# C++ Programming/Code/Standard C Library/Functions/log

#### log edit

Syntax |
```
#include <cmath>
double log( double num );
``` |

The function log() returns the natural (base e) logarithm of *num*. There's a domain error if *num* is negative, a range error if *num* is zero.

In order to calculate the logarithm of x to an arbitrary base b, you can use:

```
double answer = log(x) / log(b);
```