Re: [Swig-user] Accessing abstract/opaque C stuctures from python

[David B. <dav...@da...>]

What about just replacing foo_init with a helper function?

%inline %{
Foo *create_Foo() {
     Foo *f = 0;
     foo_init(&f);
     return f;
}
%}

Then, use this to create a Foo * object.

-- Dave


On Jan 14, 2008, at 12:46 AM, Bob Hepple wrote:

> I dug through the doco and maillist archive for a few hours but I'm  
> still stuck. It seems to me that this should be a fairly simple  
> thing to do, but ...
>
> I have a function in a shared library libfoo.so defined with foo.h:
>
> foo.h:
> typedef struct foo_st FOO;
> int foo_init(FOO **foo); /* malloc memory for structure */
> int foo_use(FOO *foo); /* do something with the structure */
> int foo_fini(FOO *foo); /* free up the structure */
>
> ... that I would normally call from C like this:
> FOO *foo = NULL;
> int status = 0;
> status = foo_init(&foo);
> ...
> foo_use(foo); /* etc */
> foo_fini(foo);
>
> ... ie a fairly typical abstract opaque data structure
>
>
> When I swig this with the following simple foo.i file:
>
> %module foo
> %{
> #include "foo.h"
> %}
> %include "foo.h"
>
> ... I get python errors:
>
> import foo
> foo.foo_init ()
> =>
>       foo.foo_init()
> TypeError: foo_init() takes exactly 1 argument (0 given)
> .. which is understandable, but how do I give it an abstract  
> pointer? This also fails:
>
> import foo
> my_foo = foo.FOO ()
> foo.foo_init(my_foo)
> =>
>        my_foo = foo.FOO()
> AttributeError: 'module' object has no attribute 'FOO'
>
> I _had _thought that I could %typemap the need for an argument out  
> of it with this (scoured from the doco):
>
> %module foo
> %include "typemaps.i"
> %typemap(argout) FOO **foo {
>     PyObject *o, *o2, *o3;
>     o = PyLong_FromVoidPtr(*$1);
>     if ((!$result) || ($result == Py_None)) {
>         $result = o;
>     } else {
>         if (!PyTuple_Check($result)) {
>             PyObject *o2 = $result;
>             $result = PyTuple_New(1);
>             PyTuple_SetItem($result,0,o2);
>         }
>         o3 = PyTuple_New(1);
>         PyTuple_SetItem(o3,0,o);
>         o2 = $result;
>         $result = PySequence_Concat(o2,o3);
>         Py_DECREF(o2);
>         Py_DECREF(o3);
>     }
> }
> %{
> #include "foo.h"
> %}
> %include " foo.h"
>
> ... but it gives exactly the same errors.
>
> Any ideas out there?
>
> For completeness, here's the build chain that I used:
>
> cc -c foo.c
> ld -shared -o libfoo.so foo.o
> swig -python foo.i
> cc -c foo_wrap.c -I /usr/include/python2.5
> ld -shared -rpath "`pwd`" -o _foo.so foo_wrap.o libfoo.so
>
> And the source code foo.c:
>
> struct foo_st {
>     int i;
>     int b;
> };
>
> #include "foo.h"
> #include "malloc.h"
> #define FOO_SIZE 10
>
> int foo_init(FOO **foo)
> {
>     *foo = malloc(FOO_SIZE);
>     return(0);
> }
>
> int foo_use(FOO *foo)
> {
>     foo->i = 1;
>     return(0);
> }
>
> int foo_fini(FOO *foo)
> {
>     free(foo);
>     return(0);
> }
>
>
>
>
>
>
>
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