C++基础：STL之可重复集合multiset

今天药忘吃喽~ 2022-12-18 05:51 182阅读 0赞

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这篇文章介绍一下STL中multiset的基本使用方法。

### 目录 ###

*  set
 *  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

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

# set #

> 使用场景：set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，set和map的最大区别在于是否能够有重复。

# 头文件和命名空间 #

> \#include <set>  
> 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x，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 <set>
    using namespace std;
    
    int check_after_insert(string str,multiset<string> s) {
        if (s.find(str) != s.end()) {
            cout << "Insert Success. " << endl; return 1;
        } else {
            cout << "Insert Failed." << endl; return 0;
        }
    }
    
    int main() {
        multiset <string> s;
    
        cout << "Size of map s : " << s.size() << endl;
        s.insert("LiuMiao");
        check_after_insert("LiuMiao",s);
        s.insert("LiuMiaoCN");
        check_after_insert("LiuMiaoCN",s);
        s.insert("Michael");
        check_after_insert("Michael",s);
        s.insert("LiuMiaoCN");
        check_after_insert("LiuMiaoCN",s);
        cout << "Size of set s : " << s.size() << endl;
    
        multiset <string>::iterator it = s.begin();
        cout << "begin(): [" << *it << "]" << endl;
        it = s.end();
        //cout << "begin(): [" << *it << "]" << endl;
        it--;
        cout << "begin(): [" << *it << "]" << endl;
    
        for (it=s.begin(); it != s.end(); it++) cout << "[ " << *it << "]" << endl;
    
        multiset <string>::reverse_iterator rit;
        for (rit=s.rbegin(); rit != s.rend(); rit++) cout << "[ " << *rit << "]" << endl;
    
        it = s.find("LiuMiao");
        if (it != s.end()) {
            cout << "Founded: " << "[ " << *it << "]" << endl;
        } else {
            cout << "LiuMiao: Not Founded. " << endl;
        }
    
        it = s.find("LiuMiao");
        s.erase(it);
    
        for (rit=s.rbegin(); rit != s.rend(); rit++) cout << "[ " << *rit << "]" << endl;
    
        it = s.find("LiuMiao");
        if (it != s.end()) {
            cout << "Founded: " << "[ " << *it << "]" << endl;
        } else {
            cout << "LiuMiao: Not Founded. " << endl;
        }
    }

# 示例执行结果 #

Size of map s : 0
    Insert Success. 
    Insert Success. 
    Insert Success. 
    Insert Success. 
    Size of set s : 4
    begin(): [LiuMiao]
    begin(): [Michael]
    [ LiuMiao]
    [ LiuMiaoCN]
    [ LiuMiaoCN]
    [ Michael]
    [ Michael]
    [ LiuMiaoCN]
    [ LiuMiaoCN]
    [ LiuMiao]
    Founded: [ LiuMiao]
    [ Michael]
    [ LiuMiaoCN]
    [ LiuMiaoCN]
    LiuMiao: 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，结合其他类型进行泛化，使用非常广泛，与set相比主要的特点在于可重复，本文示例代码和set除了将定义从set修改为multiset之外，其余完全不变，使用方法一致。

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