Section: POSIX Programmer's Manual (3P)
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.
--- floating-point rounding functions
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.
Upon successful completion, these functions shall return the rounded
The result shall have the same sign as
is NaN, a NaN shall be returned.
is ±0, ±0 shall be returned.
shall be returned.
No errors are defined.
The following sections are informative.
The integral value returned by these functions need not be expressible
The return value should be tested before assigning it to an integer
type to avoid the undefined results of an integer overflow.
The Base Definitions volume of POSIX.1-2017,
Section 4.20, Treatment of Error Conditions for Mathematical Functions,
Portions of this text are reprinted and reproduced in electronic form
from IEEE Std 1003.1-2017, Standard for Information Technology
-- Portable Operating System Interface (POSIX), The Open Group Base
Specifications Issue 7, 2018 Edition,
Copyright (C) 2018 by the Institute of
Electrical and Electronics Engineers, Inc and The Open Group.
In the event of any discrepancy between this version and the original IEEE and
The Open Group Standard, the original IEEE and The Open Group Standard
is the referee document. The original Standard can be obtained online at
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