Hi Duncan,

Yes, I forgot to leave out that I'd like to see 'size_t' mapped to CSize.

As a (dirty) workaround, one can use 'castPtr' as the marshaler when dealing with pointers to 'size_t'. I'm a little more concerned about FunPtr's (though 'castPtr' still makes the issue go away).

Here's my specific case dealing with function pointers:

In 64bit world, it looks like this:
type ReadableCallback = Ptr () -> Ptr CUChar -> Ptr CULong -> IO CUInt
{#fun gcry_ac_io_init_readable_callback {
        id `ACIO',
        id `FunPtr ReadableCallback',
        id `Ptr ()'
    } -> `()'#}

In 32bit world, it looks like this:
type ReadableCallback = Ptr () -> Ptr CUChar -> Ptr CUInt -> IO CUInt
{#fun gcry_ac_io_init_readable_callback {
        id `ACIO',
        id `FunPtr ReadableCallback',
        id `Ptr ()'
    } -> `()'#}

I'd really like it if I could use 'Ptr CSize' (which corresponds to the 'size_t * ptr' in the C code).

My current workaround (which doesn't use a cast in Haskell) is to redefine the function pointer type in a C header file to use 'unsigned long' instead of 'size_t', but this gets cludgy in a hurry. If c2hs could translate to CSize directly, I could pass a pointer to CSize.

Is it really such a problem to make the conversion? My assumption is that CSize would match 'size_t' for the specific architecture.

Thanks for your comment.

/jve


On Thu, Oct 1, 2009 at 12:37 PM, Duncan Coutts <duncan.coutts@googlemail.com> wrote:
On Thu, 2009-10-01 at 10:20 -0400, John Van Enk wrote:
> Hello List,
>
> I'm running into a problem with c2hs and how it parses the C typedef
> 'size_t'. On 32bit systems, this ends up being parsed as a CUInt. On
> 64bit systems, this ends up as a CULong. This gets especially sticky
> with function pointers.

Right. Of course that's because on those different platforms size_t
really is a typedef for unsigned int or unsigned long.

> I see there is a ticket open for this:
> http://hackage.haskell.org/trac/c2hs/ticket/20
>
> Has any one else run into this issue? Is there a good workaround that
> doesn't involve writing a C function/typedef for each collision?

So what you would want, presumably, is to map the "size_t" typedef to
the Haskell type Foreign.C.Types.CSize, rather than what c2hs discovers
as the actual raw type of "size_t". Then you're making the promise that
unsigned long, or unsigned int really really does match
Foreign.C.Types.CSize.

Currently c2hs has no support for remapping basic types like that.

As for a workaround, just use fromIntegral to convert to CSize. You know
this is always possible because you know CSize matches CUInt or CULong
on the appropriate platforms.

$ cat foo.h
#include <stddef.h>
size_t foo(void);

$ cat foo.c
#include "foo.h"
size_t foo(void) { return 42; }

$ cat foo.chs

import Foreign.C.Types
foo :: IO CSize
foo = fmap fromIntegral {# call foo as bar #}

$ gcc -c foo.c
$ c2hs foo.h foo.chs
$ ghci foo.hs -fffi foo.o
Main> foo
42


Duncan