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在頭文件<math.h>中定義 | ||
---|---|---|
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)arg
使用當(dāng)前舍入模式將浮點(diǎn)參數(shù)四舍五入為浮點(diǎn)格式的整數(shù)值。
4)類(lèi)型 - 通用宏:如果arg
有類(lèi)型long double
,nearbyintl
被調(diào)用。否則,如果arg
有整數(shù)類(lèi)型或類(lèi)型double
,nearbyint
則調(diào)用。否則nearbyintf
,分別稱(chēng)為。
arg | - | 浮點(diǎn)值 |
---|
arg
根據(jù)當(dāng)前舍入模式,返回最接近的整數(shù)值。
此函數(shù)不受math_errhandling中指定的任何錯(cuò)誤的影響。
如果實(shí)現(xiàn)支持IEEE浮點(diǎn)運(yùn)算(IEC 60559),
FE_INEXACT
從未被提出
如果arg
是±∞,則返回,未修改
如果arg
為±0,則返回,未修改
如果arg
是NaN,則返回NaN
之間唯一的區(qū)別nearbyint
和rint
是nearbyint
永遠(yuǎn)不會(huì)提高FE_INEXACT
。
最大的可表示浮點(diǎn)值是所有標(biāo)準(zhǔn)浮點(diǎn)格式中的精確整數(shù),因此nearbyint
不會(huì)自行溢出; 但是intmax_t
,當(dāng)存儲(chǔ)在整數(shù)變量中時(shí),結(jié)果可能會(huì)溢出任何整數(shù)類(lèi)型(包括)。
如果當(dāng)前的舍入模式是FE_TONEAREST
,這個(gè)函數(shù)甚至在一半的情況下(例如rint
,但不像round
)。
#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));}
輸出:
rounding to nearest:nearbyint(+2.3) = +2.0 nearbyint(+2.5) = +2.0 nearbyint(+3.5) = +4.0nearbyint(-2.3) = -2.0 nearbyint(-2.5) = -2.0 nearbyint(-3.5) = -4.0rounding down: nearbyint(+2.3) = +2.0 nearbyint(+2.5) = +2.0 nearbyint(+3.5) = +3.0nearbyint(-2.3) = -3.0 nearbyint(-2.5) = -3.0 nearbyint(-3.5) = -4.0nearbyint(-0.0) = -0.0nearbyint(-Inf) = -inf
C11標(biāo)準(zhǔn)(ISO / IEC 9899:2011):
7.12.9.3附近的功能(p:251-252)
7.25類(lèi)型通用數(shù)學(xué)<tgmath.h>(p:373-375)
F.10.6.3附近的函數(shù)(p:526)
C99標(biāo)準(zhǔn)(ISO / IEC 9899:1999):
7.12.9.3附近的函數(shù)(p:232)
7.22類(lèi)型通用數(shù)學(xué)<tgmath.h>(p:335-337)
F.9.6.3 nearbyint函數(shù)(p:463)