FE_DIVBYZERO, FE_INEXACT, FE_INVALID, FE_OVERFLOW, FE_UNDERFLOW, FE_ALL_EXCEPT

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.

[edit] 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()
{
    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:

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

[edit] 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

Language
Standard Library
Type support
Dynamic memory management
Error handling
Program utilities
Date and time utilities
Strings library
Algorithms
Numerics
Input/output support
Localization support
Thread support (C11)
Atomic operations (C11)

Common mathematical functions
Floating-point environment
Complex number arithmetics
Random number generation
Type-generic math

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)