[Haskell-cafe] How can I redirect stdout?
mattcbro at earthlink.net
Fri Sep 29 14:44:58 EDT 2006
I'm reposting this in it's own new thread since I think it involves a
general issue beyond exporting Haskell DLLs.
I am having some problems with GHCs stdout when a Haskell program is
called from a windows program.
As I noted earlier I am calling some Haskell code from C as a bridge to
being able to
ultimately call Haskell from Matlab 6.5.
The Haskell code is compiled into a .DLL file on a windows machine.
Matlab calls some C code which then calls the Haskell code.
As soon as it gets into the Haskell code I get this run time error in
<stdout>: hPutChars: invalid argument (Bad File Descriptor)
The Haskell code seems to work correctly if called from a stand-alone C
program. Moreover, if I scrub all print statements from the Haskell
code, it appears to run correctly from Matlab.
Matlab does not properly redirect stdout so any printf calls from the C
code simply fail to print.
However Haskell's behavior is to halt after generating a runtime error.
The C code used to generate the Haskell .dll is of course mingw gcc, but
the C code used to create my Matlab mex file is Microsoft VC++ 6.0. I
tried to redirect stdout using freopen() in C, but that never seems to
work with Microsoft. At any rate it certainly doesn't effect Haskells
use of stdout. I think in general for windows programs there is no
stdout defined, whereas it's always defined for console programs.
My question is, is there some way I can redirect stdout from inside
Haskell so that all output is sent to a file? Is there an equivalent of
freopen() in Haskell that works?
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