Path: utzoo!attcan!uunet!munnari!otc!metro!ipso!runx!brucee
From: brucee@runx.ips.oz (Bruce Evans)
Newsgroups: comp.os.minix
Subject: Bugs in 'strn' library functions
Message-ID: <1518@runx.ips.oz>
Date: 15 May 88 13:43:25 GMT
Organization: RUNX Un*x Timeshare.  Sydney, Australia.
Lines: 41


The 'strn' functions in the Minix 1.2 library *all* diverge from the V7
standard. I think that means they are broken.

strncpy( char *t, char *s, int n )
-------

Supposed to copy *exactly* n characters, truncating or *null padding* as
necessary. The target need *not* be null-terminated.

Actually copies at most (n + 1) characters and doesn't null pad more than
once. Always null terminates the string, thereby copying 1 too many in
some cases. Treats zero counts as 64K and negative counts as unsigned.
(I've always thought counts should be unsigned, but that's not the
standard).

strncat( char *t, char *s, int n )
-------

Supposed to copy *at most* n characters. The target need *not* be
null-terminated.

Always null terminates the string, thereby copying 1 too many in some
cases. Treats zero count correctly but negative counts as unsigned.

strncmp( char *s1, char *s2, int n )
-------

Supposed to compare at most n characters.

Treats zero count as 64K and negative counts as unsigned.

---

I can easily post correct versions (in C and 2+ different non-Minix
assembly languages yet), but I'm more worried about the correctness
of the library generally, since there is nothing much easier or
better documented than strncpy. (Perhaps the precise documentation
is the problem?) (:-).

Bruce Evans
Internet: brucee@runx.ips.oz.au    UUCP: uunet!runx.ips.oz.au!brucee