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Date: Tue, 21 Aug 2001 00:12:36 +1000 (EST)
From: Bruce Evans <bde@zeta.org.au>
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To: Maxim Sobolev <sobomax@FreeBSD.org>
Cc: Brian Somers <brian@FreeBSD.org>, <kris@FreeBSD.org>,
	<cvs-committers@FreeBSD.org>, <cvs-all@FreeBSD.org>
Subject: Re: cvs commit: src/sbin/newfs mkfs.c src/sbin/ping6 ping6.c
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On Mon, 20 Aug 2001, Maxim Sobolev wrote:

> > brian       2001/08/20 05:56:45 PDT
> >
> >   Modified files:
> >     sbin/newfs           mkfs.c
> >     sbin/ping6           ping6.c
> >     sbin/route           route.c
> >   Log:
> >   Handle snprintf() returning -1.
>
> What is condition for snprintf() returning -1? The manpage doesn't provide
> any clue, so as the SUSv2 specification. Perhaps manpage should be extended
> to be more clear in this area.

In C99:
- if an encoding error occurred (then the return value may be any negative
  int, so checking for -1 is incorrect).

In FreeBSD:
- if the result is not representable as a (non-negative) int, then -1 is
  returned without changing errno.  Example: format "foo%*s" with a
  preposterously larger field width.
- I think encoding errors can't occur, because FreeBSD doesn't really support
  wide character stuff.

In POSIX.1-200x:
- as in C99, plus:
- if the buffer size or the result is not representable as a (non-negative)
  int, then a negative value is returned and errno is set to EOVERFLOW.

I think the buffer contents is indeterminate when snprintf() returns < 0,
so the buffer might not be NUL-terminated.  Some of Brian's changes didn't
seem to handle this right.  But the best way to handle snprintf() returning
< 0 may be to crash.

Bruce


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