| NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | VERSIONS | CONFORMING TO | NOTES | SEE ALSO | COLOPHON | The Linux Programming Interface |
ROUND(3) Linux Programmer's Manual ROUND(3)
round, roundf, roundl - round to nearest integer, away from zero
#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():
_XOPEN_SOURCE >= 600 || _ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L;
or cc -std=c99
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.
These functions return the rounded integer value.
If x is integral, +0, -0, NaN, or infinite, x itself is returned.
No errors occur. POSIX.1-2001 documents a range error for overflows, but see
NOTES.
These functions first appeared in glibc in version 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 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.
ceil(3), floor(3), lround(3), nearbyint(3), rint(3), trunc(3)
This page is part of release 3.32 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/.
2010-09-20 ROUND(3)
HTML rendering created 2010-12-03 by Michael Kerrisk, author of The Linux Programming Interface