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? Thanks, Bryan Green *************************************************************************** The information contained in this communication is confidential, is intended only for the use of the recipient named above, and may be legally privileged. If the reader of this message is not the intended recipient, you are hereby notified that any dissemination, distribution or copying of this communication is strictly prohibited. If you have received this communication in error, please resend this communication to the sender and delete the original message or any copy of it from your computer system. Thank You. ****************************************************************************
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
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Duncan Coutts -
Green Bryan - bgreen