nearbyint, nearbyintf, nearbyintl

float       nearbyintf( float arg );

double      nearbyint( double arg );

long double nearbyintl( long double arg );

#define nearbyint( arg )

Parameters

Return value

The nearest integer value to arg, 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 arg is ±∞, it is returned, unmodified
• If arg is ±0, it is returned, unmodified
• If arg is NaN, NaN is returned

Notes

The only difference between nearbyint and rint is that nearbyint never raises FE_INEXACT.

The largest representable floating-point values are exact integers in all standard floating-point formats, so nearbyint never overflows on its own; however the result may overflow any integer type (including 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 rint, but unlike round).

Example

#include <stdio.h>
#include <math.h>
#include <fenv.h>
 
int main(void)
{
#pragma STDC FENV_ACCESS ON
    fesetround(FE_TONEAREST);
    printf("rounding to nearest:\nnearbyint(+2.3) = %+.1f  ", nearbyint(2.3));
    printf("nearbyint(+2.5) = %+.1f  ", nearbyint(2.5));
    printf("nearbyint(+3.5) = %+.1f\n", nearbyint(3.5));
    printf("nearbyint(-2.3) = %+.1f  ", nearbyint(-2.3));
    printf("nearbyint(-2.5) = %+.1f  ", nearbyint(-2.5));
    printf("nearbyint(-3.5) = %+.1f\n", nearbyint(-3.5));
 
    fesetround(FE_DOWNWARD);
    printf("rounding down: \nnearbyint(+2.3) = %+.1f  ", nearbyint(2.3));
    printf("nearbyint(+2.5) = %+.1f  ", nearbyint(2.5));
    printf("nearbyint(+3.5) = %+.1f\n", nearbyint(3.5));
    printf("nearbyint(-2.3) = %+.1f  ", nearbyint(-2.3));
    printf("nearbyint(-2.5) = %+.1f  ", nearbyint(-2.5));
    printf("nearbyint(-3.5) = %+.1f\n", nearbyint(-3.5));
 
    printf("nearbyint(-0.0) = %+.1f\n", nearbyint(-0.0));
    printf("nearbyint(-Inf) = %+.1f\n", nearbyint(-INFINITY));
}

rounding to nearest:
nearbyint(+2.3) = +2.0  nearbyint(+2.5) = +2.0  nearbyint(+3.5) = +4.0
nearbyint(-2.3) = -2.0  nearbyint(-2.5) = -2.0  nearbyint(-3.5) = -4.0
rounding down: 
nearbyint(+2.3) = +2.0  nearbyint(+2.5) = +2.0  nearbyint(+3.5) = +3.0
nearbyint(-2.3) = -3.0  nearbyint(-2.5) = -3.0  nearbyint(-3.5) = -4.0
nearbyint(-0.0) = -0.0
nearbyint(-Inf) = -inf

References

• C11 standard (ISO/IEC 9899:2011):
• 7.12.9.3 The nearbyint functions (p: 251-252)
• 7.25 Type-generic math <tgmath.h> (p: 373-375)
• F.10.6.3 The nearbyint functions (p: 526)
• C99 standard (ISO/IEC 9899:1999):
• 7.12.9.3 The nearbyint functions (p: 232)
• 7.22 Type-generic math <tgmath.h> (p: 335-337)
• F.9.6.3 The nearbyint functions (p: 463)

See also