LOG(3) Library Functions Manual LOG(3)

log — natural logarithm function

#include <math.h>

double log(double x);

The log() function computes the natural logarithm of x, log e ( x ). The value of x must be positive.

An application wishing to check for error situations should set errno to 0 before calling log(). If errno is non-zero on return, or the return value is NaN, an error has occurred.

Upon successful completion, log() returns the natural logarithm of x .

If x is NaN, NaN is returned and errno may be set to [EDOM].

If x is less than 0, -HUGE_VAL or NaN is returned, and errno is set to [EDOM].

If x is 0, -HUGE_VAL is returned and errno may be set to [ERANGE].

The log() function will fail if:

The value of x is negative.

The log() function may fail if:

The value of x is NaN.
The value of x is 0.

No other errors will occur.

None.

None.

None.

exp(3) , isnan(3) , log10(3) , log1p(3) , <math.h> .

Derived from Issue 1 of the SVID.

February 1997 posix.fail