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 maxi-
mum 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 num-
ber 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)
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