C library - fegetenv() function

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The C fenv library fegetenv() function sets the control flow of numbers with decimal values.

Imagine we are working on a math problem and we are using a calculator that can round numbers in different ways. Though, we need to switch to a different calculator with different rounding settings. So, this function is like saving the state of your first calculator and we can go back to it later and continue with the exact same settings as before.

Syntax

Following is the C library syntax of the fegetenv() function.

int fegetenv(fenv_t *envp);

Parameters

This function accepts only a single parameter −

• fen_v - The function takes a pointer to an fenv_t object where the current environment will be stored.

Return Value

This function returns the integers value which is,

• zero, if it is succesful.

• non-zero, when the environment cannot be obtained.

Example 1

Following is the C library fegetenv() function demonstrates the task of saving and restoring of Floating-Point Environment.

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

int main() {
   fenv_t env;
   
   // Save the current floating-point environment
   fegetenv(&env); 
   
   // Perform some floating-point operations here
   fesetenv(&env); 
   
   // Restore the saved environment
   printf("Floating-point environment restored.\n");
   return 0;
}

Output

The above code produces the following result −

Floating-point environment restored.

Example 2

In this example, the program perform the operations which may cause an overflow, restore the environment and it will check whether an overflow has occured or not.

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

// rounding direction mode 
void rounding_mode() 
{ 
   printf("Rounding mode is ->");
   switch (fegetround()) { 
   case FE_TONEAREST: 
     // Round to nearest 
     printf("FE_TONEAREST\n"); 
     break; 
   case FE_DOWNWARD: 
     // Round downward 
     printf("FE_DOWNWARD\n"); 
     break; 
   case FE_UPWARD: 
     // Round upward 
     printf("FE_UPWARD\n"); 
     break; 
   case FE_TOWARDZERO: 
     // Round toward zero 
     printf("FE_TOWARDZERO\n"); 
     break; 
   default: 
     printf("unknown\n"); 
   }; 
} 

int main(void) 
{ 
    fenv_t envp; 

    // initial environment 
    printf("Initial environment :\n"); 

    // print the exception raised initially 
    printf("Exception raised -> \n"); 
    if (fetestexcept(FE_ALL_EXCEPT)) { 
        if (fetestexcept(FE_DIVBYZERO)) 
            printf("FE_DIVBYZERO \n"); 
        if (fetestexcept(FE_INEXACT)) 
            printf("FE_INEXACT \n"); 
        if (fetestexcept(FE_INVALID)) 
            printf("FE_INVALID \n"); 
        if (fetestexcept(FE_OVERFLOW)) 
            printf("FE_OVERFLOW \n"); 
        if (fetestexcept(FE_UNDERFLOW)) 
            printf("FE_UNDERFLOW \n"); 
    } 
    else
        printf("None\n"); 

    // print the rounding direction mode 
    rounding_mode(); 

    // Current environment 
    fegetenv(&envp); 
    feraiseexcept(FE_ALL_EXCEPT); 

    // Set rounding direction mode 
    fesetround(FE_DOWNWARD); 

    // after environment is change 
    printf("\nFinal environment :\n"); 

    // print the exception raised 
    printf("Exception raised -> \n"); 
    if (fetestexcept(FE_ALL_EXCEPT)) { 
        if (fetestexcept(FE_DIVBYZERO)) 
            printf("FE_DIVBYZERO \n"); 
        if (fetestexcept(FE_INEXACT)) 
            printf("FE_INEXACT \n"); 
        if (fetestexcept(FE_INVALID)) 
            printf("FE_INVALID \n"); 
        if (fetestexcept(FE_OVERFLOW)) 
            printf("FE_OVERFLOW \n"); 
        if (fetestexcept(FE_UNDERFLOW)) 
            printf("FE_UNDERFLOW \n"); 
    } 
    else
        printf("None\n"); 

    // print the rounding direction mode 
    rounding_mode(); 

    return 0; 
}

Output

On execution of above code, we get the following result −

Initial environment :
Exception raised -> 
None
Rounding mode is ->FE_TONEAREST

Final environment :
Exception raised -> 
FE_DIVBYZERO 
FE_INEXACT 
FE_INVALID 
FE_OVERFLOW 
FE_UNDERFLOW 
Rounding mode is ->FE_DOWNWARD