C++ <cfenv> - fesetexceptflag() Function

The C++ <cfenv> fesetexceptflag() function attempts to set the floating-point exception flags indicated by excepts with the states stored in the fexcept_t object pointed by flagp. Programs calling this function shall ensure that pragma FENV_ACCESS is enabled for the call.

If successful, the function changes the current state of the floating-point environment, setting the requested exception flags, but without actually raising the exceptions.

Syntax

C++11

int fesetexceptflag (const fexcept_t* flagp, int excepts);

Parameters

flagp Specify pointer to an fexcept_t object from where the flags will be read.

excepts

Specify bitmask listing the floating-point exception flags to set.

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_).

Return Value

Returns 0 if the flags are successfully set. Returns a non-zero value otherwise.

Exception

This function never throws exceptions.

Example:

The example below shows the usage of fesetexceptflag() function.

#include <iostream>
#include <cfenv>
#include <cmath>

#pragma STDC FENV_ACCESS ON

using namespace std;

void FE_Exceptions_Message(void) {
  cout<<"Exceptions raised:";
  if(fetestexcept(FE_DIVBYZERO)) 
    cout<<" FE_DIVBYZERO";
  if(fetestexcept(FE_INEXACT))   
    cout<<" FE_INEXACT";
  if(fetestexcept(FE_INVALID))   
    cout<<" FE_INVALID";
  if(fetestexcept(FE_OVERFLOW))  
    cout<<" FE_OVERFLOW";
  if(fetestexcept(FE_UNDERFLOW)) 
    cout<<" FE_UNDERFLOW";
  cout<<endl;
}

int main (){
  //creating fexcept_t object
  fexcept_t excepts; 

  //raising FE_DIVBYZERO exception
  feraiseexcept(FE_DIVBYZERO);
  FE_Exceptions_Message();

  //storing current exception flag
  fegetexceptflag(&excepts,FE_ALL_EXCEPT);

  //clear previous exception flag and 
  //create another exception flags
  feclearexcept(FE_ALL_EXCEPT);
  feraiseexcept(FE_INVALID | FE_INEXACT);
  FE_Exceptions_Message();

  //restoring previous exception flags
  fesetexceptflag(&excepts,FE_ALL_EXCEPT);
  FE_Exceptions_Message();

  return 0;
}

The output of the above code will be:

Exceptions raised: FE_DIVBYZERO
Exceptions raised: FE_INEXACT FE_INVALID
Exceptions raised: FE_DIVBYZERO

❮ C++ <cfenv> Library