round(3) — Linux manual page


ROUND(3)                  Linux Programmer's Manual                 ROUND(3)

NAME         top

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

SYNOPSIS         top

       #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         top

       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         top

       These functions return the rounded integer value.

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

ERRORS         top

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

VERSIONS         top

       These functions first appeared in glibc in version 2.1.

ATTRIBUTES         top

       For an explanation of the terms used in this section, see

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

CONFORMING TO         top

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

NOTES         top

       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)

SEE ALSO         top

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

COLOPHON         top

       This page is part of release 5.08 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

                                 2017-09-15                         ROUND(3)

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