Re: [Haskell-cafe] c2hs, size_t, and CSize -- argh!

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 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