Re: Restrictions on qsort compare function?

Article View: comp.std.c

Article #4934

#4934

From: Mark Brader
Date: Fri, 22 Mar 1996 20:40

17 lines
1170 bytes

> Alternatively, how about this:
> 
>     return ((signed int) ((unsigned int)a - (unsigned int)b));

Assuming that a and b are int, this line cannot produce undefined
behavior, but if a < b, the value returned is implementation-defined
and in particular its sign is not specified by the standard.

If the implementation allows this returned value to be non-negative
for some values of a and b, then the function is not a legitimate
comparison function for qsort() because it may not be transitive.
Therefore the code is not strictly conforming.
-- 
Mark Brader, msb@sq.com        "do right; have fun; make money"
SoftQuad Inc., Toronto              -- Ian Darwin on Yuri Rubinsky (1952-96)

My text in this article is in the public domain.

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Newsgroups: comp.std.c
Path: arc1-ca.pugleaf.net!nntp.coast.net!torn!sq!msb
From: msb@sq.com (Mark Brader)
Subject: Re: Restrictions on qsort compare function?
Message-ID: <1996Mar22.204023.10235@sq.com>
Organization: SoftQuad Inc., Toronto, Canada
References: <4iokop$h4p@lyra.csx.cam.ac.uk> <1996Mar21.113301.2622@sq.com> <4it51b$ng8@usenet.pa.dec.com> <4iukhc$5nr@rdsunx.crd.ge.com>
Date: Fri, 22 Mar 1996 20:40:23 GMT

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