C++ <list> - operator< Function

The C++ <list> operator< function is used to check whether the first list is less than the second list or not. It returns true if the first list is less than the second list, 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 lexicographically less than 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 the first list is less than the second list 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 {40, 50, 60};

  if (list1 < list2)
    cout<<"list1 is less than list2.\n";
  else
    cout<<"list1 is not less than list2.\n";

  if (list1 < list3)
    cout<<"list1 is less than list3.\n";
  else
    cout<<"list1 is not less than list3.\n";
    
  return 0;
}

The output of the above code will be:

list1 is not less than list2.
list1 is less than list3.