Use Pyrex instead (Re: newbie at SWIG, help needed with typemaps)

[Greg Ewing (using news.cis.dfn.de)]

Josh wrote:
> I hope this is not OT in this group. If it is, do let me know and I'll try 
> my luck elsewhere.

Seems pretty much on-topic to me...

> I have a simple C function. When called from a C 
> program, void carr is handed a properly malloc'ed double pointer and an int 
> len. carr then proceeds to fill up the first len locations of the double 
> array represented by double *sd. When called from python, I just want to 
> pass the len as in (in module trl) trl.carr(len). In that case, the wrapped 
> C function should then proceed to dynamically allocate the double array, 
> fill it up, convert it to a Python object, and return a list of  len 
> elements.

Instead of SWIG, you might prefer to use Pyrex to wrap your C code:

    http://www.cosc.canterbury.ac.nz/~greg/python/Pyrex/

This is exactly the sort of problem I designed Pyrex to solve.
The Pyrex code for it would look something like this (warning,
untested):

   cdef extern void *malloc(int)
   cdef extern void free(void *)
   cdef extern void carr(double *, int)

   def pycarr(int n):
     cdef double *a
     cdef int i
     a = <double*>malloc(n * sizeof(double))
     carr(a, n)
     result = []
     for i from 0 <= i < n:
       result.append(a[i])
     free(a)
     return result

I hope you'll agree that this is a LOT saner than messing
about with SWIG!

(A minor problem is that you can't currently call the
Python function "carr" or it will conflict with the
C one. That will be fixed in a later release...)

-- 
Greg Ewing, Computer Science Dept,
University of Canterbury,	
Christchurch, New Zealand
http://www.cosc.canterbury.ac.nz/~greg