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在頭文件<math.h>中定義 | ||
---|---|---|
float nextafterf( float from, float to ); | (1) | (since C99) |
double nextafter( double from, double to ); | (2) | (since C99) |
long double nextafterl( long double from, long double to ); | (3) | (since C99) |
float nexttowardf( float from, long double to ); | (4) | (since C99) |
double nexttoward( double from, long double to ); | (5) | (since C99) |
long double nexttowardl( long double from, long double to ); | (6) | (since C99) |
Defined in header <tgmath.h> | ||
#define nextafter(from, to) | (7) | (since C99) |
#define nexttoward(from, to) | (8) | (since C99) |
1-3)首先,將兩個參數(shù)都轉(zhuǎn)換為函數(shù)的類型,然后返回下一個可表示值from
的方向to
。如果from
等于to
,to
則返回。
4-6)首先,將第一個參數(shù)轉(zhuǎn)換為函數(shù)的類型,然后返回下一個可表示值from
的方向to
。如果from
等于to
,to
則返回,轉(zhuǎn)換long double
為函數(shù)的返回類型,但不會丟失范圍或精度。
7)類型 - 通用宏:如果任何參數(shù)具有類型long double
,nextafterl
則被調(diào)用。否則,如果任何參數(shù)具有整數(shù)類型或具有類型double
,nextafter
則被調(diào)用。否則,nextafterf
被調(diào)用。
8)類型 - 通用宏:如果參數(shù)from
具有類型long double
,nexttowardl
則被調(diào)用。否則,如果from
有整數(shù)類型或類型double
,nexttoward
則調(diào)用。否則,nexttowardf
被調(diào)用。
from, to | - | 浮點值 |
---|
如果沒有錯誤發(fā)生,下一個可表示值from
的方向to
。返回。如果from
等于to
,則to
返回,轉(zhuǎn)換為函數(shù)的類型。
如果范圍誤差由于發(fā)生溢出,±HUGE_VAL
,±HUGE_VALF
,或±HUGE_VALL
被返回(與相同的符號from
)。
如果由于下溢而發(fā)生范圍錯誤,則返回正確的結(jié)果。
按照math_errhandling中的指定報告錯誤。
如果實現(xiàn)支持IEEE浮點運算(IEC 60559),
如果from
是有限的,但預期的結(jié)果是無窮大,提高FE_INEXACT
和FE_OVERFLOW
如果from
不相等to
,結(jié)果是低于正?;蛄悖瑒t引發(fā)FE_INEXACT
和FE_UNDERFLOW
在任何情況下,返回值都與當前舍入模式無關(guān)
如果是from
或者to
是NaN,則返回NaN
POSIX指定溢出和下溢條件是范圍錯誤(可能會設置錯誤)。
IEC 60559建議from
每當返回from==to
。這些函數(shù)會返回to
,這會使零之間的行為保持一致:nextafter(-0.0, +0.0)
返回+0.0
并nextafter(+0.0, -0.0)
返回–0.0
。
#include <math.h>#include <stdio.h>#include <float.h>#include <fenv.h> int main(void){ float from1 = 0, to1 = nextafterf(from1, 1); printf("The next representable float after %.2f is %.20g (%a)\n", from1, to1, to1); float from2 = 1, to2 = nextafterf(from2, 2); printf("The next representable float after %.2f is %.20f (%a)\n", from2, to2, to2); double from3 = nextafter(0.1, 0), to3 = 0.1; printf("The number 0.1 lies between two valid doubles:\n" " %.56f (%a)\nand %.55f (%a)\n", from3, from3, to3, to3); // difference between nextafter and nexttoward: long double dir = nextafterl(from1, 1); // first subnormal long double float x = nextafterf(from1, dir); // first converts dir to float, giving 0 printf("Using nextafter, next float after %.2f (%a) is %.20g (%a)\n", from1, from1, x, x); x = nexttowardf(from1, dir); printf("Using nexttoward, next float after %.2f (%a) is %.20g (%a)\n", from1, from1, x, x); // special values { #pragma STDC FENV_ACCESS ON feclearexcept(FE_ALL_EXCEPT); double from4 = DBL_MAX, to4 = nextafter(from4, INFINITY); printf("The next representable double after %.2g (%a) is %.23f (%a)\n", from4, from4, to4, to4); if(fetestexcept(FE_OVERFLOW)) puts(" raised FE_OVERFLOW"); if(fetestexcept(FE_INEXACT)) puts(" raised FE_INEXACT"); } // end FENV_ACCESS block float from5 = 0.0, to5 = nextafter(from5, -0.0); printf("nextafter(+0.0, -0.0) gives %.2g (%a)\n", to5, to5);}
輸出:
The next representable float after 0.00 is 1.4012984643248170709e-45 (0x1p-149)The next representable float after 1.00 is 1.00000011920928955078 (0x1.000002p+0)The number 0.1 lies between two valid doubles: 0.09999999999999999167332731531132594682276248931884765625 (0x1.9999999999999p-4)and 0.1000000000000000055511151231257827021181583404541015625 (0x1.999999999999ap-4)Using nextafter, next float after 0.00 (0x0p+0) is 0 (0x0p+0)Using nexttoward, next float after 0.00 (0x0p+0) is 1.4012984643248170709e-45 (0x1p-149)The next representable double after 1.8e+308 (0x1.fffffffffffffp+1023) is inf (inf) raised FE_OVERFLOW raised FE_INEXACTnextafter(+0.0, -0.0) gives -0 (-0x0p+0)
C11標準(ISO / IEC 9899:2011):
7.12.11.3 nextafter函數(shù)(p:256)
7.12.11.4 nexttoward函數(shù)(p:257)
7.25類型通用數(shù)學<tgmath.h>(p:373-375)
F.10.8.3 nextafter函數(shù)(p:529)
F.10.8.4 nexttoward函數(shù)(p:529)
C99標準(ISO / IEC 9899:1999):
7.12.11.3 nextafter函數(shù)(p:237)
7.12.11.4 nexttoward函數(shù)(p:238)
7.22類型通用數(shù)學<tgmath.h>(p:335-337)
F.9.8.3 nextafter函數(shù)(p:466)
F.9.8.4 nexttoward函數(shù)(p:466)