FE_UNDERFLOW
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| Defined in header | | |
|---|---|---|
| #define FE_DIVBYZERO /*implementation defined power of 2*/ | | (since C++11) |
| #define FE_INEXACT /*implementation defined power of 2*/ | | (since C++11) |
| #define FE_INVALID /*implementation defined power of 2*/ | | (since C++11) |
| #define FE_OVERFLOW /*implementation defined power of 2*/ | | (since C++11) |
| #define FE_UNDERFLOW /*implementation defined power of 2*/ | | (since C++11) |
| #define FE_ALL_EXCEPT FE_DIVBYZERO | FE_INEXACT | \ FE_INVALID | FE_OVERFLOW | \ FE_UNDERFLOW | | (since C++11) |
所有这些宏常数%28除外FE_ALL_EXCEPT%29扩展为整数常量表达式，它是2的不同幂，它唯一地标识所有支持的浮点异常。每个宏只有在支持时才定义。
宏常数FE_ALL_EXCEPT，它扩展到所有其他的按位或FE_*，如果实现不支持浮点异常，则为零。
| Constant | Explanation |
|---|---|
| FE_DIVBYZERO | pole error occurred in an earlier floating-point operation |
| FE_INEXACT | inexact result: rounding was necessary to store the result of an earlier floating-point operation |
| FE_INVALID | domain error occurred in an earlier floating-point operation |
| FE_OVERFLOW | the result of the earlier floating-point operation was too large to be representable |
| FE_UNDERFLOW | the result of the earlier floating-point operation was subnormal with a loss of precision |
| FE_ALL_EXCEPT | bitwise OR of all supported floating-point exceptions |
实现可以在<cfenv>若要标识其他浮点异常，请执行以下操作。所有这些常量都以FE_后面至少有一个大写字母。
见math_errhandling更多细节。
例
二次
#include <iostream>
#include <cfenv>
#include <cmath>
#pragma STDC FENV_ACCESS ON
volatile double zero = 0.0; // volatile not needed where FENV_ACCESS is supported
volatile double one = 1.0; // volatile not needed where FENV_ACCESS is supported
int main()
{
std::feclearexcept(FE_ALL_EXCEPT
std::cout << "1.0/0.0 = " << 1.0 / zero << '\n';
if(std::fetestexcept(FE_DIVBYZERO)) {
std::cout << "division by zero reported\n";
} else {
std::cout << "divsion by zero not reported\n";
}
std::feclearexcept(FE_ALL_EXCEPT
std::cout << "1.0/10 = " << one/10 << '\n';
if(std::fetestexcept(FE_INEXACT)) {
std::cout << "inexact result reported\n";
} else {
std::cout << "inexact result not reported\n";
}
std::feclearexcept(FE_ALL_EXCEPT
std::cout << "sqrt(-1) = " << std::sqrt(-1) << '\n';
if(std::fetestexcept(FE_INVALID)) {
std::cout << "invalid result reported\n";
} else {
std::cout << "invalid result not reported\n";
}
}
二次
产出：
二次
1.0/0.0 = inf
division by zero reported
1.0/10 = 0.1
inexact result reported
sqrt(-1) = -nan
invalid result reported
二次
另见
| math_errhandlingMATH_ERRNOMATH_ERREXCEPT (C++11)(C++11)(C++11) | defines the error handling mechanism used by the common mathematical functions (macro constant) |
|---|
浮点异常宏的C文档
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