math_errhandling
Defined in header <cmath> | ? | ? |
|---|---|---|
#define MATH_ERRNO 1 | ? | (since C++11) |
#define MATH_ERREXCEPT 2 | ? | (since C++11) |
#define math_errhandling /*implementation defined*/ | ? | (since C++11) |
宏常数math_errhandling展开为类型的表达式。int或者等于MATH_ERRNO，或等于MATH_ERREXCEPT，或等于按位或%28MATH_ERRNO | MATH_ERREXCEPT29%。
价值math_errhandling指示由浮点运算符和功能*
Constant | Explanation |
|---|---|
MATH_ERREXCEPT | indicates that floating-point exceptions are used: at least FE_DIVBYZERO, FE_INVALID, and FE_OVERFLOW are defined in <cfenv>. |
MATH_ERRNO | indicates that floating-point operations use the variable errno to report errors. |
如果实现支持ieee浮点算法%28IEC 60559%29，math_errhandling & MATH_ERREXCEPT必须是非零的。
下列浮点错误条件已被识别：
Condition | Explanation | errno | floating-point exception | Example |
|---|---|---|---|---|
Domain error | the argument is outside the range in which the operation is mathematically defined (the description of each function lists the required domain errors) | EDOM | FE_INVALID | std::acos(2) |
Pole error | the mathematical result of the function is exactly infinite or undefined | ERANGE | FE_DIVBYZERO | std::log(0.0), 1.0/0.0 |
Range error due to overflow | the mathematical result is finite, but becomes infinite after rounding, or becomes the largest representable finite value after rounding down | ERANGE | FE_OVERFLOW | std::pow(DBL_MAX,2) |
Range error due to underflow | the result is non-zero, but becomes zero after rounding, or becomes subnormal with a loss of precision | ERANGE or unchanged (implementation-defined) | FE_UNDERFLOW or nothing (implementation-defined) | DBL_MIN/2 |
Inexact result | the result has to be rounded to fit in the destination type | unchanged | FE_INEXACT or nothing (unspecified) | std::sqrt(2), 1.0/10.0 |
注记
是否FE_INEXACT是由数学库函数引发的，一般未指定，但可以在函数%28的说明中显式指定。std::rintVSstd::nearbyint29%。
在C++11之前，没有指定浮点异常，EDOM任何域错误都是必需的，ERANGE为溢流和执行所需---对资金流动的定义。
例
二次
#include <iostream>
#include <cfenv>
#include <cmath>
#include <cerrno>
#include <cstring>
#pragma STDC FENV_ACCESS ON
int main()
{
std::cout << "MATH_ERRNO is "
<< (math_errhandling & MATH_ERRNO ? "set" : "not set") << '\n'
<< "MATH_ERREXCEPT is "
<< (math_errhandling & MATH_ERREXCEPT ? "set" : "not set") << '\n';
std::feclearexcept(FE_ALL_EXCEPT);
errno = 0;
std::cout << "log(0) = " << std::log(0) << '\n';
if(errno == ERANGE)
std::cout << "errno = ERANGE (" << std::strerror(errno) << ")\n";
if(std::fetestexcept(FE_DIVBYZERO))
std::cout << "FE_DIVBYZERO (pole error) reported\n";
}二次
可能的产出：
二次
MATH_ERRNO is set
MATH_ERREXCEPT is set
log(0) = -inf
errno = ERANGE (Numerical result out of range)
FE_DIVBYZERO (pole error) reported二次
另见
FE_ALL_EXCEPTFE_DIVBYZEROFE_INEXACTFE_INVALIDFE_OVERFLOWFE_UNDERFLOW (C++11) | floating-point exceptions (macro constant) |
|---|---|
errno | macro which expands to POSIX-compatible thread-local error number variable(macro variable) |
C数学文档[医]错误处理
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