Re: performance of map in MSVC 10b2

I use map a lot in my daily work, so the performance of map is very
important to me. today i did a very simple test on MSVC10b2, using
std::map, std::unordered_map and boost::unordered_map, and found that
the test result is suprise to me.

here comes test code first:
MSVC10b2, WinXP
//-----------------------------------------------
#include <iostream>
#include <string>
#include <map>
#include <unordered_map>

#include <boost/unordered_map.hpp>
#include <boost/progress.hpp>

using namespace std;

int main()
{
        typedef std::unordered_map<int, string> map_t;
    //typedef boost::unordered_map<int, string> map_t;
        //typedef std::map<int, string> map_t;
        const int size = 1E7;
        map_t imap;
        {
                boost::progress_timer t1;
                boost::progress_display prog_bar(size);
                for(int i=0; i<size; ++i) {
                        imap[i] = "test";
                        ++prog_bar;
                }
        }
        {
                boost::progress_timer t2;
                string buff;
                for(int i=0; i<size; ++i) {
                        buff = imap[i];
                }
        }
        return 0;

}

//-----------------------------------------------------------

and the test result:

MAP INSERT FIND
std::map 7.73s 1.98s
boost::unorder_map 5.47s 0.80s
std::unorder_map 9.91s 2.98s

am i wrong with the usage? or something i didn't catch up here?