FE_DIVBYZERO, FE_INEXACT, FE_INVALID, FE_OVERFLOW, FE_UNDERFLOW, FE_ALL_EXCEPT

 

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Floating-point environment

Functions

feclearexcept (C++11)

fetestexcept (C++11)

feraiseexcept (C++11)

fegetexceptflagfesetexceptflag (C++11)(C++11)

fegetroundfesetround (C++11)(C++11)

fegetenvfesetenv (C++11)(C++11)

feholdexcept (C++11)

feupdateenv (C++11)

Macro constants

FE_ALL_EXCEPTFE_DIVBYZEROFE_INEXACTFE_INVALIDFE_OVERFLOWFE_UNDERFLOW (C++11)(C++11)(C++11)(C++11)(C++11)(C++11)

FE_DOWNWARDFE_TONEARESTFE_TOWARDZEROFE_UPWARD (C++11)(C++11)(C++11)(C++11)

FE_DFL_ENV (C++11)

 

Defined in header <cfenv>
#define FE_DIVBYZERO    /*implementation defined power of 2*/		(since C++11)
#define FE_INEXACT      /*implementation defined power of 2*/		(since C++11)
#define FE_INVALID      /*implementation defined power of 2*/		(since C++11)
#define FE_OVERFLOW     /*implementation defined power of 2*/		(since C++11)
#define FE_UNDERFLOW    /*implementation defined power of 2*/		(since C++11)
#define FE_ALL_EXCEPT   FE_DIVBYZERO | FE_INEXACT | \                         FE_INVALID | FE_OVERFLOW |  \                         FE_UNDERFLOW		(since C++11)

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 defined only 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 the earlier floating-point operation was too large to be representable
FE_UNDERFLOW	the result of the 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 <cfenv> 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 <cfenv>
#include <cmath>
#include <iostream>
 
// #pragma STDC FENV_ACCESS ON
 
volatile double zero = 0.0; // volatile not needed where FENV_ACCESS is supported
volatile double one = 1.0;  // volatile not needed where FENV_ACCESS is supported
 
int main()
{
    std::feclearexcept(FE_ALL_EXCEPT);
    std::cout <<  "1.0/0.0 = " << 1.0 / zero << '\n';
    if (std::fetestexcept(FE_DIVBYZERO))
        std::cout << "division by zero reported\n";
    else
        std::cout << "division by zero not reported\n";
 
    std::feclearexcept(FE_ALL_EXCEPT);
    std::cout << "1.0/10 = " << one / 10 << '\n';
    if (std::fetestexcept(FE_INEXACT))
        std::cout << "inexact result reported\n";
    else
        std::cout << "inexact result not reported\n";
 
    std::feclearexcept(FE_ALL_EXCEPT);
    std::cout << "sqrt(-1) = " << std::sqrt(-1) << '\n';
    if (std::fetestexcept(FE_INVALID))
        std::cout << "invalid result reported\n";
    else
        std::cout << "invalid result not reported\n";
}

Possible output:

1.0/0.0 = inf
division by zero reported
1.0/10 = 0.1
inexact result reported
sqrt(-1) = -nan
invalid result reported

See also

math_errhandlingMATH_ERRNOMATH_ERREXCEPT (C++11)(C++11)(C++11)	defines the error handling mechanism used by the common mathematical functions (macro constant)
C documentation for floating point exception macros