round(3) — Linux manual page


round(3)                Library Functions Manual                round(3)

NAME         top

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

LIBRARY         top

       Math library (libm, -lm)

SYNOPSIS         top

       #include <math.h>

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

   Feature Test Macro Requirements for glibc (see

       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.

ATTRIBUTES         top

       For an explanation of the terms used in this section, see
       │ Interface                           Attribute     Value   │
       │ round(), roundf(), roundl()         │ Thread safety │ MT-Safe │

STANDARDS         top

       C11, POSIX.1-2008.

HISTORY         top

       glibc 2.1.  C99, POSIX.1-2001.

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 127 (respectively, 1023), and the number of mantissa
       bits including the implicit bit 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)

Linux man-pages (unreleased)     (date)                         round(3)

Pages that refer to this page: ceil(3)floor(3)lrint(3)lround(3)rint(3)roundup(3)trunc(3)