round(3) — Linux manual page

round(3)                Library Functions Manual                round(3)

NAME

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

LIBRARY

       Math library (libm, -lm)

SYNOPSIS

       #include <math.h>

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

   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.

ATTRIBUTES

       For an explanation of the terms used in this section, see
       attributes(7).
       ┌─────────────────────────────────────┬───────────────┬─────────┐
       │ Interface                           │ Attribute     │ Value   │
       ├─────────────────────────────────────┼───────────────┼─────────┤
       │ round(), roundf(), roundl()         │ Thread safety │ MT-Safe │
       └─────────────────────────────────────┴───────────────┴─────────┘

STANDARDS

       C11, POSIX.1-2008.

HISTORY

       glibc 2.1.  C99, POSIX.1-2001.

       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 was 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).)  This
       was removed in POSIX.1-2008.

       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

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Linux man-pages 6.9.1          2024-06-16                       round(3)

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

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