[Haskell-cafe] Help with c2hs, structs and typedefs?

[Magnus Jonsson]

In C, if you don't typedef the struct, the name of the struct is
"struct my_iovec_2", not "my_iovec_2". I don't know much about the
haskell FFI, but maybe this is the problem?

(by the way, why does "reply" default to replying to the sender, not
the mailing list?)

On Sun, Mar 8, 2009 at 1:25 PM, Antoine Latter <aslatter at gmail.com> wrote:
> Hey folks, I was trying to create some FFI bindings using c2hs and I
> ran into trouble: I can't use the 'sizeof' and 'set' hooks for structs
> that aren't defined inside a typedef.
>
> I don't know a whole lot about C - is there any declaration I can make
> to make something like my second struct work in c2hs?  Because the
> second struct is what's provided in <sys/uio.h> :-)
>
> In the following code, if you change all of the directives in the
> haskell code from my_iovec_2 to my_iovec, the "unknown indentifier"
> errors go away.
>
> Thanks,
> Antoine
>
>>>>>>
>
> -- Works!
> #c
> typedef struct {
>  void * my_iov_base;
>  int    my_iov_len;
> } my_iovec;
>
> #endc
>
> -- Broken!  I get lots of "unknown identifier" errors for
> -- the #sizeof and #set hooks - but the #pointer hook seems to work.
> #c
> struct my_iovec_2 {
>  void * my_iov_base;
>  int    my_iov_len;
> };
> #endc
>
> {#pointer *my_iovec_2 as IOVec newtype#}
>
> withIOVec :: [(Ptr a, CSize)] -> (Ptr IOVec -> Int -> IO b) -> IO b
> withIOVec [] f = f nullPtr 0
> withIOVec bufers f
>    = let len = length buffers in
>      alocaBytes (length bufers * {#sizeof my_iovec_2#}) $ \ptr ->
>      vecAry <- castPtr ptr
>      foldM (go vecAry) 0 bufers
>      f vecAry len
>
>  where go vecAry off (ptr, size) = do
>         vec <- vecAry `plusPtr` off * {#sizeof my_iovec_2#}
>         {#set my_iovec_2->my_iov_base#} vec $ castPtr ptr
>         {#set my_iovec_2->my_iov_len#}  vec $ cIntConv size
>         return $ off + 1
> <<<<<
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