# log2() Function with Example in C++

C++ log2() function: Here, we are going to learn about the log2() function with example of cmath header in C++ programming language.
Submitted by IncludeHelp, on May 20, 2020

## C++ log2() function

log2() function is a library function of cmath header, it is used to get the binary logarithm (the base-2 logarithm) of the given value. It accepts a value (float, double, or long double) and returns the binary logarithm.

Syntax of log2() function:

C++11:

```     double log2 (double x);
float log2 (float x);
long double log2 (long double x);
double log2 (T x);
```

Parameter(s):

• x – represents the value whose binary logarithm to be found.

Return value:

It returns the binary logarithm of the given value x.

Note:

• If the given value is negative, it causes a domain error.
• If the given value is zero, it may cause a pole error.

Example:

```    Input:
float x = 2.0f

Function call:
log2(x);

Output:
1
```

### C++ code to demonstrate the example of log2() function

```// C++ code to demonstrate the example of
// log2() function

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

int main()
{
float x = 0.0f;

x = 10.0f;
cout << "log2(" << x << "): " << log2(x) << endl;

x = 2.0f;
cout << "log2(" << x << "): " << log2(x) << endl;

x = 20.0f;
cout << "log2(" << x << "): " << log2(x) << endl;

x = -10.4f;
cout << "log2(" << x << "): " << log2(x) << endl;

x = 0.0f;
cout << "log2(" << x << "): " << log2(x) << endl;

x = 100.6f;
cout << "log2(" << x << "): " << log2(x) << endl;

return 0;
}
```

Output

```log2(10): 3.32193
log2(2): 1
log2(20): 4.32193
log2(-10.4): nan
log2(0): -inf
log2(100.6): 6.65249
```

Reference: C++ log2() function