From mboxrd@z Thu Jan  1 00:00:00 1970
From: David Lee <live4thee@gmail.com>
Subject: Re: Help on pipe
Date: Fri, 10 Jul 2009 15:27:07 +0800
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To: Ardhan Madras <nightdecoder@gmail.com>
Cc: linux-c-programming@vger.kernel.org

On Fri, Jul 10, 2009 at 2:22 PM, Ardhan Madras<nightdecoder@gmail.com> =
wrote:
> Hi,
>
> I'm writing pipe demo:
>
> #include <sys/types.h>
> #include <sys/wait.h>
> #include <unistd.h>
> #include <stdio.h>
> #include <string.h>
>
> int main(void)
> {
> =A0pid_t pid;
> =A0int fds[2], ret;
> =A0const char *sort =3D "/usr/bin/sort";
> =A0char *argv[2] =3D { "sort", NULL };
>
> =A0ret =3D pipe(fds);
> =A0if (ret =3D=3D -1) {
> =A0 =A0perror("pipe");
> =A0 =A0return -1;
> =A0}
> =A0pid =3D fork();
> =A0if (pid =3D=3D -1) {
> =A0 =A0perror("fork");
> =A0 =A0return -1;
> =A0}
>
> =A0if (pid =3D=3D 0) {
> =A0 =A0int ret;
>
> =A0 =A0close(fds[1]);
> =A0 =A0dup2(fds[0], STDIN_FILENO);
>
> =A0 =A0ret =3D execve(sort, argv, NULL);
> =A0 =A0if (ret =3D=3D -1) {
> =A0 =A0 =A0perror("execve");
> =A0 =A0}
> =A0 =A0close(fds[0]);
> =A0 =A0_exit(0);
> =A0}
> =A0else {
> =A0 =A0FILE *stream;
>
> =A0 =A0close(fds[0]);
> =A0 =A0stream =3D fdopen(fds[1], "w");
> =A0 =A0if (!stream) {
> =A0 =A0 =A0perror("fdopen");
> =A0 =A0 =A0return -1;
> =A0 =A0}
> =A0 =A0fprintf(stream, "this\n");
> =A0 =A0fprintf(stream, "means\n");
> =A0 =A0fprintf(stream, "war\n");
> =A0 =A0fflush(stream);
> =A0 =A0waitpid(pid, &ret, 0);
> =A0 =A0close(fds[1]);
> =A0}
> =A0return 0;
> }
>
> I want to send parent's data to the child as "sort" input, i don't
> know why sort doesn't receive the data. Did i made mistake here?
>
> Thanks before.
> --
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>

The sort program is waiting for an EOF (^D).

--- sort.c.orig 2009-07-10 15:54:36.000000000 +0800
+++ sort.c      2009-07-10 15:53:35.000000000 +0800
@@ -49,6 +49,7 @@
                fprintf(stream, "means\n");
                fprintf(stream, "war\n");
                fflush(stream);
+              fclose(stream);
                waitpid(pid, &ret, 0);
                close(fds[1]);
        }


--=20
Thanks,
Li Qun
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