Date: Thu, 10 Sep 1998 02:36:01 +0100 From: Brian Somers <brian@Awfulhak.org> To: Mark Ovens <marko@uk.radan.com> Cc: questions@FreeBSD.ORG, freebsd-users@freebsd-uk.eu.org Subject: Re: Help needed with fork(), pipe() & dup2() Message-ID: <199809100136.CAA05582@woof.lan.awfulhak.org> In-Reply-To: Your message of "Wed, 09 Sep 1998 21:08:08 -0000." <35F6EE38.7DC97F21@uk.radan.com>
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[.....]
> void foo()
> {
> char line [MAX_LINE];
> int fd [2];
> pid_t pid;
>
> pipe(fd);
> if ((pid = fork ()) < 0)
> error_message();
> else
> if (pid > 0)
> { /* parent */
> close (fd [1]);
> if (fd [0] != STDIN_FILENO)
> {
> dup2(fd [0], STDIN_FILENO)
> close (fd [0]);
> }
> /* read file names from pipe */
> while (gets (line) != NULL)
> {
> .
> .
> code to process "line" here
> .
> .
> }
>
> close (fd [0]);
^^^^^^^^^^^^^^^
Dodgy - fd[0] has already been closed (unless == STDIN_FILENO).
> } /* parent */
> else
> { /* child */
> close (fd [0]);
> if (fd [1] != STDOUT_FILENO)
> {
> dup2(fd [1], STDOUT_FILENO)
> close (fd [1]);
> }
> if (execvp ("file", files) < 0)
> error_message ();
> close (fd [1]);
Ditto, but this one (hopefully) doesn't normally happen. You're also
missing an exit() here.
> } /* child */
> }
I don't know enough about the rest of the code to tell if that first
close may be the problem - but it *might*. Also, are you sure that
last error_message() isn't being called ?
--
Brian <brian@Awfulhak.org>, <brian@FreeBSD.org>, <brian@OpenBSD.org>
<http://www.Awfulhak.org>;
Don't _EVER_ lose your sense of humour....
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