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Defined in header <math.h> | ||
float nextafterf(float from,float to); | (1) | (since C99) |
double nextafter(double from,double to); | (2) | (since C99) |
longdouble nextafterl(longdouble from,longdouble to); | (3) | (since C99) |
float nexttowardf(float from,longdouble to); | (4) | (since C99) |
double nexttoward(double from,longdouble to); | (5) | (since C99) |
longdouble nexttowardl(longdouble from,longdouble to); | (6) | (since C99) |
Defined in header <tgmath.h> | ||
#define nextafter(from, to) | (7) | (since C99) |
#define nexttoward(from, to) | (8) | (since C99) |
nextafterl is called. Otherwise, if any argument has integer type or has typedouble,nextafter is called. Otherwise,nextafterf is called.nexttowardl is called. Otherwise, iffrom has integer type or the typedouble,nexttoward is called. Otherwise,nexttowardf is called.Contents |
| from, to | - | floating-point values |
If no errors occur, the next representable value offrom in the direction ofto. is returned. Iffrom equalsto, thento is returned, converted to the type of the function.
If a range error due to overflow occurs,±HUGE_VAL,±HUGE_VALF, or±HUGE_VALL is returned (with the same sign asfrom).
If a range error occurs due to underflow, the correct result is returned.
Errors are reported as specified inmath_errhandling.
If the implementation supports IEEE floating-point arithmetic (IEC 60559),
to and the result is subnormal or zero, raisesFE_INEXACT andFE_UNDERFLOW.to is NaN, NaN is returned.POSIX specifies that the overflow and the underflow conditions are range errors (errno may be set).
IEC 60559 recommends thatfrom is returned wheneverfrom== to. These functions returnto instead, which makes the behavior around zero consistent:nextafter(-0.0, +0.0) returns+0.0 andnextafter(+0.0, -0.0) returns-0.0.
nextafter is typically implemented by manipulation of IEEE representation (glibcmusl).
#include <fenv.h>#include <float.h>#include <math.h>#include <stdio.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:longdouble dir= nextafterl(from1,1);// first subnormal long doublefloat x= nextafterf(from1, dir);// first converts dir to float, giving 0printf("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 ONfeclearexcept(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);}
Output:
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)
C++ documentation fornextafter |
