std::nextafter
STD：：下一次，STD：：Nextttoward
| Defined in header | | |
|---|---|---|
| float nextafter( float from, float to | (1) | (since C++11) |
| double nextafter( double from, double to | (2) | (since C++11) |
| long double nextafter( long double from, long double to | (3) | (since C++11) |
| Promoted nextafter( Arithmetic from, Arithmetic to | (4) | (since C++11) |
| float nexttoward( float from, long double to | (5) | (since C++11) |
| double nexttoward( double from, long double to | (6) | (since C++11) |
| long double nexttoward( long double from, long double to | (7) | (since C++11) |
| double nexttoward( Integral from, long double to | (8) | (since C++11) |
的下一个可表示值from向…的方向to...
1-3%29from等于to，，，to会被归还。
5-7%29from等于to，，，to返回，转换为long double函数的返回类型，而不丢失范围或精度。
4%29一组重载或函数模板，用于%281-3%29中未涵盖的所有算术类型参数组合。如果有任何争论积分型，它被铸造成double.如果有任何争论long double，则返回类型Promoted也是long double，否则返回类型总是double...
8%29一组重载或接受from任何论点积分型等效于%286%29%28的参数转换为double29%。
参数
| from, to | - | floating point values |
|---|
返回值
如果没有发生错误，则下一个可表示的值from向…的方向to.被归还。如果from等号to，然后to会被归还。
如果溢出导致范围错误，±HUGE_VAL，，，±HUGE_VALF，或±HUGE_VALL返回%28，其符号与from29%。
如果由于下垫流而发生范围错误，则返回正确的结果。
错误处理
错误按数学[医]错误处理...
如果实现支持ieee浮点算法%28IEC 60559%29，
- 如果
from是有限的，但预期的结果是无穷大的。FE_INEXACT和FE_OVERFLOW
- 如果
from不等于to结果是低于正常值或者为零，FE_INEXACT和FE_UNDERFLOW
- 在任何情况下，返回的值都与当前舍入模式无关。
- 如果
from或to是南，南回来了
注记
POSIX指定溢出和下溢条件为范围错误%28 errno可设置为%29。
iec 60559建议from将在任何时候返回。from==to.这些功能返回to相反，这使得在零附近的行为保持一致：std::nextafter(-0.0, +0.0)回报+0.0和std::nextafter(+0.0, -0.0)回报–0.0...
例
二次
#include <cmath>
#include <iomanip>
#include <iostream>
#include <cfloat>
#include <cfenv>
int main()
{
float from1 = 0, to1 = std::nextafter(from1, 1.f
std::cout << "The next representable float after " << std::setprecision(20) << from1
<< " is " << to1
<< std::hexfloat << " (" << to1 << ")\n" << std::defaultfloat;
float from2 = 1, to2 = std::nextafter(from2, 2.f
std::cout << "The next representable float after " << from2 << " is " << to2
<< std::hexfloat << " (" << to2 << ")\n" << std::defaultfloat;
double from3 = std::nextafter(0.1, 0), to3 = 0.1;
std::cout << "The number 0.1 lies between two valid doubles:\n"
<< std::setprecision(56) << " " << from3
<< std::hexfloat << " (" << from3 << ')' << std::defaultfloat
<< "\nand " << to3 << std::hexfloat << " (" << to3 << ")\n"
<< std::defaultfloat << std::setprecision(20
// difference between nextafter and nexttoward:
long double dir = std::nextafter(from1, 1.0L // first subnormal long double
float x = nextafter(from1, dir // first converts dir to float, giving 0
std::cout << "With nextafter, next float after " << from1 << " is " << x << '\n';
x = std::nexttoward(from1, dir
std::cout << "With nexttoward, next float after " << from1 << " is " << x << '\n';
// special values
{
#pragma STDC FENV_ACCESS ON
std::feclearexcept(FE_ALL_EXCEPT
double from4 = DBL_MAX, to4 = std::nextafter(from4, INFINITY
std::cout << "The next representable double after " << std::setprecision(6)
<< from4 << std::hexfloat << " (" << from4 << ')'
<< std::defaultfloat << " is " << to4
<< std::hexfloat << " (" << to4 << ")\n" << std::defaultfloat;
if(std::fetestexcept(FE_OVERFLOW)) std::cout << " raised FE_OVERFLOW\n";
if(std::fetestexcept(FE_INEXACT)) std::cout << " raised FE_INEXACT\n";
} // end FENV_ACCESS block
float from5 = 0.0, to5 = std::nextafter(from5, -0.0
std::cout << "std::nextafter(+0.0, -0.0) gives " << std::fixed << to5 << '\n';
}
二次
产出：
二次
The next representable float after 0 is 1.4012984643248170709e-45 (0x1p-149)
The next representable float after 1 is 1.0000001192092895508 (0x1.000002p+0)
The number 0.1 lies between two valid doubles:
0.09999999999999999167332731531132594682276248931884765625 (0x1.9999999999999p-4)
and 0.1000000000000000055511151231257827021181583404541015625 (0x1.999999999999ap-4)
With nextafter, next float after 0 is 0
With nexttoward, next float after 0 is 1.4012984643248170709e-45
The next representable double after 1.79769e+308 (0x1.fffffffffffffp+1023) is inf (inf)
raised FE_OVERFLOW
raised FE_INEXACT
std::nextafter(+0.0, -0.0) gives -0.000000
二次
另见
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