nearbyint, nearbyintf, nearbyintl

 

C

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Date and time utilities

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Concurrency support (C11)

Technical Specifications

Symbol index

 

Numerics

Common mathematical functions

Floating-point environment (C99)

Pseudo-random number generation

Complex number arithmetic (C99)

Type-generic math (C99)

 

Common mathematical functions

Types
div_tldiv_tlldiv_timaxdiv_t (C99)(C99)     float_tdouble_t (C99)(C99)     _Decimal32_t_Decimal64_t (C23)(C23)
Functions
Basic operations abslabsllabsimaxabs (C99)(C99) fabs divldivlldivimaxdiv (C99)(C99) fmod remainder (C99) remquo (C99) fma (C99) fdim (C99) nannanfnanlnandN (C99)(C99)(C99)(C23) Maximum/minimum operations fmax (C99) fmaximum (C23) fmaximum_mag (C23) fmaximum_num (C23) fmaximum_mag_num (C23)     fmin (C99) fminimum (C23) fminimum_mag (C23) fminimum_num (C23) fminimum_mag_num (C23) Exponential functions exp exp10 (C23) exp2 (C99) expm1 (C99) exp10m1 (C23) exp2m1 (C23) log log10 log2 (C99) log1plogp1 (C99)(C23) log10p1 (C23) log2p1 (C23) Power functions sqrt cbrt (C99) rootn (C23) rsqrt (C23) hypot (C99) compound (C23) pow pown (C23) powr (C23) Trigonometric and hyperbolic functions sin cos tan asin acos atan atan2 sinpi (C23) cospi (C23) tanpi (C23) asinpi (C23) acospi (C23) atanpi (C23) atan2pi (C23) sinh cosh tanh asinh (C99) acosh (C99) atanh (C99)	Error and gamma functions erf (C99) erfc (C99) lgamma (C99) tgamma (C99) Nearest integer floating-point operations ceil floor roundlroundllround (C99)(C99)(C99) roundeven (C23) trunc (C99) nearbyint (C99) rintlrintllrint (C99)(C99)(C99) fromfpfromfpxufromfpufromfpx (C23)(C23)(C23)(C23) Floating-point manipulation functions ldexp frexp scalbnscalbln (C99)(C99) ilogbllogb (C99)(C23) logb (C99) modf nextafternexttoward (C99)(C99) nextupnextdown (C23)(C23) copysign (C99) canonicalize (C23) Narrowing operations fadd (C23) fsub (C23) fmul (C23) fdiv (C23) ffma (C23) fsqrt (C23) Quantum and quantum exponent functions quantizedN (C23) samequantumdN (C23) quantumdN (C23) llquantexpdN (C23) Decimal re-encoding functions encodedecdN (C23) decodedecdN (C23) encodebindN (C23) decodebindN (C23) Total order and payload functions totalorder (C23) getpayload (C23) setpayload (C23) setpayloadsig (C23) Classification fpclassify (C99) iscanonical (C23) isfinite (C99) isinf (C99) isnan (C99) isnormal (C99) signbit (C99) issubnormal (C23) iszero (C23) isgreater (C99) isgreaterequal (C99) isless (C99) islessequal (C99) islessgreater (C99) isunordered (C99) issignaling (C23) iseqsig (C23)
Macro constants
Special floating-point values HUGE_VALFHUGE_VALHUGE_VALLHUGE_VALDN (C99)(C99)(C23) INFINITYDEC_INFINITY (C99)(C23) NANDEC_NAN (C99)(C23) Arguments and return values FP_ILOGB0FP_ILOGBNAN (C99)(C99) FP_INT_UPWARDFP_INT_DOWNWARDFP_INT_TOWARDZEROFP_INT_TONEARESTFROMZEROFP_INT_TONEAREST (C23)(C23)(C23)(C23)(C23)     FP_LLOGB0FP_LLOGBNAN (C23)(C23) FP_NORMALFP_SUBNORMALFP_ZEROFP_INFINITEFP_NAN (C99)(C99)(C99)(C99)(C99)     Error handling MATH_ERRNOMATH_ERRNOEXCEPT (C99)(C99) math_errhandling (C99)	Fast operation indicators FP_FAST_FMAFFP_FAST_FMA (C99)(C99) FP_FAST_FADDFP_FAST_FADDLFP_FAST_DADDLFP_FAST_DMADDDN (C23)(C23)(C23)(C23)     FP_FAST_FMULFP_FAST_FMULLFP_FAST_DMULLFP_FAST_DMMULDN (C23)(C23)(C23)(C23) FP_FAST_FFMAFP_FAST_FFMALFP_FAST_DFMALFP_FAST_DMFMADN (C23)(C23)(C23)(C23) FP_FAST_FMALFP_FAST_FMADN (C99)(C23) FP_FAST_FSUBFP_FAST_FSUBLFP_FAST_DSUBLFP_FAST_DMSUBDN (C23)(C23)(C23)(C23) FP_FAST_FDIVFP_FAST_FDIVLFP_FAST_DDIVLFP_FAST_DMDIVDN (C23)(C23)(C23)(C23) FP_FAST_FSQRTFP_FAST_FSQRTLFP_FAST_DSQRTLFP_FAST_DMSQRTDN (C23)(C23)(C23)(C23)

 

Defined in header <math.h>
float       nearbyintf( float arg );	(1)	(since C99)
double      nearbyint( double arg );	(2)	(since C99)
long double nearbyintl( long double arg );	(3)	(since C99)
Defined in header <tgmath.h>
#define nearbyint( arg )	(4)	(since C99)

1-3) Rounds the floating-point argument arg to an integer value in floating-point format, using the current rounding mode.

4) Type-generic macro: If arg has type long double, nearbyintl is called. Otherwise, if arg has integer type or the type double, nearbyint is called. Otherwise, nearbyintf is called, respectively.

Parameters

arg

-

floating-point value

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

Run this code

#include <fenv.h>
#include <math.h>
#include <stdio.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));
}

Output:

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

• C23 standard (ISO/IEC 9899:2024):

• 7.12.9.3 The nearbyint functions (p: TBD)

• 7.25 Type-generic math <tgmath.h> (p: TBD)

• F.10.6.3 The nearbyint functions (p: TBD)

• C17 standard (ISO/IEC 9899:2018):

• 7.12.9.3 The nearbyint functions (p: TBD)

• 7.25 Type-generic math <tgmath.h> (p: TBD)

• F.10.6.3 The nearbyint functions (p: TBD)

• 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

rintrintfrintllrintlrintflrintlllrintllrintfllrintl (C99)(C99)(C99)(C99)(C99)(C99)(C99)(C99)(C99)	rounds to an integer using current rounding mode with exception if the result differs (function)
roundroundfroundllroundlroundflroundlllroundllroundfllroundl (C99)(C99)(C99)(C99)(C99)(C99)(C99)(C99)(C99)	rounds to nearest integer, rounding away from zero in halfway cases (function)
fegetroundfesetround (C99)(C99)	gets or sets rounding direction (function)
C++ documentation for nearbyint