Re: Visual C++ Express won't compare object against float in std::upper_bound

From:
Ulrich Eckhardt <eckhardt@satorlaser.com>
Newsgroups:
microsoft.public.vc.stl
Date:
Fri, 23 Feb 2007 09:51:56 +0100
Message-ID:
<dim2b4-dt7.ln1@satorlaser.homedns.org>
tron.thomas@verizon.net wrote:
[about use of std::upper_bound]

I added two member function to the class. One to compare if a Sample
was less than a float, and another to compare if a Sample was less
than another Sample. That solved the problem.

What I'm wondering now is why adding that additional members was
necessary, because on two other compilers the member wasn't
necessary. I'm curious as to whether then isn't a bug in one or more
of these compilers or their implementations of the STL.


It's non-normative, but take a look at the docs[1] at SGI's. It explicitly
states as a requirement that the iterator's value type must be the same as
the compared value's type. You are mixing an iterator over Samples with a
value of type float.

In any case, it does make sense that if the algorithm allows mixing those as
an extension, the less-than-comparable requirement must hold for all
combinations of them, i.e. you must be able to use both types freely on
both sides of the comparison.

In case that isn't clear, the compiler will not use operator> and == to form
an alternate form of operator< when that is not available!

Uli

[1] http://www.sgi.com/tech/stl/upper_bound.html

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