function
<cmath> <ctgmath>

# log

```double log (double x);
```
```     double log  (     double x);
float logf (      float x);
long double logl (long double x);
```
```     double log (     double x);
float log (      float x);
long double log (long double x);
```
```     double log (double x);
float log (float x);
long double log (long double x);
double log (T x);           // additional overloads for integral types```
Compute natural logarithm
Returns the natural logarithm of x.

The natural logarithm is the base-e logarithm: the inverse of the natural exponential function (exp). For common (base-10) logarithms, see log10.

Header <tgmath.h> provides a type-generic macro version of this function.
This function is overloaded in `<complex>` and `<valarray>` (see complex log and valarray log).
Additional overloads are provided in this header (`<cmath>`) for the integral types: These overloads effectively cast x to a `double` before calculations.

This function is also overloaded in `<complex>` and `<valarray>` (see complex log and valarray log).

### Parameters

x
Value whose logarithm is calculated.
If the argument is negative, a domain error occurs.

### Return Value

Natural logarithm of x.
If x is negative, it causes a domain error.
If x is zero, it may cause a pole error (depending on the library implementation).

If a domain error occurs, the global variable errno is set to EDOM.
If a pole error occurs, the global variable errno is set ERANGE.
If a domain error occurs:
- And math_errhandling has MATH_ERRNO set: the global variable errno is set to EDOM.
- And math_errhandling has MATH_ERREXCEPT set: FE_INVALID is raised.

If a pole error occurs:
- And math_errhandling has MATH_ERRNO set: the global variable errno is set to ERANGE.
- And math_errhandling has MATH_ERREXCEPT set: FE_DIVBYZERO is raised.

### Example

 ``123456789101112`` ``````/* log example */ #include /* printf */ #include /* log */ int main () { double param, result; param = 5.5; result = log (param); printf ("log(%f) = %f\n", param, result ); return 0; }``````

Output:
 ``` log(5.500000) = 1.704748 ```