Open Source Software

round(3)



NAME

   round, roundf, roundl - round to nearest integer, away from zero

SYNOPSIS

   #include <math.h>

   double round(double x);
   float roundf(float x);
   long double roundl(long double x);

   Link with -lm.

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

   round(), roundf(), roundl():
       _ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L

DESCRIPTION

   These functions round x to the nearest integer, but round halfway cases
   away from zero (regardless  of  the  current  rounding  direction,  see
   fenv(3)), instead of to the nearest even integer like rint(3).

   For example, round(0.5) is 1.0, and round(-0.5) is -1.0.

RETURN VALUE

   These functions return the rounded integer value.

   If x is integral, +0, -0, NaN,  or infinite, x itself is returned.

ERRORS

   No  errors  occur.  POSIX.1-2001 documents a range error for overflows,
   but see NOTES.

VERSIONS

   These functions first appeared in glibc in version 2.1.

ATTRIBUTES

   For  an  explanation  of  the  terms  used   in   this   section,   see
   attributes(7).

   
   Interface                    Attribute      Value   
   
   round(), roundf(), roundl()  Thread safety  MT-Safe

CONFORMING TO

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

NOTES

   POSIX.1-2001  contains  text  about  overflow (which might set errno to
   ERANGE, or raise an FE_OVERFLOW exception).  In  practice,  the  result
   cannot overflow on any current machine, so this error-handling stuff is
   just nonsense.  (More precisely, overflow  can  happen  only  when  the
   maximum  value  of  the exponent is smaller than the number of mantissa
   bits.  For the  IEEE-754  standard  32-bit  and  64-bit  floating-point
   numbers  the maximum value of the exponent is 128 (respectively, 1024),
   and the number of mantissa bits is 24 (respectively, 53).)

   If you want to store the rounded value in an integer type, you probably
   want to use one of the functions described in lround(3) instead.

SEE ALSO

   ceil(3), floor(3), lround(3), nearbyint(3), rint(3), trunc(3)

COLOPHON

   This  page  is  part of release 4.09 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/.

                              2016-03-15                          ROUND(3)



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