因為sort函式只能排序類似vector這樣的類，map是不能排序的。所以需要將map轉換為vector表示，那就需要pair

//map資料按照值來排序
void MapSortOfValue(vector<pair<int,string> >& vec,map<string,int>& m)
{
    for (map<string, int>::iterator it = m.begin(); it != m.end(); it++)
        vec.push_back(make_pair(it->second, it->first));
    sort(vec.begin(), vec.end());
}
 

sort預設按照first從小到大排序。

例子如下：

#include <iostream>
#include <vector>
#include <map>
#include <algorithm>
using namespace std;

//map資料按照值來排序
void MapSortOfValue(vector<pair<int,string> >& vec,map<string,int>& m)
{
    for (map<string, int>::iterator it = m.begin(); it != m.end(); it++)
        vec.push_back(make_pair(it->second, it->first));
    sort(vec.begin(), vec.end());
}

int
 
 main()
{
    vector<pair<int, string> > vec;
    map<string, int> m;
    m["ABC"] = 4;
    m["ACB"] = 2;
    m["CDB"] = 5;
    m["ADB"] = 1;

    cout << "排序前" << endl;
    for (map<string, int>::iterator it = m.begin(); it != m.end(); it++)
        cout << it->first.c_str() << " "
 
 << it->second << endl;
    cout << "---------------------" << endl;
    MapSortOfValue(vec, m);
    cout << "排序後" << endl;
    for (vector<pair<int, string> >::iterator it = vec.begin(); it != vec.end(); it++)
        cout << it->first << " " << it->second.c_str() << endl;
    return 0;
}

輸出結果如圖：