log, logf—natural logarithms #include <math.h>
double log(double x);
float logf(float x);
Description
Return the natural logarithm of x, that is, its logarithm base e
(where e is the base of the natural system of logarithms, 2.71828...).
log and logf are identical save for the return and argument types.
You can use the (non-ANSI) function matherr to specify error
handling for these functions.
Returns
Normally, returns the calculated value. When x is zero, the
returned value is -HUGE_VAL and errno is set to ERANGE.
When x is negative, the returned value is NaN (not a number) and
errno is set to EDOM. You can control the error behavior via
matherr.
Portability
log is ANSI. logf is an extension.