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3.5 Detailed rules for descriptors

These rules are intended to answer awkward questions.

  1. You can output to a descriptor only once.

  2. You can use a descriptor as an input many times.

  3. You can only output to a descriptor that was opened with modes "w", "t" and "p".

  4. You can only use a descriptor as input if it was opened with modes "r" or "rw".

  5. If you have output to a descriptor, you may subsequently use it as an input. "w" descriptors are automatically changed to "r" descriptors.

    If the function you are passing the descriptor to uses WIO (see §3.8.6), then "p" descriptors become "t". If the function you are passing the descriptor to uses PIO, then "p" descriptors are unchanged.



John Cupitt 2004-11-02