On Tue, 2006-01-17 at 13:42 -0600, Green Bryan - bgreen wrote:
Does anyone know of libtiff having been wrapped for Haskell? If not, where could I find a good tutorial on wrapping a c library with functions that have variable argument parameters?
The Haskell FFI does not support calling "varargs" C functions. You could write some C wrapper code that exposes just ordinary fixed arg functions and call the vararg ones in the C wrapper. How that wrapper code will work depends on just how 'variable' the varargs functions you're wrapping are. If you can make do with just a fixed number of variants then fine. If there is no upper bound on the number of args then you're in a difficult position. There is no portable way of constructing a va_list type. In your case I guess you're trying to bind: int TIFFSetField(TIFF *tif, ttag_t tag, ...) int TIFFGetField(TIFF *tif, ttag_t tag, ...) Fortunately there are a limited number of tags, albeit rather a lot of them. I'd suggest the best you can do is to write a C function that takes a pointer to a C union of all the different possible tags. Then your C function will switch on the tag, extract the values from the union and call TIFFSetField/TIFFGetField appropriately. For example: union tfield { struct tfield_ARTIST { char** field1; }; struct tfield_BADFAXLINES { uint32** field1; }; /* etc for all 100ish tags */ }; /* our wrapper function */ int wrapper_TIFFSetField(TIFF *tif, ttag_t tag, tfield *field) { switch (tag) { case TIFFTAG_ARTIST: return TIFFSetField(tif, tag, field->tfield_ARTIST.field1) case TIFFTAG_BADFAXLINES: return TIFFSetField(tif, tag, field->tfield_BADFAXLINES.field1) /* etc */ }l }; The tfield can be constructed in Haskell using the Storable mechanism. Hope this helps. Duncan