nearbyint - Man Page

floating-point rounding functions


This manual page is part of the POSIX Programmer's Manual. The Linux implementation of this interface may differ (consult the corresponding Linux manual page for details of Linux behavior), or the interface may not be implemented on Linux.


#include <math.h>

double nearbyint(double x);
float nearbyintf(float x);
long double nearbyintl(long double x);


The functionality described on this reference page is aligned with the ISO C standard. Any conflict between the requirements described here and the ISO C standard is unintentional. This volume of POSIX.1-2017 defers to the ISO C standard.

These functions shall round their argument to an integer value in floating-point format, using the current rounding direction and without raising the inexact floating-point exception.

Return Value

Upon successful completion, these functions shall return the rounded integer value. The result shall have the same sign as x.

If x is NaN, a NaN shall be returned.

If x is ±0, ±0 shall be returned.

If x is ±Inf, x shall be returned.


No errors are defined.

The following sections are informative.



Application Usage

The integral value returned by these functions need not be expressible as an intmax_t. The return value should be tested before assigning it to an integer type to avoid the undefined results of an integer overflow.



Future Directions


See Also

feclearexcept(), fetestexcept()

The Base Definitions volume of POSIX.1-2017, Section 4.20, Treatment of Error Conditions for Mathematical Functions, <math.h>

Referenced By

math.h(0p), rint(3p).

2017 IEEE/The Open Group POSIX Programmer's Manual