log, logf, logl - natural logarithmic function

Math library (`libm`

, `-lm`

)

```
#include <math.h>
double log(double x);
float logf(float x);
long double logl(long double x);
```

Feature Test Macro Requirements for glibc (see feature_test_macros(7)):

These functions return the natural logarithm of `x`

.

On success, these functions return the natural logarithm of
`x`

.

If `x`

is a NaN, a NaN is returned.

If `x`

is 1, the result is +0.

If `x`

is positive infinity, positive infinity is
returned.

If `x`

is zero, then a pole error occurs, and the functions
return -**HUGE_VAL**, -**HUGE_VALF**, or
-**HUGE_VALL**, respectively.

If `x`

is negative (including negative infinity), then a
domain error occurs, and a NaN (not a number) is returned.

See math_error(7) for information on how to determine whether an error has occurred when calling these functions.

The following errors can occur:

- Domain error:
`x`

is negative -
`errno`

is set to**EDOM**. An invalid floating-point exception (**FE_INVALID**) is raised. - Pole error:
`x`

is zero -
`errno`

is set to**ERANGE**. A divide-by-zero floating-point exception (**FE_DIVBYZERO**) is raised.

For an explanation of the terms used in this section, see attributes(7).

Interface | Attribute | Value |

Thread safety | MT-Safe |

C11, POSIX.1-2008.

C99, POSIX.1-2001.

The variant returning `double`

also conforms to SVr4, 4.3BSD,
C89.

In glibc 2.5 and earlier, taking the log() of a NaN
produces a bogus invalid floating-point (**FE_INVALID**)
exception.