FE_DIVBYZERO, FE_INEXACT, FE_INVALID, FE_OVERFLOW, FE_UNDERFLOW, FE_ALL_EXCEPT

 

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Technical Specifications

Symbol index

 

Numerics

Common mathematical functions

Floating-point environment (C99)

Pseudo-random number generation

Complex number arithmetic (C99)

Type-generic math (C99)

 

Floating-point environment

Functions

feclearexcept (C99)

fetestexcept (C99)

feraiseexcept (C99)

fegetexceptflagfesetexceptflag (C99)(C99)

fegetroundfesetround (C99)(C99)

fegetenvfesetenv (C99)

feholdexcept (C99)

feupdateenv (C99)

Macro constants

FE_ALL_EXCEPTFE_DIVBYZEROFE_INEXACTFE_INVALIDFE_OVERFLOWFE_UNDERFLOW (C99)

FE_DOWNWARDFE_TONEARESTFE_TOWARDZEROFE_UPWARD (C99)

FE_DFL_ENV (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

math_errhandlingMATH_ERRNOMATH_ERREXCEPT (C99)(C99)(C99)	defines the error handling mechanism used by the common mathematical functions (macro constant)
C++ documentation for floating-point exception macros