C++ <list> - operator== Function

The C++ <list> operator== function is used to check whether two lists are equal or not. It returns true if two lists are equal, else returns false. operator== compares elements of lists sequentially and stops comparison after first mismatch.

Syntax

• C++98
• C++11

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

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

Parameters

Return Value

Returns true if the contents of lhs are equal to the contents of rhs, else returns false.

Time Complexity

Linear i.e, Θ(n).

Example:

In the example below, the operator== function is used to check whether two lists are equal or not.

#include <iostream>
#include <list>
using namespace std;
 
int main (){
  list<int> list1 {10, 20, 30};
  list<int> list2 {10, 20, 30};
  list<int> list3 {10, 20};

  if (list1 == list2)
    cout<<"list1 and list2 are equal.\n";
  else
    cout<<"list1 and list2 are not equal.\n";

  if (list1 == list3)
    cout<<"list1 and list3 are equal.\n";
  else
    cout<<"list1 and list3 are not equal.\n";
    
  return 0;
}

The output of the above code will be:

list1 and list2 are equal.
list1 and list3 are not equal.