C++基础：STL之map

绝地灬酷狼 2022-12-18 03:59 175阅读 0赞

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这篇文章介绍一下STL中map的基本使用方法。

### 目录 ###

*  map
 *  头文件和命名空间
 *  常用的成员函数
 *  代码使用示例
 *  示例执行结果
 *  总结

--------------------

# map #

> 使用场景：map能实现很多内容，可能实际想的最多的就是key-value映射的数据类型，按key取值是实际的使用示例。

# 头文件和命名空间 #

> \#include <map>  
> using namespace std;

# 常用的成员函数 #

<table> 
 <thead> 
  <tr> 
   <th>函数名</th> 
   <th>用途</th> 
   <th>功能说明</th> 
  </tr> 
 </thead> 
 <tbody> 
  <tr> 
   <td>size()</td> 
   <td>查询遍历</td> 
   <td>获取元素个数</td> 
  </tr> 
  <tr> 
   <td>begin()</td> 
   <td>查询遍历</td> 
   <td>获取指向第一个元素的迭代器(正序)</td> 
  </tr> 
  <tr> 
   <td>end()</td> 
   <td>查询遍历</td> 
   <td>获取末尾的迭代器(正序)</td> 
  </tr> 
  <tr> 
   <td>rbegin()</td> 
   <td>查询遍历</td> 
   <td>获取指向第一个元素的迭代器(逆序)</td> 
  </tr> 
  <tr> 
   <td>rend()</td> 
   <td>查询遍历</td> 
   <td>获取末尾的迭代器(逆序)</td> 
  </tr> 
  <tr> 
   <td>empty()</td> 
   <td>查询遍历</td> 
   <td>确认map是否为空</td> 
  </tr> 
  <tr> 
   <td>find(x)</td> 
   <td>查询遍历</td> 
   <td>查找一个key为x的元素，返回相应的迭代器的位置</td> 
  </tr> 
  <tr> 
   <td>insert(x)</td> 
   <td>插入</td> 
   <td>插入数据x</td> 
  </tr> 
  <tr> 
   <td>erase(x)</td> 
   <td>删除</td> 
   <td>删除指定元素x</td> 
  </tr> 
  <tr> 
   <td>clear()</td> 
   <td>删除</td> 
   <td>删除所有元素</td> 
  </tr> 
 </tbody> 
</table>

--------------------

# 代码使用示例 #

#include <iostream>
    #include <map>
    using namespace std;
    
    int check_map_insert(pair<map<int,string>::iterator, bool> p) {
        if (p.second) {
            cout << "Insert Success. " << endl; return 1;
        } else {
            cout << "Insert Failed." << endl; return 0;
        }
    }
    
    int main() {
        map <int, string> m;
    
        cout << "Size of map m : " << m.size() << endl;
        pair<map<int, string>::iterator, bool> p;
        p = m.insert(pair<int,string>(1001,"LiuMiao"));
        check_map_insert(p);
        p = m.insert(make_pair<int,string>(1003,"LiuMiaoCN"));
        check_map_insert(p);
        p = m.insert(pair<int,string>(1001,"LiuMiao"));
        check_map_insert(p);
        p = m.insert(map<int,string>::value_type (1002,"Michael"));
        check_map_insert(p);
        cout << "Size of map m : " << m.size() << endl;
    
        for (int i=1001; i < 1001+m.size(); i++) cout << m[i] <<endl;
    
        map <int,string>::iterator it = m.begin();
        cout << "begin(): [" << it->first <<" , " << it->second << "]" << endl;
        it = m.end();
        cout << "begin(): [" << it->first <<" , " << it->second << "]" << endl;
        it--;
        cout << "begin(): [" << it->first <<" , " << it->second << "]" << endl;
    
        for (it=m.begin(); it != m.end(); it++) cout << "[ " << it->first << " , " << it->second << "]" << endl;
    
        map <int,string>::reverse_iterator rit;
        for (rit=m.rbegin(); rit != m.rend(); rit++) cout << "[ " << rit->first << " , " << rit->second << "]" << endl;
    
        it = m.find(1002);
        if (it != m.end()) {
            cout << "Founded: " << "[ " << it->first << " , " << it->second << "]" << endl;
        } else {
            cout << "key 1002: Not Founded. " << endl;
        }
    
        it = m.find(1002);
        m.erase(it);
    
        for (it=m.begin(); it != m.end(); it++) cout << "[ " << it->first << " , " << it->second << "]" << endl;
    
        it = m.find(1002);
        if (it != m.end()) {
            cout << "Founded: " << "[ " << it->first << " , " << it->second << "]" << endl;
        } else {
            cout << "key 1002: Not Founded. " << endl;
        }
    
    }

# 示例执行结果 #

Size of map m : 0
    Insert Success. 
    Insert Success. 
    Insert Failed.
    Insert Success. 
    Size of map m : 3
    LiuMiao
    Michael
    LiuMiaoCN
    begin(): [1001 , LiuMiao]
    begin(): [1750469833 , ]
    begin(): [1003 , LiuMiaoCN]
    [ 1001 , LiuMiao]
    [ 1002 , Michael]
    [ 1003 , LiuMiaoCN]
    [ 1003 , LiuMiaoCN]
    [ 1002 , Michael]
    [ 1001 , LiuMiao]
    Founded: [ 1002 , Michael]
    [ 1001 , LiuMiao]
    [ 1003 , LiuMiaoCN]
    key 1002: Not Founded.

# 总结 #

变长支持、泛化类型、常用功能函数内嵌、可以使用其他多种STL的函数、使用简单，而实际上通过key获取相应的value的需求非常广泛，这才是map被使用的更重要的原因，而map还可以继续有细化其他的使用类型，在后续的文章中将进一步展开。

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