On 21 October 2005 14:40, Joel Reymont wrote:
I stumbled upon this when binding the Zlib library and want to make sure I'm doing this right.
foreign import ccall unsafe "uncompress" uncompress_ :: Ptr Word8 -> Ptr CULong -> Ptr Word8 -> CULong -> IO CInt
You give this function the address of your size as second argument and it updates size for you. basic uncompress(char* buf, unsigned long *size, ...) for you.
Is it correct that I need to allocate a chunk of 4 bytes to be passed into C and updated there and then need to peek my value from that chunk of memory?
yes, something like with $ \pculong -> r <- uncompress_ buf pculong ... size <- peek pculong
I thought StablePtr would give me the address of a Haskell value but it gives me an offset into some table instead.
That's right, the reason being that Haskell values move around when GC happens. Cheers, Simon