第四十五节 C++ STL（标准模板库）-映射类std::map std::multimap std::unordered_map std::unordered_multimap

map的操作与set类似，操作可参考上一节，这里仅介绍基本操作

映射类： 为key-value(键-值)对容器, 支持根据key查找value， 如根据int可查找对应的string

std::map: 存储唯一的键, 默认从小到大排序

std::mulitmap: 可存储重复的键 ， 默认从小到大排序

 std::unordered_map: 用散列函数排序，键唯一

 std::unordered_multimap：用散列函数排序，键可重复

#include     
#include 

use make_pair():
 [0] = first = 1, second = this is 1
 [1] = first = 2, second = this is 2
 [2] = first = 3, second = this is 3

use pair():
 [0] = first = 4, second = this is 4
 [1] = first = 5, second = this is 5
 [2] = first = 6, second = this is 6

map insert repetition key:
 [0] = first = 1, second = this is 1
 [1] = first = 2, second = this is 2
 [2] = first = 3, second = this is 3

multimap insert repetition key:
 [0] = first = 1, second = this is 1
 [1] = first = 2, second = this is 2
 [2] = first = 3, second = this is 3
 [3] = first = 3, second = 333333

read all key-value in multiset:
first = 3 second = this is 3
first = 3 second = this is 3