NAME¶

std::nearbyint,std::nearbyintf,std::nearbyintl - std::nearbyint,std::nearbyintf,std::nearbyintl

Synopsis¶

Defined in header <cmath>
float nearbyint ( float num );

double nearbyint ( double num ); (until C++23)

long double nearbyint ( long double num );
/* floating-point-type */ (since C++23)
nearbyint ( /* floating-point-type */ num ); (1)
float nearbyintf( float num ); (2) (since C++11)
long double nearbyintl( long double num ); (3) (since C++11)
Additional overloads (since C++11)
Defined in header <cmath>
template< class Integer > (A)
double nearbyint ( Integer num );

1-3) Rounds the floating-point argument num to an integer value in floating-point
format, using the current rounding mode.
The library provides overloads of std::nearbyint for all cv-unqualified
floating-point types as the type of the parameter.
(since C++23)

A) Additional overloads are provided for all integer types, which are (since C++11)
treated as double.

Parameters¶

num - floating-point or integer value

Return value¶

The nearest integer value to num, according to the current rounding mode, is
returned.

Error handling¶

This function is not subject to any of the errors specified in math_errhandling.

If the implementation supports IEEE floating-point arithmetic (IEC 60559),

* FE_INEXACT is never raised.
* If num is ±∞, it is returned, unmodified.
* If num is ±0, it is returned, unmodified.
* If num is NaN, NaN is returned.

Notes¶

The only difference between std::nearbyint and std::rint is that std::nearbyint
never raises FE_INEXACT.

The largest representable floating-point values are exact integers in all standard
floating-point formats, so std::nearbyint never overflows on its own; however the
result may overflow any integer type (including std::intmax_t), when stored in an
integer variable.

If the current rounding mode is FE_TONEAREST, this function rounds to even in
halfway cases (like std::rint, but unlike std::round).

The additional overloads are not required to be provided exactly as (A). They only
need to be sufficient to ensure that for their argument num of integer type,
std::nearbyint(num) has the same effect as std::nearbyint(static_cast<double>(num)).

Example¶

// Run this code

#include <cfenv>
#include <cmath>
#include <iostream>
#pragma STDC FENV_ACCESS ON

int main()
{
std::fesetround(FE_TONEAREST);
std::cout << "rounding to nearest: \n"
<< "nearbyint(+2.3) = " << std::nearbyint(2.3)
<< " nearbyint(+2.5) = " << std::nearbyint(2.5)
<< " nearbyint(+3.5) = " << std::nearbyint(3.5) << '\n'
<< "nearbyint(-2.3) = " << std::nearbyint(-2.3)
<< " nearbyint(-2.5) = " << std::nearbyint(-2.5)
<< " nearbyint(-3.5) = " << std::nearbyint(-3.5) << '\n';

std::fesetround(FE_DOWNWARD);
std::cout << "rounding down:\n"
<< "nearbyint(+2.3) = " << std::nearbyint(2.3)
<< " nearbyint(+2.5) = " << std::nearbyint(2.5)
<< " nearbyint(+3.5) = " << std::nearbyint(3.5) << '\n'
<< "nearbyint(-2.3) = " << std::nearbyint(-2.3)
<< " nearbyint(-2.5) = " << std::nearbyint(-2.5)
<< " nearbyint(-3.5) = " << std::nearbyint(-3.5) << '\n';

std::cout << "nearbyint(-0.0) = " << std::nearbyint(-0.0) << '\n'
<< "nearbyint(-Inf) = " << std::nearbyint(-INFINITY) << '\n';
}

Output:¶

rounding to nearest:
nearbyint(+2.3) = 2 nearbyint(+2.5) = 2 nearbyint(+3.5) = 4
nearbyint(-2.3) = -2 nearbyint(-2.5) = -2 nearbyint(-3.5) = -4
rounding down:
nearbyint(+2.3) = 2 nearbyint(+2.5) = 2 nearbyint(+3.5) = 3
nearbyint(-2.3) = -3 nearbyint(-2.5) = -3 nearbyint(-3.5) = -4
nearbyint(-0.0) = -0
nearbyint(-Inf) = -inf

See also¶

rint
rintf
rintl
lrint
lrintf
lrintl
llrint
llrintf nearest integer using current rounding mode with
llrintl exception if the result differs
(C++11) (function)
(C++11)
(C++11)
(C++11)
(C++11)
(C++11)
(C++11)
(C++11)
(C++11)
round
roundf
roundl
lround
lroundf
lroundl
llround
llroundf
llroundl nearest integer, rounding away from zero in halfway cases
(C++11) (function)
(C++11)
(C++11)
(C++11)
(C++11)
(C++11)
(C++11)
(C++11)
(C++11)
fegetround
fesetround gets or sets rounding direction
(C++11) (function)
(C++11)
C documentation for
nearbyint