log(3p) — Linux manual page


LOG(3P)                 POSIX Programmer's Manual                LOG(3P)

PROLOG         top

       This manual page is part of the POSIX Programmer's Manual.  The
       Linux implementation of this interface may differ (consult the
       corresponding Linux manual page for details of Linux behavior),
       or the interface may not be implemented on Linux.

NAME         top

       log, logf, logl — natural logarithm function

SYNOPSIS         top

       #include <math.h>

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

DESCRIPTION         top

       The functionality described on this reference page is aligned
       with the ISO C standard. Any conflict between the requirements
       described here and the ISO C standard is unintentional. This
       volume of POSIX.1‐2017 defers to the ISO C standard.

       These functions shall compute the natural logarithm of their
       argument x, loge(x).

       An application wishing to check for error situations should set
       errno to zero and call feclearexcept(FE_ALL_EXCEPT) before
       calling these functions. On return, if errno is non-zero or
       fetestexcept(FE_INVALID | FE_DIVBYZERO | FE_OVERFLOW |
       FE_UNDERFLOW) is non-zero, an error has occurred.

RETURN VALUE         top

       Upon successful completion, these functions shall return the
       natural logarithm of x.

       If x is ±0, a pole error shall occur and log(), logf(), and
       logl() shall return -HUGE_VAL, -HUGE_VALF, and -HUGE_VALL,

       For finite values of x that are less than 0, or if x is -Inf, a
       domain error shall occur, and either a NaN (if supported), or an
       implementation-defined value shall be returned.

       If x is NaN, a NaN shall be returned.

       If x is 1, +0 shall be returned.

       If x is +Inf, x shall be returned.

ERRORS         top

       These functions shall fail if:

       Domain Error
                   The finite value of x is negative, or x is -Inf.

                   If the integer expression (math_errhandling &
                   MATH_ERRNO) is non-zero, then errno shall be set to
                   [EDOM].  If the integer expression (math_errhandling
                   & MATH_ERREXCEPT) is non-zero, then the invalid
                   floating-point exception shall be raised.

       Pole Error  The value of x is zero.

                   If the integer expression (math_errhandling &
                   MATH_ERRNO) is non-zero, then errno shall be set to
                   [ERANGE].  If the integer expression
                   (math_errhandling & MATH_ERREXCEPT) is non-zero, then
                   the divide-by-zero floating-point exception shall be

       The following sections are informative.

EXAMPLES         top



       On error, the expressions (math_errhandling & MATH_ERRNO) and
       (math_errhandling & MATH_ERREXCEPT) are independent of each
       other, but at least one of them must be non-zero.

RATIONALE         top




SEE ALSO         top

       exp(3p), feclearexcept(3p), fetestexcept(3p), isnan(3p),
       log10(3p), log1p(3p)

       The Base Definitions volume of POSIX.1‐2017, Section 4.20,
       Treatment of Error Conditions for Mathematical Functions,

COPYRIGHT         top

       Portions of this text are reprinted and reproduced in electronic
       form from IEEE Std 1003.1-2017, Standard for Information
       Technology -- Portable Operating System Interface (POSIX), The
       Open Group Base Specifications Issue 7, 2018 Edition, Copyright
       (C) 2018 by the Institute of Electrical and Electronics
       Engineers, Inc and The Open Group.  In the event of any
       discrepancy between this version and the original IEEE and The
       Open Group Standard, the original IEEE and The Open Group
       Standard is the referee document. The original Standard can be
       obtained online at http://www.opengroup.org/unix/online.html .

       Any typographical or formatting errors that appear in this page
       are most likely to have been introduced during the conversion of
       the source files to man page format. To report such errors, see
       https://www.kernel.org/doc/man-pages/reporting_bugs.html .

IEEE/The Open Group               2017                           LOG(3P)

Pages that refer to this page: math.h(0p)exp2(3p)exp(3p)log10(3p)log1p(3p)log2(3p)logf(3p)