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C++ Multimap 中的 operator函数

C++ 运算符是Multimap的非成员重载函数。此函数用于检查第一个multimap是否小于或等于其他。

operator - 语法

template <class Key, class T, class Compare, class Alloc>  
  bool operator<= ( const multimap<Key,T,Compare,Alloc>& lhs,  
                    const multimap<Key,T,Compare,Alloc>& rhs );

operator - 参数

lhs :第一个multimap对象。

rhs :第二个multimap对象。

operator - 返回值

如果multimap对象的左侧小于或等于multimap对象的右侧，则返回 true ，否则为 false 。

operator - 例子1

让我们看一个简单的示例，检查第一个multimap是否小于或等于:

在线运行复制代码

#include <iostream>  
#include <map>  
  
using namespace std;  
  
int main() {  
   multimap<char, int> m1;  
   multimap<char, int> m2;  
  
   m1.emplace('a', 1);  
   m2.emplace('a', 1);  
  
   if (m1 <= m2)  
      cout << "Multimap m1 is less than or equal to m2." << endl;  
  
   m1.emplace('b', 2);  
  
   if (!(m1 <= m2))  
      cout << "Multimap m1 is not less than or equal to m2." << endl;  
  
   return 0;  
}

输出:

Multimap m1 is less than or equal to m2.
Multimap m1 is not less than or equal to m2.

在上面的示例中，有两个multimapm1和m2。 m1和m2包含一个元素。当我们比较两个multimap时，它将显示消息"multimapm1小于或等于m2"，并且在m1中添加一个额外的元素后，它将显示消息"multimapm1不小于或等于m2"。

operator - 例子2

让我们看一个简单的例子:

复制代码

#include <map>    
#include <iostream>    
    
int main ()    
{    
   using namespace std;    
   multimap <int, int> m1, m2, m3, m4;    
   int i;    
   typedef pair <int, int> Int_Pair;    
    
   for (i = 1; i <3; i ++)    
   {    
      m1.insert (Int_Pair (i, i));    
      m2.insert (Int_Pair (i, i * i));    
      m3.insert (Int_Pair (i, i - 1));    
      m4.insert (Int_Pair (i, i));    
   }    
    
   if (m1 <= m2)    
      cout << "The multimap m1 is less than or equal to the multimap m2." << endl;    
   else    
      cout << "The multimap m1 is greater than the multimap m2." << endl;    
    
   if (m1 <= m3)    
      cout << "The multimap m1 is less than or equal to the multimap m3." << endl;    
   else    
      cout << "The multimap m1 is greater than the multimap m3." << endl;    
    
   if (m1 <= m4)    
      cout << "The multimap m1 is less than or equal to the multimap m4." << endl;    
   else    
      cout << "The multimap m1 is greater than the multimap m4." << endl;    
}

输出:

The multimap m1 is less than or equal to the multimap m2.
The multimap m1 is greater than the multimap m3.
The multimap m1 is less than or equal to the multimap m4.

operator - 例子3

让我们看一个简单的例子:

在线运行复制代码

#include <iostream>  
#include <map>  
  
using namespace std;  
  
int main()  
{  
  multimap<char,int> m1, m2;  
    
  m1.insert(make_pair('a',10));  
  m1.insert(make_pair('b',20));  
  m1.insert(make_pair('c',30));  
    
  m2 = m1;  
      
  cout << (m1 <= m2) << endl;  
  
  m1.insert(make_pair('d',40));  
  
  cout << (m1 <= m2) << endl;  
  
  return 0;  
}

输出:

1
0

在上面的示例中，如果m1小于或等于m2，则它将返回1，否则返回0。

operator - 例子4

复制代码

#include <map>    
#include <iostream>    
using namespace std;   
    
int main ()    
{    
   multimap<int,string> m2;  
   typedef multimap<int,string> login;   
     
   m2.insert({2040, "xyz@123"}); //stored id and password  
     
   string password;  
   int id;  
   login m1;  
     
       cout<<"---------Login----------"<<endl<<endl;  
       cout<<"Enter the ID and password: \n";  
       cin>> id;             //Get key  
       cin>> password;      //Get value  
       m1.insert({id, password});  //Put them in multimap  
  
     cout<<"ID and password you have entered: \n";  
     for (auto it = m1.begin(); it != m1.end(); it++) {  
        cout << (*it).first << "    " << (*it).second << endl;  
      }  
      cout<<"ID and Password stored in the system :\n";  
     for (auto it = m2.begin(); it != m2.end(); it++) {  
        cout << (*it).first << "    " << (*it).second << endl;  
     }  
  
    
   if (m2 <= m1)    
        cout << "\nWelcome to your Page..." << endl;   
   else    
        cout << "\nIncorrect ID or Password..." << endl;   
        
      return 0;  
}

输出:

1).
---------Login----------

Enter the ID and password: 
1020     xyz
ID and password you have entered: 
1020     xyz
ID and Password stored in the system:
2040     xyz@123

Incorrect ID or Password...


2).
---------Login----------

Enter the ID and password: 
2040     xyz@123
ID and password you have entered: 
2040     xyz@123
ID and Password stored in the system:
2040     xyz@123

Welcome to your Page...

在上面的示例中，有两个multimapm1和m2。 m1包含存储的ID和密码，第二个multimapm2存储用户输入的ID和密码。它检查m2是否小于或等于m1。如果m2的ID和密码小于或等于m1，则登录成功，否则登录失败。

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