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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是否小于其他multimap。

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multimap对象的右侧，则返回true，否则返回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:

链接：https://www.learnfk.comhttps://www.learnfk.com/c++/cpp-multimap-non-member-operator<-function.html

来源：LearnFk无涯教程网

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;  
  
   m2.emplace('a', 10);  
  
   if (m1 < m2)  
      cout << "Multimap m1 is less than m2." << endl;  
  
   m1 = m2;  
  
   if (!(m1 < m2))  
      cout << "Multimap m1 is not less than m2." << endl;  
  
   return 0;  
}

输出:

Multimap m1 is less than m2.
Multimap m1 is not less than m2.

在上面的示例中，有两个multimapm1和m2。 m2包含一个元素，而m1为空。当我们比较两个multimap时，它将显示消息"multimapm1小于m2"，将m2分配给m1后，两个multimap具有相等的元素，则它将显示消息"multimapm1不小于m2"。

无涯教程网

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;    
   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));    
   }    
    
   if (m1 <m2)    
      cout << "The multimap m1 is less than the multimap m2." << endl;    
   else    
      cout << "The multimap m1 is not less than the multimap m2." << endl;    
    
   if (m1 <m3)    
      cout << "The multimap m1 is less than the multimap m3." << endl;    
   else    
      cout << "The multimap m1 is not less than the multimap m3." << endl;    
}

输出:

The multimap m1 is less than the multimap m2.
The multimap m1 is not less than the multimap m3.

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 <multimap>  
  
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;  
  
  m2.insert(make_pair('d',40));  
  
  cout << (m1 < m2) << endl;  
  
  return 0;  
}

输出:

0
1

在上面的示例中，如果m1小于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 (m1 < m2)    
  
        cout << "\nIncorrect ID or Password..." << endl;   
   
   else    
        cout << "\nWelcome to your Page..." << 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m1是否小于m2。如果m1的ID和密码不少于m2，则登录成功，否则登录失败。

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