round(), roundf(), roundl()

Round a number to the closest integer

Synopsis:

#include <math.h>

double round( double x );

float roundf( float x );

long double roundl( long double x );

Arguments:

x: The number you want to round.

Library:

libm

Use the -l m option to qcc to link against this library.

Description:

The round(), roundf(), and roundl() functions return x rounded to the nearest integer n, rounding halfway cases away from zero, regardless of the current rounding direction (i.e., returning the value with larger magnitude if |n − x| == 1/2).

To check for error situations, use feclearexcept() and fetestexcept(). For example:

Call feclearexcept(FE_ALL_EXCEPT) before calling round(), roundf(), or roundl().
On return, if fetestexcept(FE_ALL_EXCEPT) is nonzero, then an error has occurred.

Returns:

The rounded value.

If `x` is:	rint() returns:	Errors:
±Inf	`x`	—
NaN	`x`	—

These functions raise FE_INEXACT if the FPU reports that the result can't be exactly represented as a floating-point number.

Examples:

#include <math.h>
#include <stdio.h>
#include <stdlib.h>
#include <fenv.h>

int main (void)
{
  int except_flags;
  double num1, result1;

  for (num1 = 3.0; num1 <= 4.0; num1 += 0.1)
  {
    feclearexcept(FE_ALL_EXCEPT);
    result1 = round (num1);
    except_flags = fetestexcept(FE_ALL_EXCEPT);
    if (except_flags) {
      /* An error occurred; handle it appropriately. */
    } else {
      printf ("Rounding %f gives %f\n", num1, result1);
    }
  }

  return (EXIT_SUCCESS);
}

Classification:

ANSI, POSIX 1003.1

Safety:
Cancellation point	No
Interrupt handler	No
Signal handler	No
Thread	Yes