Linux manual pages Section 3: Subroutines  

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);
 
[Note] Note
Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
round(), roundf(), roundl():
_XOPEN_SOURCE >= 600 || _ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L;
or cc -std=c99
[Note] Note

Link with −lm.

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

Multithreading (see pthreads(7))

The round(), roundf(), and roundl() functions are thread-safe.

CONFORMING TO

C99, POSIX.1-2001.

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 3.52 of the Linux man-pages project. A description of the project, and information about reporting bugs, can be found at http://www.kernel.org/doc/man−pages/.


  Copyright 2001 Andries Brouwer <aebcwi.nl>.
and Copyright 2008, Linux Foundation, written by Michael Kerrisk
    <mtk.manpagesgmail.com>

%%%LICENSE_START(VERBATIM)
Permission is granted to make and distribute verbatim copies of this
manual provided the copyright notice and this permission notice are
preserved on all copies.

Permission is granted to copy and distribute modified versions of this
manual under the conditions for verbatim copying, provided that the
entire resulting derived work is distributed under the terms of a
permission notice identical to this one.

Since the Linux kernel and libraries are constantly changing, this
manual page may be incorrect or out-of-date.  The author(s) assume no
responsibility for errors or omissions, or for damages resulting from
the use of the information contained herein.  The author(s) may not
have taken the same level of care in the production of this manual,
which is licensed free of charge, as they might when working
professionally.

Formatted or processed versions of this manual, if unaccompanied by
the source, must acknowledge the copyright and authors of this work.
%%%LICENSE_END