[boost] Feed pointers to a container, however use the member of the data type which pointer refer to

Subject: [boost] Feed pointers to a container, however use the member of the data type which pointer refer to
From: è·¯ é‚“ (denglu36_at_[hidden])
Date: 2009-09-21 22:32:25

Dear All:

In the following codes, I feed the container with B*, however I user the member of  B as the index. Can somebody explain to me how this work out?  And It  seems that if smart pointers are feeded into the container, it still works out. 

#include <boost/config.hpp> /* keep it first to prevent nasty warns in MSVC */
#include <boost/multi_index_container.hpp>
#include <boost/multi_index/ordered_index.hpp>
#include <boost/multi_index/member.hpp>
#include <iostream>

using namespace boost::multi_index;

class B
{
public:
    int idx;
};

typedef boost::multi_index_container<
    B*,
    indexed_by<
        ordered_unique<
            BOOST_MULTI_INDEX_MEMBER(B, int, idx)
        >
    >
>Container;

int main()
{
    Container container;
    B* p1 = new B;
    B* p2 = new B;
    p1->idx = 2;
    p2->idx = 1;
    container.insert(p1);
    container.insert(p2);
    Container::iterator iter;
    for(iter=container.begin();iter!=container.end();iter++)
    {
        B* tmp = (*iter);
        std::cout << tmp->idx << std::endl;
    }
    return 0;
}