Re: BinaryPredicate Question

From:
"Daniel T." <daniel_t@earthlink.net>
Newsgroups:
comp.lang.c++.moderated
Date:
Sat, 27 Jan 2007 23:13:41 CST
Message-ID:
<daniel_t-A934D1.18535027012007@news.west.earthlink.net>
"James Kanze" <james.kanze@gmail.com> wrote:

Otis Bricker wrote:

I'm trying to figure out is the following technique is valid.

Given
std::vector<DataItem> cache;

which is sorted by the ID_ field of each DataItem.

And this Predicate class:

class IdLessThan: public std::binary_function<long, DataItem, bool>
{
public:
    bool operator()
     ( long lhs, const DataItem& rhs)const{return lhs <
rhs.ID_;};
};

Is the following valid?

Vector<DataItem>::iterator it =
     std::upper_bound(cache.begin(),cache.end(),ID, IdLessThan());


No. Given this call, IdLessThan must be callable with a first
argument of type DataItem, and a second of type long (and the
reverse).


Several people have said this now, but the OPs code works fine in gcc
and at http://www.comeaucomputing.com/tryitout/.

Also, Dikumware's and SGI's documentation say that upper_bound only uses
pred(x, y) where x is the 3rd argument passed in and y is the elements
in the container.

What am I missing?

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