[C++知识库]C++笔记之std::map容器_demo_示例

链接：?C++中的std::map容器

链接是概念介绍和简单用法笔记，下面是一个比较全的代码。

#include <iostream>
#include <string>
#include <map>

using namespace std;

void fun_map()
{
    std::map<std::string,int> map_data1 = {
        {"000",0},
        {"aaa",0},
        {"bbb",0}
    };
    map_data1.at("aaa") = 1;
    map_data1.at("bbb") = 2;
    // map_data1.at("zzz") = 2; //error 初始化中没有的不可用at赋值
    map_data1["ccc"] = 3;
    map_data1["ddd"] = 4;
    map_data1.insert(std::pair<std::string,int>("zzz",5));
    map_data1.insert(std::pair<std::string,int>("fff",6));

    for(auto& data: map_data1){
        std::cout << data.first << " is: " << data.second << std::endl;
    }
    // 打印结果
    // 000 is: 0
    // aaa is: 1
    // bbb is: 2
    // ccc is: 3
    // ddd is: 4
    // fff is: 6 //注意：这里打印与插入顺序不一致，因为map是自动排序的
    // zzz is: 5

    std::cout << "[iterator output] ";
    //for(std::map<std::string,int>::iterator it = map_data1.begin();it != map_data1.end();++it){
    for(auto it = map_data1.begin();it != map_data1.end();++it){
        std::cout << it->first << " is: " << it->second << "    ";
    }
    std::cout << '\n' << std::endl;
    // 打印结果 
    // [iterator output] 000 is: 0    aaa is: 1    bbb is: 2    ccc is: 3    ddd is: 4    fff is: 6    zzz is: 5 

    std::cout << "size: " << map_data1.size() << "    empty[true or flase]: " << map_data1.empty() ;
    map_data1.clear();
    std::cout << " => clear() => size: " << map_data1.size() << "    empty[true or flase]: " << map_data1.empty() << std::endl;
    // 打印结果
    // size: 7    empty[true or flase]: 0 => clear() => size: 0    empty[true or flase]: 1
    
    map_data1["AA"] = 11;
    map_data1["BB"] = 22;
    map_data1["CC"] = 33;
    map_data1["DD"] = 44;

    for(auto& data: map_data1){
        std::cout << data.first << " is: " << data.second << "    " << std::endl;
    }
    // 打印结果
    // AA is: 11    
    // BB is: 22    
    // CC is: 33    
    // DD is: 44 

    auto it = map_data1.find("BB");
    if (it != map_data1.end()){
        map_data1.erase(it);
    }else{
        std::cout << "没有找到" << std::endl;
    }
    // map_data1.erase(map_data1.begin(),map_data1.end()); //删除所有；等同于clear()

    map_data1.erase("DD");

    for(auto& data: map_data1){
        std::cout << data.first << " is: " << data.second << "    ";
    }
    std::cout << '\n' << std::endl;
    // 打印结果
    // AA is: 11    CC is: 33 

}