function
<cmath> <ctgmath>

nearbyint

     double nearbyint  (double x);
      float nearbyintf (float x);
long double nearbyintl (long double x);

     double nearbyint (double x);
      float nearbyint (float x);
long double nearbyint (long double x);
     double nearbyint (T x);           // additional overloads for integral types
Round to nearby integral value
Rounds x to an integral value, using the rounding direction specified by fegetround.

This function does not raise FE_INEXACT exceptions. See rint for an equivalent function that may do.

Header <tgmath.h> provides a type-generic macro version of this function.
Additional overloads are provided in this header (<cmath>) for the integral types: These overloads effectively cast x to a double before calculations (defined for T being any integral type).

Parameters

x
Value to round.

Return Value

The value of x rounded to a nearby integral (as a floating-point value).

Example

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/* nearbyint example */
#include <stdio.h>      /* printf */
#include <fenv.h>       /* fegetround, FE_* */
#include <math.h>       /* nearbyint */

int main ()
{
  printf ("rounding using ");
  switch (fegetround()) {
    case FE_DOWNWARD: printf ("downward"); break;
    case FE_TONEAREST: printf ("to-nearest"); break;
    case FE_TOWARDZERO: printf ("toward-zero"); break;
    case FE_UPWARD: printf ("upward"); break;
    default: printf ("unknown");
  }
  printf (" rounding:\n");

  printf ( "nearbyint (2.3) = %.1f\n", nearbyint(2.3) );
  printf ( "nearbyint (3.8) = %.1f\n", nearbyint(3.8) );
  printf ( "nearbyint (-2.3) = %.1f\n", nearbyint(-2.3) );
  printf ( "nearbyint (-3.8) = %.1f\n", nearbyint(-3.8) );
  return 0;
}


Possible output:

Rounding using to-nearest rounding:
nearbyint (2.3) = 2.0
nearbyint (3.8) = 4.0
nearbyint (-2.3) = -2.0
nearbyint (-3.8) = -4.0

See also

rint
Round to integral value (function )
lrint
Round and cast to long integer (function )
round
Round to nearest (function )
floor
Round down value (function )
ceil
Round up value (function )
trunc
Truncate value (function )

C++