Manpages - log.3

log, logf, logl - natural logarithmic function

  #include <math.h>

  double log(double x);
  float logf(float x);
  long double logl(long double x);

Link with -lm.

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

*logf*(), *logl*():

      _ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L
          || /* Since glibc 2.19: */ _DEFAULT_SOURCE
          || /* Glibc <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE

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).

C99, POSIX.1-2001, POSIX.1-2008.

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.

*cbrt*(3), *clog*(3), *log10*(3), *log1p*(3), *log2*(3), *sqrt*(3)

This page is part of release 5.13 of the Linux man-pages project. A description of the project, information about reporting bugs, and the latest version of this page, can be found at https://www.kernel.org/doc/man-pages/.