Defined in header `<fenv.h>` | ||
---|---|---|

#define FE_DIVBYZERO /*implementation defined power of 2*/ | (since C99) | |

#define FE_INEXACT /*implementation defined power of 2*/ | (since C99) | |

#define FE_INVALID /*implementation defined power of 2*/ | (since C99) | |

#define FE_OVERFLOW /*implementation defined power of 2*/ | (since C99) | |

#define FE_UNDERFLOW /*implementation defined power of 2*/ | (since C99) | |

#define FE_ALL_EXCEPT FE_DIVBYZERO | FE_INEXACT | \ FE_INVALID | FE_OVERFLOW | \ FE_UNDERFLOW | (since C99) |

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 an earlier floating-point operation was too large to be representable |

`FE_UNDERFLOW` | the result of an 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 `<fenv.h>`

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 <stdio.h> #include <math.h> #include <float.h> #include <fenv.h> #pragma STDC FENV_ACCESS ON void show_fe_exceptions(void) { printf("exceptions raised:"); if(fetestexcept(FE_DIVBYZERO)) printf(" FE_DIVBYZERO"); if(fetestexcept(FE_INEXACT)) printf(" FE_INEXACT"); if(fetestexcept(FE_INVALID)) printf(" FE_INVALID"); if(fetestexcept(FE_OVERFLOW)) printf(" FE_OVERFLOW"); if(fetestexcept(FE_UNDERFLOW)) printf(" FE_UNDERFLOW"); feclearexcept(FE_ALL_EXCEPT); printf("\n"); } int main(void) { printf("MATH_ERREXCEPT is %s\n", math_errhandling & MATH_ERREXCEPT ? "set" : "not set"); printf("0.0/0.0 = %f\n", 0.0/0.0); show_fe_exceptions(); printf("1.0/0.0 = %f\n", 1.0/0.0); show_fe_exceptions(); printf("1.0/10.0 = %f\n", 1.0/10.0); show_fe_exceptions(); printf("sqrt(-1) = %f\n", sqrt(-1)); show_fe_exceptions(); printf("DBL_MAX*2.0 = %f\n", DBL_MAX*2.0); show_fe_exceptions(); printf("nextafter(DBL_MIN/pow(2.0,52),0.0) = %.1f\n", nextafter(DBL_MIN/pow(2.0,52),0.0)); show_fe_exceptions(); }

Possible output:

MATH_ERREXCEPT is set 0.0/0.0 = nan exceptions raised: FE_INVALID 1.0/0.0 = inf exceptions raised: FE_DIVBYZERO 1.0/10.0 = 0.100000 exceptions raised: FE_INEXACT sqrt(-1) = -nan exceptions raised: FE_INVALID DBL_MAX*2.0 = inf exceptions raised: FE_INEXACT FE_OVERFLOW nextafter(DBL_MIN/pow(2.0,52),0.0) = 0.0 exceptions raised: FE_INEXACT FE_UNDERFLOW

- C11 standard (ISO/IEC 9899:2011):
- 7.6/6 Floating-point environment <fenv.h> (p: 207)
- C99 standard (ISO/IEC 9899:1999):
- 7.6/5 Floating-point environment <fenv.h> (p: 188)

(C99)(C99)(C99) | defines the error handling mechanism used by the common mathematical functions (macro constant) |

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