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From: cziwkga AT pluto DOT ulcc DOT ac DOT uk (Kevin Ashley)
Newsgroups: comp.os.msdos.djgpp
Subject: Re: mkdir and errno in V2
Date: 21 Aug 1995 10:47:12 GMT
Organization: University of London Computer Centre
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In article <DDIw9C DOT MGD AT jade DOT mv DOT net>, Marc Singer <nbn.nbn.com!sapien!elf> writes:

|>It appears that the mkdir call does not clear errno on success. 
|>......
|>
|>Since it fails once, errno is ENOTDIR.  The successful mkdir calls do
|>not clear this value so errno on exit from my procedure is still
|>ENOTDIR.  I patch my procedure by clearing errno before each call to
|>mkdir.

mkdir is behaving correctly, although not in the way you and probably
many other people would like. errno only has a defined value after a
function call has failed and before you call any other function that
might affect errno. Succesful function calls are NOT required to
set errno to zero. The POSIX standard is quite explicit on this
(and mentions two exceptions - isatty and ptrace - one of which
isn't covered by POSIX anyway.)

Most functions which can set errno have some way of indicating
that they have returned with an error. errno is only valid if they
have so returned. In the case if mkdir, if it returns -1, then errno
is valid (i.e. contains a meaningful error code); if it returns 0, 
then it has succeeded and the value of errno is undefined. 

Your patch should be to test the return value of mkdir, then test
errno if the return value is -1. A conforming version of mkdir COULD
set errno to a non-zero value on success if it wished, and it's not
too difficult to imagine how this might happen. 
  
Kevin Ashley.
----------------------------------------------------------------------------
Kevin Ashley                              K DOT Ashley AT Ulcc DOT ac DOT uk
Systems Development Group Manager      http://www.ulcc.ac.uk/staff/Kevin+Ashley
University of London Computer Centre.      ...ukc!ncdlab!K.Ashley
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