Re: std::sort

From:
Mark P <usenet@fall2005REMOVE.fastmailCAPS.fm>
Newsgroups:
comp.lang.c++
Date:
Mon, 26 Nov 2007 22:38:39 GMT
Message-ID:
<PVH2j.71412$YL5.59686@newssvr29.news.prodigy.net>
Jeff Schwab wrote:

Would std::sort ever compare an object with itself? I'm not talking
about two distinct, equal-valued objects, but rather this == &that.
The container being sorted is a std::vector.

I've never seen this, but a coworker says he is. NB: I can't post
sample code that reproduces the issue, nor do I claim any bug in the
STL implementation (GCC 3.4.2). I'm just hoping a definitive answer
resides in one of the brains who frequent this group.


Well, first of all note that std:sort doesn't use == for comparison. It
either uses operator< or, optionally, a user-specified comparison
functor. Now with the understanding that, for sort, "a == b" means both
a < b and b < a are false...

I can't think of any reason why it *would* compare an object with
itself, but I don't know any reason why it *can't*. This ought to be
easy to check for your specific implementation by either looking at the
header file or by writing a comparison functor that will report if this
happens.

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