log2() function in C++ with Examples (original) (raw)

Last Updated : 12 Jul, 2025

The function log2() of cmath header file in C++ is used to find the logarithmic value with base 2 of the passed argument. Syntax:

log2(x)

Parameters: This function takes a value x, in the range [0, ∞] whose log value is to be found.Return Type: It returns the logarithmic value, as double, float or long double type, based on the following conditions:

If x > 1: It returns the positive logarithmic value of x.
If x is equals to 1: It returns 0.
If 0 < x < 1: It returns the negative logarithmic value of x.
If x is equals to 0: It returns the negative infinity(-∞).
If x < 0: It returns NaN(Not a Number).

Below examples demonstrate the use of log2() method:Example 1:

CPP `

// C++ program to illustrate log2() function

#include <bits/stdc++.h> using namespace std;

// Driver Code int main() { long b = 16; float c = 2.5; double d = 10.35; long double e = 25.5;

// Logarithmic value of long datatype
cout << log2(b) << "\n";

// Logarithmic value of float datatype
cout << log2(c) << "\n";

// Logarithmic value of double datatype
cout << log2(d) << "\n";

// Logarithmic value of long double datatype
cout << log2(e) << "\n";

return 0;

}

Output:

4 1.32193 3.37156 4.67243

Example 2:

CPP `

// C++ program to illustrate log2() function

#include <bits/stdc++.h> using namespace std;

// Driver Code int main() { // To show extreme cases int a = 0; int b = -16;

// Logarithmic value of 0
cout << log2(a) << "\n";

// Logarithmic value of negative value
cout << log2(b) << "\n";

return 0;

}