Re: Providing a no-overhead way for a contained class to access its container?

From:
PeteOlcott <PeteOlcott@gmail.com>
Newsgroups:
comp.lang.c++
Date:
Tue, 17 Jun 2008 05:30:13 -0700 (PDT)
Message-ID:
<293706b4-cbee-4cc0-bbe2-0b2c6ba42191@z72g2000hsb.googlegroups.com>
On Jun 17, 1:00 am, Jerry Coffin <jcof...@taeus.com> wrote:

In article <5dd80816-49c4-442d-a25c-076b6c260305
@y21g2000hsf.googlegroups.com>, PeteOlc...@gmail.com says...

[ ... ]

The only reason that I even need to have the contained class is so
that I can overload the operator<() on it, and thus use std::sort().


You can use std::sort without having an overloaded operator< for the
type. You can create the comparison as either a function or a functor,
and then pass it as the third parameter to std::sort. For example:

#include <vector>
#include <algorithm>
#include <iostream>

class X {
        int y;
public:
        X(int a=0) : y(a) {}
        operator int() const { return y; }

};

struct less {
        bool operator()(X const &a, X const &b) {
                return (int)a < (int)b;
        }

};

int main() {
        std::vector<X> x;

        for (int i=0; i<20; i++)
                x.push_back(rand());

        std::sort(x.begin(), x.end(), less());
        std::copy(x.begin(), x.end(),
                std::ostream_iterator<int>(std::cout, "\n"=

));

        return 0;

}

--
    Later,
    Jerry.

The universe is a figment of its own imagination.


What about the case where the contained class must store its data in
its container?

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