <pre> |
| %include cpointer.i |
| %pointer_functions(int, intp); |
| </pre> |
| </blockquote> |
| |
| and from Go you would use pointers like this: |
| |
| <blockquote> |
| <pre> |
| a := example.New_intp() |
| b := example.New_intp() |
| c := example.New_intp() |
| Intp_Assign(a, 37) |
| Intp_Assign(b, 42) |
| |
| fmt.Println(" a =", a) |
| fmt.Println(" b =", b) |
| fmt.Println(" c =", c) |
| |
| // Call the add() function with some pointers |
| example.Add(a,b,c) |
| |
| // Now get the result |
| res := example.Intp_value(c) |
| fmt.Println(" 37 + 42 =", res) |
| |
| // Clean up the pointers |
| example.Delete_intp(a) |
| example.Delete_intp(b) |
| example.Delete_intp(c) |
| </pre> |
| </blockquote> |
| |
| <p> |
| <li>Use the SWIG typemap library. This library allows you to |
| completely change the way arguments are processed by SWIG. For |
| example: |
| |
| <blockquote> |
| <pre> |
| %include "typemaps.i" |
| void add(int *INPUT, int *INPUT, int *OUTPUT); |
| </pre> |
| </blockquote> |
| |
| And in a Go program: |
| |
| <blockquote> |
| <pre> |
| r := []int{0} |
| example.Sub(37,42,r) |
| fmt.Println("Result =", r[0]) |
| </pre> |
| </blockquote> |
| Needless to say, this is substantially easier although a bit unusual. |
| |
| <p> |
| <li>A final alternative is to use the typemaps library in combination |
| with the %apply directive. This allows you to change the names of parameters |
| that behave as input or output parameters. For example: |
| |
| <blockquote> |
| <pre> |
| %include "typemaps.i" |
| %apply int *INPUT {int *x, int *y}; |
| %apply int *OUTPUT {int *r}; |
| |
| void add(int *x, int *y, int *r); |
| void sub(int *x, int *y, int *r); |
| void mul(int *x, int *y, int *r); |
| ... etc ... |
| </pre> |
| </blockquote> |
| |
| </ul> |
| |
| <h2>Example</h2> |
| |
| The following example illustrates the use of these features for pointer |
| extraction. |
| |
| <ul> |
| <li> <a href="example.c">example.c</a> (C Source) |
| <li> <a href="example.i">example.i</a> (SWIG interface) |
| <li> <a href="runme.go">runme.go</a> (Go program) |
| </ul> |
| |
| <h2>Notes</h2> |
| |
| <ul> |
| <li>Since pointers are used for so many different things (arrays, output values, |
| etc...) the complexity of pointer handling can be as complicated as you want to |
| make it. |
| |
| <p> |
| <li>More documentation on the typemaps.i and cpointer.i library files can be |
| found in the SWIG user manual. The files also contain documentation. |
| |
| </ul> |
| |
| <hr> |
| </body> |
| </html> |
