| Defined in header <cfenv> | ||
|---|---|---|
#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) |
All these macro constants (except FE_ALL_EXCEPT) expand to integer constant expressions that are distinct powers of 2, which uniquely identify all supported floating-point exceptions. Each macro is only defined if it is supported.
The macro constant FE_ALL_EXCEPT, which expands to the bitwise OR of all other FE_*, is always defined and is zero if floating-point exceptions are not supported by the implementation.
| 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 |
The implementation may define additional macro constants in <cfenv> to identify additional floating-point exceptions. All such constants begin with FE_ followed by at least one uppercase letter.
See math_errhandling for further details.
Example
#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";
}
}Output:
1.0/0.0 = inf division by zero reported 1.0/10 = 0.1 inexact result reported sqrt(-1) = -nan invalid result reported
See also
| (C++11)(C++11)(C++11) | defines the error handling mechanism used by the common mathematical functions (macro constant) |
| C documentation for floating point exception macros | |
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