From david@cs.uow.edu.au Mon Dec  7 16:41:31 1992
Received: from calvin.sfasu.edu by umaxc.weeg.uiowa.edu (5.61.jnf/920629)
	  on Mon, 7 Dec 92 16:41:26 -0600 id AA11718 with SMTP 
Received: from wraith.cs.uow.edu.au by calvin.sfasu.EDU with SMTP (5.59/25-eef)
	id AA06260; Mon, 7 Dec 92 16:34:15 CST
Return-Path: <david@cs.uow.edu.au>
Received: by wraith.cs.uow.edu.au
	(5.65c/IDA-1.4.4); id AA21553; Tue, 8 Dec 1992 09:31:32 +1100
	(from david@cs.uow.edu.au for hyperC-l@calvin.sfasu.edu)
From: David E A Wilson <david@cs.uow.edu.au>
Message-Id: <199212072231.AA21553@wraith.cs.uow.edu.au>
Subject: findfirst & findnext - why opendir & friends.
To: hyperC-l@calvin.sfasu.edu (Hyper C Mailing List)
Date: Tue, 8 Dec 92 9:31:31 EST
Status: R

Forwarded message:
> As I'm Unix illiterate, please tell me whether the preference is one of
> substance or environmental familiarity.

Yes - I must admit up front to a bias in favour of UNIX. If I were an MS-DOS
programmer I would probably have stopped using my Apple //s many years ago.

> Perhaps, some reasons for the choice.  As we add more functions we'll soon
> come to point when we will have to decide if what we want HyperC to be is
> a Unix clone or some unrecognizable hybrid or ..... 

I would vote for a UNIX clone :-) but the following is sort of a defense.

Most C compilers provide a set of routines to emulate UNIX's open/read/write
& close interface so providing the opendir/readdir/closedir is in that spirit.
Most if not all C code I pull off Usenet is written to run under UNIX.

(I am not sure if any MS-DOS compilers provide this interface in addition to
the findnext style of interface).

>  
> >     struct dirent *readdir(dirp)
> >     DIR *dirp;
> > 
> I can make an educated guess at what the other functions do and I 
> _think_ I know what this one does, but can you elaborate?

It simply reads directory entries in sequence and returns them one at a time.
Here is an example from K&R 2.

Dirent *readdir(DIR *dp)
{
	static	direct	dirbuf;		/* local directory structure */
	static	Dirent	d;		/* return: portable structure */

	while (read(dp->fd, (char *) &dirbuf, sizeof(dirbuf)) == sizeof(dirbuf))
	{
		if (dirbuf.d_ino == 0)	/* slot not in use */
			continue;
		d.ino = dirbuf.d_ino;
		strncpy(d.name, dirbuf.d_name, DIRSIZ);
		d.name[DIRSIZ] = '\0';	/* terminate name */
		return &d;
	}
	return NULL;
}

Obviously this exact code will only work on a UNIX file system but a similar
routine for ProDOS should be quite easy.

Note:	The dirent vs direct is sysV vs BSD. I would lean towards dirent
	(but this is probably because Sun has moved to dirent.

Sample code which searchs a directory for entry ``name'' is:
 
	dirp = opendir(".");	/* pity Apple did not provide . & .. entries */
	for (dp = readdir(dirp); dp != NULL; dp = readdir(dirp))
	    if (!strcmp(dp->d_name, name)) {
		 closedir (dirp);
		 return FOUND;
	    }
	closedir (dirp);
	return NOT_FOUND;

>  
> >Under ProDOS they should not be very difficult at all to write. I might have
> >a go myself.
> Please do.  The approach looks elegant to this novice.

OK. Yet another project (fortunately this fits in nicely with another one).
-- 
David Wilson				+61 42 213802 voice, +61 42 213262 fax
Dept Comp Sci, Uni of Wollongong	david@cs.uow.edu.au