CODEWITHSUNDEEP
c
mandez
mandez

Reputation: 137

Closing and reopening piped file descriptors for writing in c

I have a question please regarding what happens if I closed a file descriptor after writing into it ( e.g fd[1] after piping fd ), then opened it again to write. Will the data be overwritten and all the previous ones will be gone or it will keep on writing from the end point it stopped at after the first write? I used the system call open() with the file descriptor and no other arguments.

Upvotes: 0

Views: 903

Answers (1)

Jonathan Leffler
Jonathan Leffler

Reputation: 755026

If you close either of the file descriptors for a pipe, it can never be reopened. There is no name by which to reopen it. Even with /dev/fd file systems, once you close the file descriptor, the corresponding entry in the file system is removed — you're snookered.

Don't close a pipe if you might need to use it again.

Consider whether to make a duplicate of the pipe before closing; you can then either use the duplicate directly or duplicate the duplicate back to the original (pipe) file descriptor, but that's cheating; you didn't actually close all the references to the pipe's file descriptor. (Note that the process(es) at the other end of the pipe won't get an EOF indication because of the close — there's still an open file descriptor referring to the pipe.)

Upvotes: 3

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