round

Section: C Library Functions (3)
Updated: 202-0-08
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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	M-Safe

 

STANDARDS

C11, POSIX.-2008.  

HISTORY

glibc 2.1. C99, POSIX.-2001. POSIX.-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 erro-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 IEE-754 standard 3-bit and 6-bit floatin-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.-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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Index

NAME

LIBRARY

SYNOPSIS

DESCRIPTION

RETURN VALUE

ERRORS

ATTRIBUTES

STANDARDS

HISTORY

SEE ALSO