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From: emf@eleazar.dartmouth.edu (Eric Friets)
Newsgroups: comp.lang.c
Subject: redirecting output
Message-ID: <23395@dartvax.Dartmouth.EDU>
Date: 27 Jul 90 15:17:13 GMT
Sender: news@dartvax.Dartmouth.EDU
Distribution: na
Organization: Dartmouth College, Hanover, NH
Lines: 32

A while ago I posted a request concerning redirecting
output in midprogram.  Thanks for the many responses;
the only workable one (received from a few netters) 
looks something like this: (the key is the dup2...)

int fdstdout,fdplot;

fflush(stdout);
fdplot=fopen("plot.out",O_WRONLY|O_CREAT,0644);
fdstdout=dup(1);
dup2(fdplot,1);
...
...
...
fflush(&_iob[fdplot]);
dup2(fdstdout,1);
close(fdplot);
close(fdstdout);

This works, but has a small glitch.  When unredirecting the
output (ie, sending to stdout instead of the file), a few
characters at the end of the file are corrupted.  Running
the program without this redirection results in the correct
output.  I tried pausing the program for a few seconds before
unredirecting, but this had no effect.

The computer is a SUN 3/160, running under the UNIX operating system.

Thanks,
Eric Friets
emf@eleazar.dartmouth.edu
.