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POReading from a pipe to my child process
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  1. POReading from a pipe to my child process
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    copied!<p>Hopefully a simple question. I'm trying to learn, simultaneously, fork(), pipe(), and waitpid() and running into some problems.</p> <pre><code>if (pipe(myout)&lt;0 || pipe(myin)&lt;0 || pipe(myerr)&lt;0) { perror("Couldn't make pipes"); return; } int childpid=fork(); if (childpid==0) { //child fdopen(myout[1], "w"); fdopen(myin[1], "r"); fdopen(myerr[1], "w"); dup2(myout[1], 1); dup2(myin[1], 0); dup2(myerr[1], 2); printf("This should be seen\n"); fclose(stdout); fclose(stdin); fclose(stderr); sleep(10); _exit(0); } else { //parent, wait on child printf("parent, monitoring\n"); sim_out=fdopen(myout[0], "r"); sim_in=fdopen(myin[0], "w"); sim_err=fdopen(myerr[0], "r"); printf("have my fds\n"); int status; do { int ch; if (read(myout[0], &amp;ch, 1)&gt;0) write(1, &amp;ch, 1); else printf("no go\n"); waitpid(childpid, &amp;status, WNOHANG); } while (!WIFEXITED(status) &amp;&amp; !WIFSIGNALED(status)); } </code></pre> <p>I'm getting:</p> <blockquote> <p>parent, monitoring have my fds T</p> </blockquote> <p>before the program exits - that is, the loop runs only once. I have a check below that, and it's coming up WIFEXITED() so the process is supposed to have exited normally. But what bothers me is that there's a sleep(10) before that happens, and this happens immediately - not to mention that the child processes are left running for the remaining wait time.</p> <p>I'm fundamentally misunderstanding something, clearly. My expectation was that the parent loop would block until it sees a character from the child, read it, then check to see if it was still alive. I certainly didn't expect waitpid() to set WIFEXITED when the child was still alive.</p> <p>Where am I wrong?</p>
 

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