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.

#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

(C++11)(C++11)(C++11) | defines the error handling mechanism used by the common mathematical functions (macro constant) |

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