In this C++ tutorial, you will learn how to find base-2 logarithm of given number using log2() function of cmath, with syntax and examples.

C++ log2()

C++ log2() returns base-2 logarithm of given number (argument).

Syntax

The syntax of C++ log2() is

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log2(x)

where

ParameterDescription
xA double, float, long double, or any integral type value.

Returns

The return value depends on the type of value passed for parameter x.

The return value of log2(x) is

  • double if x is double or integral type.
  • float if x is float.
  • long double if x is long double.

The synopsis of log2() function is

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double log2 (double x);
float log2 (float x);
long double log2 (long double x);
double log2 (T x); // for integral type argument values

log2() is a function of cmath library. Include cmath library at the start of program, if using log2() function.

Example

In this example, we read a value from user into variable x, and find its base-2 logarithm value using log2() function.

C++ Program

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#include <iostream>
#include<cmath>
using namespace std;

int main() {
    double x;
    cout << "Enter a number : ";
    cin >> x;
    
    double result = log2(x);
    cout << "log2(" << x << ") : " << result << endl;
}

Output

Enter a number : 16
log2(16) : 4
Program ended with exit code: 0
Enter a number : 1
log2(1) : 0
Program ended with exit code: 0
Enter a number : -5
log2(-5) : nan
Program ended with exit code: 0

Conclusion

In this C++ Tutorial, we learned the syntax of C++ log2(), and how to use this function to find base-2 logarithm of given number, with the help of examples.