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NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | VERSIONS | ATTRIBUTES | CONFORMING TO | NOTES | SEE ALSO | COLOPHON |
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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():
_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)
This page is part of release 4.15 of the Linux man-pages project. A
description of the project, information about reporting bugs, and the
latest version of this page, can be found at
https://www.kernel.org/doc/man-pages/.
2017-09-15 ROUND(3)
Pages that refer to this page: ceil(3), floor(3), lrint(3), lround(3), rint(3), trunc(3)
Copyright and license for this manual page
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