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rint(3) Library Functions Manual rint(3)


nearbyint, nearbyintf, nearbyintl, rint, rintf, rintl - round to nearest integer


Math library (libm, -lm)


#include <math.h>
double nearbyint(double x);
float nearbyintf(float x);
long double nearbyintl(long double x);
double rint(double x);
float rintf(float x);
long double rintl(long double x);

Feature Test Macro Requirements for glibc (see feature_test_macros(7)):

nearbyint(), nearbyintf(), nearbyintl():



|| _XOPEN_SOURCE >= 500
|| /* Since glibc 2.19: */ _DEFAULT_SOURCE
|| /* glibc <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE

rintf(), rintl():

|| /* Since glibc 2.19: */ _DEFAULT_SOURCE
|| /* glibc <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE


The nearbyint(), nearbyintf(), and nearbyintl() functions round their argument to an integer value in floating-point format, using the current rounding direction (see fesetround(3)) and without raising the inexact exception. When the current rounding direction is to nearest, these functions round halfway cases to the even integer in accordance with IEEE-754.

The rint(), rintf(), and rintl() functions do the same, but will raise the inexact exception (FE_INEXACT, checkable via fetestexcept(3)) when the result differs in value from the argument.


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.


For an explanation of the terms used in this section, see attributes(7).

Interface Attribute Value
nearbyint (), nearbyintf (), nearbyintl (), rint (), rintf (), rintl () Thread safety MT-Safe


C99, POSIX.1-2001, POSIX.1-2008.


SUSv2 and POSIX.1-2001 contain 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 127 (respectively, 1023), and the number of mantissa bits including the implicit bit 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 lrint(3) instead.


ceil(3), floor(3), lrint(3), round(3), trunc(3)

2023-02-05 Linux man-pages 6.03