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():
_ISOC99_SOURCE ||
_POSIX_C_SOURCE >= 200112L
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.
For an explanation of the terms used in this section, see
attributes(7).
| Interface |
Attribute |
Value |
| round (), roundf (), roundl () |
Thread safety |
MT-Safe |
C99, POSIX.1-2001, POSIX.1-2008.
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)