roundl (3)
Leading comments
Copyright 2001 Andries Brouwer <aeb@cwi.nl>. and Copyright 2008, Linux Foundation, written by Michael Kerrisk <mtk.manpages@gmail.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 wor...
NAME
round, roundf, roundl  round to nearest integer, away from zeroSYNOPSIS
#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
For an explanation of the terms used in this section, see attributes(7).Interface  Attribute  Value 
round(), roundf(), roundl()  Thread safety  MTSafe 
CONFORMING TO
C99, POSIX.12001, POSIX.12008.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.