FE_DIVBYZERO, FE_INEXACT, FE_INVALID, FE_OVERFLOW, FE_UNDERFLOW, FE_ALL_EXCEPT

< c‎ | numeric‎ | fenv
 
C
 
Numerics
 
Floating point environment
Functions
(C99)
(C99)
(C99)
(C99)(C99)
(C99)(C99)
(C99)
(C99)
(C99)
Macro constants
FE_ALL_EXCEPTFE_DIVBYZEROFE_INEXACTFE_INVALIDFE_OVERFLOWFE_UNDERFLOW
(C99)
(C99)
(C99)
 
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

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