# FE_DIVBYZERO, FE_INEXACT, FE_INVALID, FE_OVERFLOW, FE_UNDERFLOW, FE_ALL_EXCEPT

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< c‎ | numeric‎ | fenv

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.

### Example

Run this code

    #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

### References

- 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)

### See also

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

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