Okay, okay, I'm convinced that trying to mess with it in C is easier than in Haskell. =P
Louis Wasserman wasserman.lo...@gmail.com http://profiles.google.com/wasserman.louis On Fri, Feb 26, 2010 at 2:14 PM, Brandon S. Allbery KF8NH < allb...@ece.cmu.edu> wrote: > On Feb 26, 2010, at 14:44 , Louis Wasserman wrote: > > Is there any way I can temporarily reassign stdout? In particular, will > this be handled well by the FFI? I'm hoping there's maybe something like > PHP's output buffering thingy<http://php.net/manual/en/book.outcontrol.php>. > I'm *binding* (not doing a process call) to an external library which > outputs directly to stdout, but whose output I'd like to use... > > > That way lies pain. It can be done, but if it breaks it will break rather > thoroughly and leave you stranded. Untested (aside from compilation), no > warranty, etc.: > > module Redirect (withRedirectedStdout) where > > import System.IO > import System.Posix.IO > > -- usage: withRedirectedStdout destinationFileName $ yourIOActionHere > -- this might work with Haskell I/O, if you're lucky; don't bet on it > -- stick to FFI calls that use raw I/O > withRedirectedStdout :: FilePath -> IO a -> IO a > withRedirectedStdout f io= do > hFlush stdout > -- style note: should be stdOutput but that doesn't work for the binds > -- and I'm not sure it's worth doing those "right". maybe if someone > wants this > -- for the library I'll clean it up > old <- dup 1 > closeFd 1 > -- this will pattern-match fail if we don't get stdout back; if you > manage to trigger it, > -- you get to keep both pieces. (you probably closed stdin, which is > usually a > -- recipe for disaster, or at minimum extreme confusion) > 1 <- openFd f WriteOnly (Just 0600) (defaultFileFlags {noctty = True, > trunc = True, nonBlock = False}) > res <- io > closeFd 1 > 1 <- dup old > closeFd old > return res > > Actually, I bet this fails because your FFI function uses C/C++ stdio and > doesn't flush it. That will probably require bringing in C stdio's > fflush(stdout), which will be even more painful. > > -- > brandon s. allbery [solaris,freebsd,perl,pugs,haskell] allb...@kf8nh.com > system administrator [openafs,heimdal,too many hats] allb...@ece.cmu.edu > electrical and computer engineering, carnegie mellon university KF8NH > > >
_______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
