[Haskell-cafe] Writing binary files?

[Abraham Egnor]

Passing a Ptr isn't that onerous; it's easy enough to make functions
that have the signature you'd like:

import System.IO
import Data.Word (Word8)
import Foreign.Marshal.Array

hPutBytes :: Handle -> [Word8] -> IO ()
hPutBytes h ws = withArray ws $ \p -> hPutBuf h p $ length ws

hGetBytes :: Handle -> Int -> IO [Word8]
hGetBytes h c = allocaArray c $ \p ->
    do c' <- hGetBuf h p c
       peekArray c' p


On Sun, 12 Sep 2004 14:24:56 +0100, Glynn Clements
<glynn.clements at virgin.net> wrote:
> 
> Sven Panne wrote:
> 
> > > [...]
> > >     main :: IO ()
> > >     main = do
> > >             h <- openBinaryFile "out.dat" WriteMode
> > >             hPutStr h $ map (octetToChar . bitsToOctet) bits
> > >             hClose h
> >
> > Hmmm, using string I/O when one really wants to do binary I/O gives me a bad
> > feeling. Haskell characters are defined to be Unicode characters, so the
> > above only works because current Haskell implementations usually get this wrong
> > (either no Unicode support at all and/or ignoring any encodings and doing I/O
> > only with the lower 8 bits of the characters)... hGetBuf/hPutBuf plus their
> > non-blocking variants are the only way to *really* do binary I/O currently.
> 
> Which is unfortunate, because of the requirement to pass a Ptr. We
> really need "hPutBytes :: [Word8] -> IO ()" etc.
> 
> Also, changing the existing functions to deal with encodings is likely
> to break a lot of things (i.e. anything which reads or writes data
> which is in neither UTF-8 nor the locale-specified encoding).
> 
> 
> 
> --
> Glynn Clements <glynn.clements at virgin.net>
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