Path: utzoo!utgpu!jarvis.csri.toronto.edu!rutgers!cs.utexas.edu!sun-barr!oliveb!tymix!tardis!jms
From: jms@tardis.Tymnet.COM (Joe Smith)
Newsgroups: comp.sys.amiga.tech
Subject: Re: strins()
Summary: infinite loop using sprintf
Keywords: Lattice C Manx Aztec C strins() sprintf
Message-ID: <254@tardis.Tymnet.COM>
Date: 14 Jun 89 00:07:01 GMT
References: <0929.AA0929@caleb> <109394@sun.Eng.Sun.COM> <10285@watcgl.waterloo.edu>
Reply-To: jms@tardis.Tymnet.COM (Joe Smith)
Organization: McDonnell Douglas Field Service Co, San Jose CA
Lines: 22

[I predict there will be over 25 followups to Geo's article.]

In article <10285@watcgl.waterloo.edu> gswan@watcgl.waterloo.edu (Geo Swan) writes:
>Let me suggest that our original poster consider using the following macro:
>#define	strins( s1, s2 )	sprintf( s1, "%s%s", s2, s1 )

Can you guarantee that the above macro will work when s2 is longer than s1?
Example:  Let's say s1 is a pointer to an array of 80 bytes, and only the
first two bytes have any characters, the rest are null.  Let's say s2 is
a pointer to a string of 4 bytes.  As sprintf copies s2 into s1, it overwrites
the original string.  If sprintf copies until len(s1), then it will return
a pointer to an 8 byte string - s2 concatenated with s2.  If sprintf copies
until it gets to the null byte, it will never find it - s1 will get an
infinite number of copies of s2.  Or guru.

It's OK to use sprintf as long as the destination does not include any of
the sources.
-- 
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