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 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