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: The general-purpose math library.
libm-sve: (QNX Neutrino 7.1 or later) A library that optimizes the code for ARMv8.2 chips that have Scalable Vector Extension hardware.

Your system requirements will determine how you should work with these libraries:

If you want only selected processes to run with the SVE version, you can include both libraries in your OS image and use the -l m or -l m-sve option to qcc to link explicitly against the appropriate one.
If you want all processes to use the SVE version, include libm-sve.so in your OS image and set up a symbolic link from libm.so to libm-sve.so. Use the -l m option to qcc to link against the library.

Note: Compile your program with the -fno-builtin option to prevent the compiler from using a built-in version of the function.

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:

C11, POSIX 1003.1

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