C++ <vector> - operator== Function

The C++ <vector> operator== function is used to check whether two vectors are equal or not. It returns true if two vectors are equal, else returns false. operator== checks the size of both vectors, if sizes are same then it compares elements of vectors sequentially and stops comparison after first mismatch.

Syntax

• C++98
• C++11

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

template <class T, class Alloc>
bool operator== (const vector<T,Alloc>& lhs, const vector<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, operator== function is used to check whether two vectors are equal or not.

#include <iostream>
#include <vector>
using namespace std;
 
int main (){
  vector<int> vec1 {10, 20, 30};
  vector<int> vec2 {10, 20, 30};
  vector<int> vec3 {10, 20};

  if (vec1 == vec2)
    cout<<"vec1 and vec2 are equal.\n";
  else
    cout<<"vec1 and vec2 are not equal.\n";

  if (vec1 == vec3)
    cout<<"vec1 and vec3 are equal.\n";
  else
    cout<<"vec1 and vec3 are not equal.\n";
    
  return 0;
}

The output of the above code will be:

vec1 and vec2 are equal.
vec1 and vec3 are not equal.