template<    class T1,    class T2> struct pair;

1.定义（构造）：     pair<int, double> p1;          //使用默认构造函数     pair<int, double> p2(1, 2.4);  //用给定值初始化     pair<int, double> p3(p2);      //拷贝构造函数2.访问两个元素（通过first和second）：     pair<int, double> p1;          //使用默认构造函数     p1.first = 1;     p1.second = 2.5;     cout << p1.first << " " << p1.second << endl;

template< class T1, class T2 >std::pair<T1,T2> make_pair( T1 t, T2 u );template< class T1, class T2 >std::pair<V1,V2> make_pair( T1&& t, T2&& u );

#include <iostream>#include <utility>#include <functional> int main(){    int n = 1;    int a[5] = {1,2,3,4,5};     // build a pair from two ints    auto p1 = std::make_pair(n, a[1]);    std::cout << "The value of p1 is "              << "(" << p1.first << ", " << p1.second << ")\n";     // build a pair from a reference to int and an array (decayed to pointer)    auto p2 = std::make_pair(std::ref(n), a);    n = 7;    std::cout << "The value of p2 is "              << "(" << p2.first << ", " << *(p2.second+1) << ")\n";}//The value of p1 is (1, 2)//The value of p2 is (7, 2)

#include<iostream>#include<utility>#include<string>using namespace std;int main (){    pair<string, double>product1 ("tomatoes", 3.25);    pair<string, double>product2;    pair<string, double>product3;    product2.first = "lightbulbs"; // type of first is string    product2.second = 0.99;        // type of second is double    product3 = make_pair ("shoes", 20.0);    cout << "The price of " << product1.first << " is $" << product1.second << "\n";    cout << "The price of " << product2.first << " is $" << product2.second << "\n";    cout << "The price of " << product3.first << " is $" << product3.second << "\n";    return 0;}//The price of tomatoes is $3.25//The price of lightbulbs is $0.99//The price of shoes is $20