NAME

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

Synopsis

Defined in header <cmath>
float nearbyint ( float arg ); (1) (since C++11)
float nearbyintf( float arg );
double nearbyint ( double arg ); (2) (since C++11)
long double nearbyint ( long double arg ); (3) (since C++11)
long double nearbyintl( long double arg );
double nearbyint ( IntegralType arg ); (4) (since C++11)

1-3) Rounds the floating-point argument arg to an integer value in floating-point
format, using the current rounding mode.
4) A set of overloads or a function template accepting an argument of any integral
type. Equivalent to (2) (the argument is cast to double).

Parameters

arg - floating point value

Return value

The nearest integer value to arg, 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 arg is ±∞, it is returned, unmodified
* If arg is ±0, it is returned, unmodified
* If arg 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 rint, but unlike round).

Example

// Run this code

#include <iostream>
#include <cmath>
#include <cfenv>

int main()
{
#pragma STDC FENV_ACCESS ON
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