typedef struct { int *a; int *b; /*lots of stuff ... */ int *z; } foo; int create_foo(foo *f,FILE *file,int x,int y); int use_foo(foo *f,int w); int destroy_foo(foo *f);
newtype Foo = Foo () foreign import ccall "static foo.h create_foo" c_create_foo :: Ptr (Foo) -> Ptr (CFile) -> CInt -> CInt -> IO CInt foreign import ccall "static foo.h use_foo" c_use_foo :: Ptr (Foo) -> CInt -> IO CInt foreign import ccall "static foo.h destroy_foo" c_destroy_foo :: Ptr (Foo) -> IO CInt
Your 'create_foo' is only an initialization function, i.e., it initializes data in a Foo but do not allocate memory for the data such pointer points to. So, what you would like to do is something like this: import Foreign.Marshall.Alloc (...) ptrFoo <- malloc c_create_foo ptrFoo ptrCFile (...) (...) free ptrFoo Looking at malloc you see: malloc :: Storable a => IO (Ptr a) and this gives you the hint: you need to make an instance of Storable class with your Foo type. Storable method 'sizeOf' should provide the proper size to be used in such kind of memory allocation. (After that, you would probably want to learn about ForeignPtr, which would call, say, free and c_destroy_foo when your pointer is not beeing used anymore.) Best, Maurício P.S.: (Warning: spam promoting my own work.) If you use my package bindings-common, available in hackage, you can get that type and instance in a .hsc file by doing this: #bindings_starttype struct foo #bindings_stoptype _ But this package is not very popular yet, so I can't guarantee it's bug free.