# fetestexcept

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< c‎ | numeric‎ | fenv

Defined in header `<fenv.h>` |  |
int fetestexcept( int excepts ); |  | (since C99)

Determines which of the specified subset of the floating point exceptions are currently set. The argument `excepts` is a bitwise OR of the floating point exception macros.

### Parameters

excepts | - | bitmask listing the exception flags to test

### Return value

Bitwise OR of the floating-point exception macros that are both included in `excepts` and correspond to floating-point exceptions currently set.

### Example

Run this code

    #include <stdio.h>
    #include <math.h>
    #include <fenv.h>
    #include <float.h>

    #pragma STDC FENV_ACCESS ON

    void show_fe_exceptions(void)
    {
        printf("current 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");
        if(fetestexcept(FE_ALL_EXCEPT)==0) printf(" none");
        printf("\n");
    }

    int main(void)
    {
        /* Show default set of exception flags. */
        show_fe_exceptions();

        /* Perform some computations which raise exceptions. */
        printf("1.0/0.0     = %f\n", 1.0/0.0);        /* FE_DIVBYZERO            */
        printf("1.0/10.0    = %f\n", 1.0/10.0);       /* FE_INEXACT              */
        printf("sqrt(-1)    = %f\n", sqrt(-1));       /* FE_INVALID              */
        printf("DBL_MAX*2.0 = %f\n", DBL_MAX*2.0);    /* FE_INEXACT FE_OVERFLOW  */
        printf("nextafter(DBL_MIN/pow(2.0,52),0.0) = %.1f\n",
               nextafter(DBL_MIN/pow(2.0,52),0.0));   /* FE_INEXACT FE_UNDERFLOW */
        show_fe_exceptions();

        return 0;
    }

Output:

    current exceptions raised:  none
    1.0/0.0     = inf
    1.0/10.0    = 0.100000
    sqrt(-1)    = -nan
    DBL_MAX*2.0 = inf
    nextafter(DBL_MIN/pow(2.0,52),0.0) = 0.0
    current exceptions raised:  FE_DIVBYZERO FE_INEXACT FE_INVALID FE_OVERFLOW FE_UNDERFLOW

### References

- C11 standard (ISO/IEC 9899:2011):

  - 7.6.2.5 The fetestexcept function (p: 211-212)

- C99 standard (ISO/IEC 9899:1999):

  - 7.6.2.5 The fetestexcept function (p: 192-193)

### See also

feclearexcept (C99) | clears the specified floating-point status flags (function)
C++ documentation for fetestexcept

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