The std::less is a member of the functional class (<functional.h>) used for performing comparisons. It is defined as a function object class for less than inequality comparison which returns a boolean value depending upon the condition. This can be used to change the functionality of the given function. It can be used with various standard algorithms like sort, lower_bound etc.
Header File:
#include <functional.h>
Template Class:
template <class T> struct less { // Declaration of the less operation bool operator() (const T& x, const T& y) const { return x < y; } // Type of first parameter typedef T first_argument_type; // Type of second parameter typedef T second_argument_type; // The result is returned // as bool type typedef bool result_type; };
Syntax:
std::less()
Parameter: This function accepts the type of the arguments T, as the parameter, to be compared by the functional call.
Return Type: It return a boolean value depending upon condition(let a & b are 2 element):
- True: If a is less than b.
- False: If a is greater than b.
Time Complexity: O(1)
Auxiliary Space: O(1)
Below is the illustration of std::less in C++:
Program 1:
// C++ program to illustrate // std::less function #include <algorithm> #include <functional> #include <iostream> using namespace std;
// Function to print array arr[] void printArray( int arr[], int N)
{ for ( int i = 0; i < N; i++) {
cout << arr[i] << ' ' ;
}
} // Driver Code int main()
{ int arr[] = { 26, 23, 21, 22,
28, 27, 25, 24 };
int N = sizeof (arr) / sizeof (arr[0]);
// Sort the array in increasing order
sort(arr, arr + N, less< int >());
// Print sorted array
printArray(arr, N);
return 0;
} |
21 22 23 24 25 26 27 28
Program 2:
// C++ program to illustrate less #include <iostream> #include <algorithm> #include <functional> using namespace std;
// Template template < typename A, typename B,
typename U = std::less< int > >
// Function to check if a < b or not bool f(A a, B b, U u = U())
{ return u(a, b);
} // Driver Code int main()
{ int X = 1, Y = 2;
// If X is less than Y or not
cout << std::boolalpha;
cout << f(X, Y) << '\n' ;
X = 2, Y = -1;
// If X is less than Y or not
cout << f(X, Y) << '\n' ;
return 0;
} |
true false
Reference: http://www.cplusplus.com/reference/functional/less/