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× C Standard Library


The C <fenv.h> feholdexcept() function attempts to store the current state of the floating-point environment into the fenv_t object pointed by envp. Programs calling this function shall ensure that pragma FENV_ACCESS is enabled for the call.

The floating-point environment is the set of floating-point status flags and control modes supported by the implementation (including both floating-point exceptions and the rounding direction mode).

Syntax

int fegetenv (fenv_t* envp);

Parameters

envp Specify pointer to an fenv_t object where the state of the floating-point environment is stored.

Return Value

Returns 0 if the state is successfully stored. Returns a non-zero value otherwise.

Exception

This function never throws exceptions.

Example:

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

#include <stdio.h>
#include <fenv.h>
#include <math.h>

#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";
  if(fetestexcept(FE_ALL_EXCEPT) == 0) 
    cout<<" None";
  cout<<endl;
}

void Rounding_Direction_Message(void) {
  cout<<"Current rounding method: ";
  switch(fegetround()) {
    case FE_DOWNWARD: 
      cout<<"DOWNWARD"; break;
    case FE_TONEAREST:   
      cout<<"TO-NEAREST"; break;
    case FE_TOWARDZERO:   
      cout<<"TOWARD-ZERO"; break;
    case FE_UPWARD:  
      cout<<"UPWARD"; break;
    default:
      cout<<"unknown";
  }
  cout<<endl;
}

void FE_Environment_Message(void) {
  FE_Exceptions_Message();
  Rounding_Direction_Message();
  cout<<endl;
}  

int main (){
  //creating fenv_t object
  fenv_t curr_env; 

  //displaying the current environment
  FE_Environment_Message();

  //storing the current environment
  fegetenv(&curr_env);

  //changing the current environment
  //and displaying it
  sqrt(-1);
  fesetround(FE_DOWNWARD);
  FE_Environment_Message();

  //restoring the previous environment
  //and displaying it
  fesetenv(&curr_env);
  FE_Environment_Message();

  return 0;
}

The output of the above code will be:

Exceptions raised: None
Current rounding method: TO-NEAREST

Exceptions raised: FE_INVALID
Current rounding method: DOWNWARD

Exceptions raised: None
Current rounding method: TO-NEAREST

❮ C <fenv.h> Library