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

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

It's probably much easier to get the status if you organize the  
function like this:

Foo *create_Foo(int *status) {
      Foo *f = 0;
      *status = foo_init(&f);
      return f;
}

You can then apply one of the existing OUTPUT typemaps to the status  
parameter.

-- Dave




On Jan 14, 2008, at 5:36 PM, Bob Hepple wrote:

> Thanks, David, that works _but_ I also need to get the status out  
> of it - that's why I was hoping to be able to use the "pointer to  
> the handle" approach.
> I'll have a go at trying to get create_Foo() return both  
> parameters, and post my results here.
>
> BTW if I get this polished up, is there a good place to post it in  
> the doco as a worked example (apart from here, that is) ? I'm sure  
> it'd be useful to others.
>
> Cheers
>
>
> Bob
>
>
> On Jan 14, 2008 6:38 PM, David Beazley <dav...@da...> wrote:
> 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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