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HTML rendering created 2025-09-06 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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NAME | LIBRARY | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | ATTRIBUTES | STANDARDS | HISTORY | SEE ALSO | COLOPHON |
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round(3) Library Functions Manual round(3)
round, roundf, roundl - round to nearest integer, away from zero
Math library (libm, -lm)
#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
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.
For an explanation of the terms used in this section, see
attributes(7).
┌──────────────────────────────────────┬───────────────┬─────────┐
│ Interface │ Attribute │ Value │
├──────────────────────────────────────┼───────────────┼─────────┤
│ round(), roundf(), roundl() │ Thread safety │ MT-Safe │
└──────────────────────────────────────┴───────────────┴─────────┘
C11, POSIX.1-2008.
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 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
127 (respectively, 1023), and the number 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.
ceil(3), floor(3), lround(3), nearbyint(3), rint(3), trunc(3)
This page is part of the man-pages (Linux kernel and C library
user-space interface documentation) project. Information about
the project can be found at
⟨https://www.kernel.org/doc/man-pages/⟩. If you have a bug report
for this manual page, see
⟨https://git.kernel.org/pub/scm/docs/man-pages/man-pages.git/tree/CONTRIBUTING⟩.
This page was obtained from the tarball man-pages-6.15.tar.gz
fetched from
⟨https://mirrors.edge.kernel.org/pub/linux/docs/man-pages/⟩ on
2025-08-11. If you discover any rendering problems in this HTML
version of the page, or you believe there is a better or more up-
to-date source for the page, or you have corrections or
improvements to the information in this COLOPHON (which is not
part of the original manual page), send a mail to
man-pages@man7.org
Linux man-pages 6.15 2025-05-17 round(3)
Pages that refer to this page: ceil(3), floor(3), lrint(3), lround(3), rint(3), roundup(3), trunc(3)
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HTML rendering created 2025-09-06 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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