Hal Daume wrote:
I have a C function that, for simplicity, has its definition as something like:
void myCFun(FILE *fd);
I have a Handle I've opened in Haskell using openFileEx and would like to pass this to the function.
GHC's Handle type is based upon a descriptor rather than a FILE*, so you will have to manufacture the FILE*, e.g. with fdopen().
I've tried a bunch of things, the most recent being:
foreign import ccall "myHFile.h myCFun" c__myCFun :: Ptr CInt -> IO () myCFun :: Handle -> IO () myCFun (FileHandle handleMV) = do h__ <- readMVar handleMV ptr <- malloc poke ptr (toCInt $ haFD h__) c__initVars ptr
i've also tried it with just CInt -> IO (), without the ptr, but that doesn't work either.
Surely someone has done this at some point...or is it even possible (please say it is)...
For Unix, use Posix.handleToFd to get a descriptor, then fdopen() (in
C, or write a foreign import) to get a FILE*.
Also, don't forget about synchronisation issues between the C and
Haskell interfaces to the descriptor (e.g. buffering).
--
Glynn Clements