C++ operator == 是Multimap的非成员重载函数。此函数用于检查两个multimap是否相等。
Note: multimap对象之间的比较取决于元素的成对比较。如果两个映射具有相同数量的元素并且其对应元素具有相同的值，则它们是相等的。否则，它们是不相等的。
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对象的左侧等于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，检查两个multimap是否相等:
#include <iostream>
#include <map>
using namespace std;
int main() {
multimap<char, int> m1;
multimap<char, int> m2;
if (m1 == m2)
cout << "Both multimaps are equal." << endl;
m1.emplace(a, 10);
//after adding element in multimap m1
if (!(m1 == m2))
cout << "Both multimaps are not equal." << endl;
return 0;
}
输出:
Both multimaps are equal. Both multimaps are not equal.
在上面的示例中，multimapm1和m2为空。因此，operator ==将返回true，并且在multimapm1中添加一个元素后，m1的大小变得与m2的大小不同。因此，它将返回false。
operator== - 例子2
让我们看一个简单的例子:
#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 = 0; i <3; i ++)
{
m1.insert (Int_Pair (i, i));
m2.insert (Int_Pair (i, i * i));
m3.insert (Int_Pair (i, i));
}
if (m1 == m2)
cout << "The multimaps m1 and m2 are equal." << endl;
else
cout << "The multimaps m1 and m2 are not equal." << endl;
if (m1 == m3)
cout << "The multimaps m1 and m3 are equal." << endl;
else
cout << "The multimaps m1 and m3 are not equal." << endl;
return 0;
}
输出:
The multimaps m1 and m2 are not equal. The multimaps m1 and m3 are equal.
operator== - 例子3
让我们看一个简单的例子:
#include <iostream>
#include <map>
using namespace std;
int main ()
{
multimap < int , char > m1 ;
m1 . insert ( make_pair ( 1 , a ));
auto m2 = m1 ;
cout << ( m1 == m2 ) << endl ;
m2 . insert ( make_pair ( 1 , b ));
m2 . insert ( make_pair ( 2 , c ));
cout << ( m1 == m2 ) << endl ;
return 0 ;
}
输出:
1 0
在上面的示例中，如果m1和m2相等，则它将返回1，否则返回0。
operator== - 例子4
#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 << "\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。它检查两个multimap是否具有相同的元素。如果ID和密码匹配，则登录成功，否则登录失败。
