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From: jik@athena.mit.edu (Jonathan I. Kamens)
Newsgroups: comp.unix.questions
Subject: Re: finding out if a directory is empty in C program
Message-ID: <1991May7.084438.16029@athena.mit.edu>
Date: 7 May 91 08:44:38 GMT
References: <900@homer.UUCP> <1991Apr15.180550.14750@beaver.cs.washington.edu> <1991Apr18.054735.6733@metapro.DIALix.oz.au> <1991Apr25.022029.5476@csc.canberra.edu.au> <1991Apr25.223540.19303@athena.mit.edu> <1991May3.155817.1807@visionware.co.uk>
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In article <1991May3.155817.1807@visionware.co.uk>, chris@visionware.co.uk (Chris Davies) writes:
|> >In article <1991Apr25.022029.5476@csc.canberra.edu.au>, rvp@softserver.canberra.edu.au (Rey Paulo) writes:
|> >|> Is there any system call or library routine in UNIX which tests whether
|> >|> a directory is empty?
|> In article <1991Apr25.223540.19303@athena.mit.edu> jik@athena.mit.edu (Jonathan I. Kamens) writes:
|> >No.  You open the directory with opendir() and read it, and if the only
|> >entries in it are "." and "..", it's empty.  Just like in a shell script
|> >(except the script uses ls, or shell wildcard expansion, instead of opendir()).
|> Why couldn't you use stat() and check whether the number of links == 2 ?
|> Most of the time it's not possible (well, not recommended) for _users_ to
|> hard-link to a directory, so the link-count wouldn't be wrong.

  First of all, only subdirectoris change the link count of a directory.  So
stat()ing the directory and checking its link count will detect only whether
or not it has subdirectories, not whether or not it is empty.

  Second, stat()ing and checking the link count to find out the number of
subdirectories is a hack that is not guaranteed to work on every system and
that is not required to work according to POSIX (at least, I don't think it
is, although I am interested in being corrected).   Operating Systems that
don't really put entries for "." and ".." in a directory (e.g. HP-UX, I
believe) will not have the link counts you're expecting.

  If you want to hard-code the special case operating systems in order to use
the stat() trick to check for subdirectories, you can, but the more reliable
way to do it is opening and reading the directory to see what's in it, and
ignoring "." and ".." if they show up.

-- 
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