Re: [Swig-user] Accessing C int array in Python

[Nitro <ni...@dr...>]

Am 26.03.2008, 20:49 Uhr, schrieb Donovan Parks <don...@gm...>:

> Hello,
>
> I have a simple C++ function that I am wrapping with swig:
>
> void getImage(int frameNum, int* imageData);
>
> I have successfully wrapped this function. Using a simple helper
> function, I can create a C int array in python and pass it into this
> function. Now, I would like to be able to access the elements of this
> C int array in python. Clearly I could write a simple C helper
> function that took in the array points and the desired element and
> would return the value of the array at the element. Is there a way to
> access the elements of this C array directly? Can I convert the C

Yes. Instead of using a helper function you can also use a typemap. Here  
http://www.swig.org/Doc1.3/Typemaps.html#Typemaps_nn39 is some more  
information. Specifically the "out" typemap is interesting here:

%typemap(out) float [ANY] {
   int i;
   $result = PyList_New($1_dim0);
   for (i = 0; i < $1_dim0; i++) {
     PyObject *o = PyFloat_FromDouble((double) $1[i]);
     PyList_SetItem($result,i,o);
   }
}

You can translate this to something like

typemap(out) int* {
   int i;
   int length = XXX;
   $result = PyList_New( length );
   for (i = 0; i < length; i++) {
     PyObject *o = PyInt_FromLong( $1[i] );
     PyList_SetItem($result,i,o);
   }
}

Note that XXX is undefined. It really depends on the size of your array.  
Maybe you are passing a fixed size array or it is zero-terminated. This is  
something you need to fill in yourself.

-Matthias