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From: gbs@voder.UUCP (George Smith)
Newsgroups: comp.sys.ibm.pc
Subject: Re: DOS patches
Message-ID: <2947@voder.UUCP>
Date: Mon, 1-Jun-87 13:11:38 EDT
Article-I.D.: voder.2947
Posted: Mon Jun  1 13:11:38 1987
Date-Received: Wed, 3-Jun-87 01:38:26 EDT
References: <923@wjvax.wjvax.UUCP> <656@custom.UUCP>
Organization: National Semiconductor, Santa Clara
Lines: 46
Summary: what is the DOS internal size of filenames?

In article <656@custom.UUCP>, boykin@custom.UUCP (Joseph Boykin) writes:
> In article <923@wjvax.wjvax.UUCP>, curl@wjvax.UUCP (Jim Curl) writes:
> > I'm looking for ways to patch DOS in order to do two things:
> >     (1) I'd like to be able to have a longer PATH than the 128 or so
> >         characters now allowed -- this limitation might be a function
> >         of my editor?
> 
> 1) DOS has an internal limit of 64 characters for any single
> directory name (see documentation on System call # 3bH).
> ...
> Joe Boykin
> Custom Software Systems
> ...necntc!custom!boykin

It's interesting - there seems to be some looseness on the part of IBM
with regard to their definition of the size of a path name passed to a
DOS function.  As pointed out by Joe Boykin, chdir (int 21h, function 3bh)
makes mention of the 64 character limit on the size of the ASCIIZ string
which is to contain the path name.

However, the following functions which also expect an ASCIIZ string with
the path name DON'T mention the 64 character limit:

	mkdir  (39h)		chmod      (43h)
	rmdir  (3ah)		exec       (4bh)
	creat  (3ch)		find first (4eh)
	open   (3dh)		find next  (4fh)
	unlink (41h)		rename     (56h)

Also, the definition of an ASCIIZ string (page 6-46, DOS Tech Ref, v3.20)
says "The maximum size of an ASCIIZ string is 128 bytes, including the
drive, colon, and null terminator).

Finally, function get current directory (47h), specifies DS:SI must point
to a 64-byte user memory area.  It will place the full path name of the
current directory for the specified drive there.  This seems to back
Joe's statement.

Why do the two directory functions (CHDIR and Get Current Directory)
specifically mention a 64 char limit vs the ASCIIZ definition and the
lack of specifiying any size for the other functions?

-- 
George B. Smith
National Semiconductor
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