I think this is relation to my problem. I wnant to write Haskell interface to FFmpeg. So first, I try to port output_example.c to Haskell. But output_example.c's wants to initialize structure like this, void write_audio_frame(AVFormatContext *oc, AVStream *st) { int out_size; AVCodecContext *c; AVPacket pkt; av_init_packet(&pkt); c = &st->codec; get_audio_frame(samples, audio_input_frame_size, c->channels); pkt.size= avcodec_encode_audio(c, audio_outbuf, audio_outbuf_size, samples); pkt.pts= c->coded_frame->pts; pkt.flags |= PKT_FLAG_KEY; pkt.stream_index= st->index; pkt.data= audio_outbuf; /* write the compressed frame in the media file */ if (av_write_frame(oc, &pkt) != 0) { fprintf(stderr, "Error while writing audio frame\n"); exit(1); } } then I need to return a structure. But I know that : On Wed, 02 Mar 2005 14:45:54 +1100, Ben Lippmeier wrote:

No. The way data is organised in memory is dramatically different in Haskell when compared with C. You need to write functions to read in each field in turn and then "reconstruct" the structure on the Haskell side.

It's a tedious process. My advice is that if you have a lot of structures to read, write a (simple) preprocessor to generate the marshalling code.. that's what I did.

so I wrote a code like this, (This use hsc2hs to write "read and write each field".) ----------------------------------------------------------------------------- -- -*- mode: haskell -*- {-# OPTIONS -fglasgow-exts #-} #include #include module FFmpeg where import Foreign data CAVPacket = CAVPacket {pktPts :: !(#type int64_t), pktDts :: !(#type int64_t), pktDatas :: !(Ptr (#type uint8_t)), pktSize :: !Int, pktStreamIndex :: !Int, pktFlags :: !Int, pktDuration :: !Int} deriving (Eq,Show) instance Storable CAVPacket where peek p = do{ pts <- (#peek AVPacket, pts) p; dts <- (#peek AVPacket, dts) p; datas <- (#peek AVPacket, data) p; size <- (#peek AVPacket, size) p; stream_index <- (#peek AVPacket, stream_index) p; flags <- (#peek AVPacket, flags) p; duration <- (#peek AVPacket, duration) p; return $! CAVPacket pts dts datas size stream_index flags duration } poke p (CAVPacket pts dts datas size stream_index flags duration) = do{(#poke AVPacket, pts) p pts; (#poke AVPacket, dts) p dts; (#poke AVPacket, data) p datas; (#poke AVPacket, size) p size; (#poke AVPacket, stream_index) p stream_index ; (#poke AVPacket, flags) p flags; (#poke AVPacket, duration) p duration} sizeOf _ = (#size AVPacket) -- I don't confident this value. alignment _ = 7 av_init_packet :: IO (Ptr CAVPacket) av_init_packet = alloca $ \pkt -> do c_av_init_packet pkt return pkt foreign import ccall unsafe "av_init_packet" c_av_init_packet :: Ptr CAVPacket -> IO () ----------------------------------------------------------------------------- but ghc-6.2.2 said : FFmpeg.o(.text+0x44):fake: undefined reference to `av_init_packet' . Of cource, this problem is only here, ghc can refers to other C function by FFI. And if I don't pass the link option to ghc, then ghc's refer problem message is normaly, like this : c:/ghc/ghc-6.2.2/libHSrts.a(Main.o)(.text+0x87):Main.c: undefined reference to `__stginit_ZCMain' Where is a problem of my code? -- shelarcy <shelarcy capella.freemail.ne.jp> http://page.freett.com/shelarcy/