Dnia śro 4. czerwca 2003 14:16, Bayley, Alistair napisał:
Is alloca the idiomatic technique when you want to create a pointer to a pointer? Or are there other ways?
It's an idiomatic technique for creating a temporary C object whose lifetime is explicit. You could use malloc, but then you have to remember to free it. alloca is an analogue of local variables in C (they are really allocated on GHC heap in GHC or with malloc in other implementations).
Initially I tried to pass a Ptr (Ptr SomeType), but I couldn't because Ptr has no constructors To create values of type Ptr I must use the functions in Foreign.Marshal.Alloc (and Foreign.Marshal.Utils). Correct?
More or less yes (there is nullPtr, you can 'foreign import' pointers to global C variables, you can return pointers from imported C functions if it makes sense...). -- __("< Marcin Kowalczyk \__/ qrczak@knm.org.pl ^^ http://qrnik.knm.org.pl/~qrczak/