C++ <cfenv> - FE_INEXACT

The FE_INEXACT macro expands to a value of type integer constant expression that is distinct powers of 2, which uniquely identifies the floating-point exception raised on inexact results.

Inexact exceptions are raised when the return type of an operation cannot represent the result with exact accuracy (for example - 1.0/3.0 or sqrt(2.0) on most implementations), or when a function cannot produce an exact result for some other reason.

Definition in the <cfenv> header file is:

C++11

#define FE_INEXACT  /*implementation defined power of 2*/

The details about all floating-point exception macros are listed below:

Macros	Description
FE_DIVBYZERO	Pole error exception occurred in an earlier floating-point operation.
FE_INEXACT	Inexact result exception occurred in an earlier floating-point operation (rounding was necessary to store the result).
FE_INVALID	Invalid argument exception occurred (domain error occurred) in an earlier floating-point operation.
FE_OVERFLOW	Overflow range error exception occurred in an earlier floating-point operation (result was too large to be representable).
FE_UNDERFLOW	Underflow range error exception occurred in an earlier floating-point operation (result was subnormal with a loss of precision).
FE_ALL_EXCEPT	Bitwise OR of all supported floating-point exceptions.

Certain library implementations may define additional macro constants in <cfenv> to identify additional floating-point exceptions (with their corresponding macros also beginning with FE_).

See math_errhandling for more details.

Example:

The example below shows the usage of FE_INEXACT macro.

#include <iostream>
#include <cfenv>

#pragma STDC FENV_ACCESS ON

//volatile not needed if FENV_ACCESS is supported
volatile double three = 3.0; 

using namespace std;
 
int main (){
  cout<<"1.0/3.0 = "<<(1.0/three)<<"\n";
  if(fetestexcept(FE_INEXACT))
    cout<<"Inexact result is reported.\n";
  else
    cout<<"Inexact result is not reported.\n";

  return 0;
}

The output of the above code will be:

1.0/3.0 = 0.333333
Inexact result is reported.

❮ C++ <cfenv> Library