Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!ukma!rutgers!bpa!cbmvax!ditto
From: ditto@cbmvax.UUCP (Michael "Ford" Ditto)
Newsgroups: comp.bugs.4bsd
Subject: Re: ungetc will put characters back into an _IOSTRG input stream
Summary: Alternative code
Keywords: writable strings, shared strings (text segment), sscanf, ungetc
Message-ID: <5969@cbmvax.UUCP>
Date: 14 Feb 89 02:43:58 GMT
References: <20282@lll-winken.LLNL.GOV>
Reply-To: ditto@cbmvax.UUCP (Michael "Ford" Ditto)
Organization: Commodore Technology, West Chester, PA
Lines: 21

In article <20282@lll-winken.LLNL.GOV> casey@lll-crg.llnl.gov (Casey Leedom) writes:
>	! 	if (iop->_flag & _IOSTRG)
>	! 		--iop->_ptr;
>	! 	else
>	! 		*--iop->_ptr = c;

As an alternative to the above four lines, why not:

	if (*--iop->_ptr != (char)c)
		*iop->ptr = c;

This will give anyone ungetc'ing something weird into a readonly string
the segmentation fault they deserve, and still allow ungetc'ing into
a writable string (even though nobody should be doing that).
-- 
					-=] Ford [=-

"The number of Unix installations	(In Real Life:  Mike Ditto)
has grown to 10, with more expected."	ford@kenobi.cts.com
- The Unix Programmer's Manual,		...!sdcsvax!crash!elgar!ford
  2nd Edition, June, 1972.		ditto@cbmvax.commodore.com