printf("foobar\n");
if(fork() == 0)
exit(0);n fork() calls and there were exactly n additional copies of the output). After a bit of digging around and not finding any obvious fault, I asked about it on IRC.It turned out that
stdout is fully buffered when it is attached to a pipe or a file. What happened is that fork() duplicated also the internal I/O buffers, which got flushed after the child process exited, thus producing extra output. I solved the problem by inserting a fflush(NULL); statement before forking, which flushes buffers of all output streams.
2 comments:
Note that a much better solution is to never use exit() in the child process. Use _exit() instead, this is exactly what it's for.
Libraries may be adding other code using atexit() behind your back, and you'll run into problems. I learned that the hard way, when a GUI program I was working on forked kept losing connections to the X server. It turned out that Xlib had an atexit() handler that notified the X server that the client was exiting. Since the child inherits all file descriptors, exit() in the child broke the parent's X connection.
In your case you probably need both if the child is doing its own printing to stdout.
The documentation says that it is implementation-defined whether _exit() flushes open output streams. So, your solution won't work.
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