ROUND
Section: Linux Programmer's Manual (3)
Updated: 20130621
Index
Return to Main Contents
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);
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
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.12001 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 threadsafe.
CONFORMING TO
C99, POSIX.12001.
NOTES
POSIX.12001 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 errorhandling 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 IEEE754 standard 32bit and 64bit floatingpoint 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 3.74 of the Linux
manpages
project.
A description of the project,
information about reporting bugs,
and the latest version of this page,
can be found at
http://www.kernel.org/doc/manpages/.
Index
 NAME

 SYNOPSIS

 DESCRIPTION

 RETURN VALUE

 ERRORS

 VERSIONS

 ATTRIBUTES

 Multithreading (see pthreads(7))

 CONFORMING TO

 NOTES

 SEE ALSO

 COLOPHON
