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log(3p) — Linux manual page

LOG(3P)                 POSIX Programmer's ManualLOG(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(doublex);       float logf(floatx);       long double logl(long doublex);

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       argumentx, loge(x).       An application wishing to check for error situations should seterrno to zero and callfeclearexcept(FE_ALL_EXCEPT) before calling       these functions. On return, iferrno is non-zero orfetestexcept(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 ofx.       Ifx is ±0, a pole error shall occur andlog(),logf(), andlogl()       shall return -HUGE_VAL, -HUGE_VALF, and -HUGE_VALL, respectively.       For finite values ofx that are less than 0, or ifx is -Inf, a       domain error shall occur, and either a NaN (if supported), or an       implementation-defined value shall be returned.       Ifx is NaN, a NaN shall be returned.       Ifx is 1, +0 shall be returned.       Ifx is +Inf,x shall be returned.

ERRORS        top

       These functions shall fail if:       Domain Error                   The finite value ofx is negative, orx is -Inf.                   If the integer expression (math_errhandling &                   MATH_ERRNO) is non-zero, thenerrno 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 ofx is zero.                   If the integer expression (math_errhandling &                   MATH_ERRNO) is non-zero, thenerrno 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 raised.The following sections are informative.

EXAMPLES        top

       None.

APPLICATION USAGE        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

       None.

FUTURE DIRECTIONS        top

       None.

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,math.h(0p)

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 athttp://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, seehttps://www.kernel.org/doc/man-pages/reporting_bugs.html .IEEE/The Open Group                2017LOG(3P)

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

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