template<
	class Key,
	class T,
	class Compare=std::less<Key>,
	class Allocator=std::allocator<std::pair<const Key,T>>
>class map;

键值对会根据键来用 Compare 排序，具体到 std::map<int, int> 就是：

map<int,int,std::less<int>>

一、迭代器 iterator

for(map<int,int>::iterator it=mp.begin();it!=mp.end();++it)
	cout<<it->first<<"--"<<it->second<<"	";

for(map<int,int>::const_iterator it=mp.begin();it!=mp.end();++it)
	cout<<it->first<<"--"<<it->second<<"	";

二、类型萃取 (traits) value_type

for(map<int,int>::value_type& i:mp)
	cout<<i.first<<"--"<<i.second<<"	";

三、实际类型 pair

for(pair<const int ,int>&i:mp)//key必须是const的
	cout<<i.first<<"--"<<i.second<<"	";

四、结构化绑定 auto

for(auto&[k,v]:mp)
    cout<<k<<"--"<<v<<"	";

五、测试代码如下：

#include<iostream>
#include<thread>
#include<atomic>
#include<unordered_map>
#include<map>
using namespace std;

int main(){
          
   

    map<int,int>mp;
    for(int i=0;i<10;i++)mp[i]=i;

    cout<<endl<<"iterator:"<<endl;
    for(map<int,int>::iterator it=mp.begin();it!=mp.end();++it)
        cout<<it->first<<"--"<<it->second<<"	";

    cout<<endl<<"const iterator:"<<endl;
    for(map<int,int>::const_iterator it=mp.begin();it!=mp.end();++it)
        cout<<it->first<<"--"<<it->second<<"	";

    cout<<endl<<"value_type :"<<endl;
    for(map<int,int>::value_type& i:mp)
        cout<<i.first<<"--"<<i.second<<"	";

    cout<<endl<<"pair:"<<endl;
    for(pair<const int ,int>&i:mp)
        cout<<i.first<<"--"<<i.second<<"	";

    cout<<endl<<"auto:"<<endl;
    for(auto&[k,v]:mp)
    cout<<k<<"--"<<v<<"	";

    getchar();
    return 0;
}

六、map遍历结果：