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From: kemnitz@mitisft.Convergent.COM (Gregory Kemnitz)
Newsgroups: comp.unix.wizards
Subject: Re: Dot files always first in directory?
Summary: Unportable code alert!!
Message-ID: <672@mitisft.Convergent.COM>
Date: 4 May 89 20:19:25 GMT
References: <11108@bloom-beacon.MIT.EDU>
Organization: Convergent Technologies, San Jose, CA
Lines: 46

In article <11108@bloom-beacon.MIT.EDU>, jik@athena.mit.edu (Jonathan I. Kamens) writes:
> 
> It it safe to assume when writing a program which manipulates
> directories that . and .. will always be the first two entries in a
> directory?
> 
> If I can't assume that, then I've got to compare every file in the
> directory to "." and "..", and this would probably slow the program
> down even more than it already is.
> 

After checks on our file system, I found that this assumption is PROBABLY
correct.  However, this type of thing is EXTREMELY DANGEROUS, unless it is
part of the definition of the directory structure (It might well be - if it
is ignore this message and I'll be eating flames).  This type of assumption
usually leades to unportable code. (will your code run on UNIX forever??)

A portable way to implement this assumption (without error checking for
clarity):

struct dirent (direct??) *dir1, *dir2;
BOOLEAN dot_and_dotdot_read;

dir1 = readdir(dirp);
dir2 = readdir(dirp);

dot_and_dotdot_read = (!strcmp(dir1->file_name, ".")
                      && !strcmp(dir2->file_name, ".."))
                   || (!strcmp(dir1->file_name, "..")
                      && !strcmp(dir2->file_name, ".");

if (dot_and_dotdot_read) 
{
     proceed using assumption...
}
else
{
     proceed carefully.  Remember to process dir1 and dir2
}

I may be wrong about the members of the structures, but you get the point.
Also, I omitted error checking.  In any code of this type, you should always
check the return value. 


				Greg Kemnitz