building and analysing C structs with Storable
stefanor at cox.net
Sun Oct 14 15:23:00 EDT 2007
On Sun, Oct 14, 2007 at 09:19:24PM +0200, Henning Thielemann wrote:
> On Sat, 13 Oct 2007, Adam Langley wrote:
>> On 10/13/07, Henning Thielemann <lemming at henning-thielemann.de> wrote:
>>> Are there analogons to ByteString's Put and Get Monads to construct and
>>> disect binary data in a C struct for exchange with a C program?
>> The memory layout of structs depends on the ABI of system. You can
>> take a guess and write code in the Get and Put monads. Your guess will
>> probably work pretty well within a single architecture (e.g. x86 or
>> However, the portable way to do this is to get the information from
>> the C compiler, which is the approach that c2hs and friends use. I
>> would recommend this unless there's some good reason to think
>> otherwise. (see  for the exact hook)
>>  http://www.cse.unsw.edu.au/~chak/haskell/c2hs/
>>  http://www.cse.unsw.edu.au/~chak/haskell/c2hs/docu/c2hs-2.html#ss2.8
> I do not quite see the need for an extra tool. I thought it must be
> possible to ship a Haskell compiler with modules that depend on the
> system's C compiler, just like the modules that are implemented differently
> for Windows and Unix. Such modules could provide the functionality to
> create and inspect C structs for exchange with system libraries.
You say "the system's C compiler" as if there was only one. It's quite
common for UNIXoid systems to have several C compilers installed
simultaneously; and if you use the module corresponding to the wrong
compiler, you get silent data loss. I wouldn't risk it.
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