roundeven, roundevenf, roundevenl

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Defined in header <math.h>
float       roundevenf( float arg );
 (1) (since C23)
double      roundeven( double arg );
 (2) (since C23)
long double roundevenl( long double arg );
 (3) (since C23)
Defined in header <tgmath.h>
#define roundeven( arg )
 (4) (since C23)
1-3) Computes the nearest integer value to arg (in floating-point format), rounding halfway cases to nearest even integer, regardless of the current rounding mode.
4) Type-generic macro: If arg has type long double, roundevenl is called. Otherwise, if arg has integer type or the type double, roundeven is called. Otherwise, roundevenf is called, respectively.

Parameters

arg - floating-point value

Return value

If no errors occur, the nearest integer value to arg, rounding halfway cases to nearest even integer, 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.

Example

Run this code
#include <math.h>
#include <stdio.h>
 
int main(void)
{
    printf("roundeven(+2.4) = %+.1f\n", roundeven(2.4));
    printf("roundeven(-2.4) = %+.1f\n", roundeven(-2.4));
    printf("roundeven(+2.5) = %+.1f\n", roundeven(2.5));
    printf("roundeven(-2.5) = %+.1f\n", roundeven(-2.5));
    printf("roundeven(+2.6) = %+.1f\n", roundeven(2.6));
    printf("roundeven(-2.6) = %+.1f\n", roundeven(-2.6));
    printf("roundeven(+3.5) = %+.1f\n", roundeven(3.5));
    printf("roundeven(-3.5) = %+.1f\n", roundeven(-3.5));
    printf("roundeven(-0.0) = %+.1f\n", roundeven(-0.0));
    printf("roundeven(-Inf) = %+f\n",   roundeven(-INFINITY));
}

Possible output: 

roundeven(+2.4) = +2.0
roundeven(-2.4) = -2.0
roundeven(+2.5) = +2.0
roundeven(-2.5) = -2.0
roundeven(+2.6) = +3.0
roundeven(-2.6) = -3.0
roundeven(+3.5) = +4.0
roundeven(-3.5) = -4.0
roundeven(-0.0) = -0.0
roundeven(-Inf) = -inf

References

  • C23 standard (ISO/IEC 9899:2024):
  • 7.12.9.8 The roundeven functions (p: 265-266)
  • 7.27 Type-generic math <tgmath.h> (p: 386-390)
  • F.10.6.8 The roundeven functions (p: 532)

See also

(C99)(C99)(C99)(C99)(C99)(C99)(C99)(C99)(C99)
 rounds to an integer using current rounding mode with
exception if the result differs
(function)
(C99)(C99)(C99)(C99)(C99)(C99)(C99)(C99)(C99)
 rounds to nearest integer, rounding away from zero in halfway cases
(function)
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