std::nearbyint,std::nearbyintf,std::nearbyintl(3)

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

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)