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std::nearbyint

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nearbyint
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Defined in header <cmath>
float       nearbyint( float arg );
(since C++11)
double      nearbyint( double arg );
(since C++11)
long double nearbyint( long double arg );
(since C++11)
double      nearbyint( Integral arg );
(since C++11)

Rounds the floating-point argument arg to an integer value in floating-point format, using the current rounding mode.

Contents

[edit] Parameters

arg - floating point value

[edit] Return value

The integer result of rounding arg

[edit] Notes

The only difference between std::nearbyint and std::rint is that std::rint may raise the FE_INEXACT floating-point exception, while std::nearbyint never raises it.

[edit] Example

#include <cmath>
#include <cfenv>
#include <iostream>
 
int main()
{
    #pragma STDC FENV_ACCESS ON
    std::fesetround(FE_DOWNWARD);
    std::cout << "rounding using FE_DOWNWARD: \n" << std::fixed
              << " 12.0 ->  " << std::nearbyint(12.0) << '\n'
              << " 12.1 ->  " << std::nearbyint(12.1) << '\n'
              << "-12.1 -> " << std::nearbyint(-12.1) << '\n'
              << " 12.5 ->  " << std::nearbyint(12.5) << '\n'
              << " 12.9 ->  " << std::nearbyint(12.9) << '\n'
              << "-12.9 -> " << std::nearbyint(-12.9) << '\n'
              << " 13.0 ->  " << std::nearbyint(13.0) << '\n';
    std::fesetround(FE_TONEAREST);
    std::cout << "rounding using FE_TONEAREST: \n"
              << " 12.0 ->  " << std::nearbyint(12.0) << '\n'
              << " 12.1 ->  " << std::nearbyint(12.1) << '\n'
              << "-12.1 -> " << std::nearbyint(-12.1) << '\n'
              << " 12.5 ->  " << std::nearbyint(12.5) << '\n'
              << " 12.9 ->  " << std::nearbyint(12.9) << '\n'
              << "-12.9 -> " << std::nearbyint(-12.9) << '\n'
              << " 13.0 ->  " << std::nearbyint(13.0) << '\n';
}

Output:

rounding using FE_DOWNWARD:
 12.0 ->  12.000000
 12.1 ->  12.000000
-12.1 -> -13.000000
 12.5 ->  12.000000
 12.9 ->  12.000000
-12.9 -> -13.000000
 13.0 ->  13.000000
rounding using FE_TONEAREST: 
 12.0 ->  12.000000
 12.1 ->  12.000000
-12.1 -> -12.000000
 12.5 ->  12.000000
 12.9 ->  13.000000
-12.9 -> -13.000000
 13.0 ->  13.000000

[edit] See also

(C++11)(C++11)(C++11)
nearest integer using current rounding mode with
exception if the result differs
(function) [edit]
(C++11)(C++11)(C++11)
nearest integer, rounding away from zero in halfway cases
(function) [edit]
(C++11)(C++11)
gets or sets rounding direction
(function) [edit]