STLmap container size and swap

STLmap container size and swap

Function description:
*
Statistics of map container size and exchange

Function prototype:

size();       //返回容器中元素的数目
empty();      //判断容器是否为空
swap(st);     //交换两个集合容器

Code example:

#include<iostream>
#include<map>
using namespace std;
void printMap(map<int, int>&m)
{
    
    
       for (map<int, int>::iterator it = m.begin(); it != m.end(); it++)
       {
    
    
              cout << "key=" << it->first << " value=" << it->second << endl;
       }
       cout << endl;
}
//大小
void test01()
{
    
    
       map<int, int>m;
       m.insert(pair<int, int >(1, 10));
       m.insert(pair<int, int >(2, 20));
       m.insert(pair<int, int >(3, 30));
       if (m.empty())
       {
    
    
              cout << "m为空" << endl;
       }
       else
       {
    
    
              cout << "m不为空" << endl;
              cout << "m的大小为：" << m.size() << endl;
       }
}
//交换
void test02()
{
    
    
       map<int, int>m;
       m.insert(pair<int, int >(1, 10));
       m.insert(pair<int, int >(2, 20));
       m.insert(pair<int, int >(3, 30));
       map<int, int>m2;
       m2.insert(pair<int, int >(5, 100));
       m2.insert(pair<int, int >(6, 200));
       m2.insert(pair<int, int >(7, 300));
       cout << "交换前：" << endl;
       printMap(m);
       printMap(m2);
       m.swap(m2);
       cout << "交换后：" << endl;
       printMap(m);
       printMap(m2);
}
int main()
{
    
    
       //test01();
       test02();
       system("pause");
       return 0;
}

to sum up:

Statistics size --size

Determine whether it is empty—empty

Exchange container--swap