What is fegetexceptflag() in C?

fegetexceptflag() attempts to store all the currently raised exceptions included in the excepts in an object pointed to by the flag_p pointer. It is defined in the fenv.h header.

Prototype

int fegetexceptflag( fexcept_t* flagp, int excepts );

Parameters

flagp: A pointer of type fexcept_t that points to the object where the floating-point exceptions will be saved.
excepts: A bitmask consisting of the bitwise OR of all the floating-point exceptions that need to be saved.

Return value

fegetexceptflag() returns $0$ on success; otherwise, it returns a non-zero value.

Example

#include<stdio.h>
#include <math.h>
#include <fenv.h>
void raise_exceptions(){
    feraiseexcept(FE_OVERFLOW); 
    feraiseexcept(FE_INEXACT); 
}
void display_raised_exceptions(){
    printf("Currently raised exceptions are: ");
    if (fetestexcept(FE_DIVBYZERO)) printf("FE_DIVBYZERO ");
    if (fetestexcept(FE_INVALID)) printf("FE_INVALID ");
    if (fetestexcept(FE_INEXACT)) printf("FE_INEXACT ");
    if (fetestexcept(FE_UNDERFLOW)) printf("FE_UNDERFLOW ");
    if (fetestexcept(FE_OVERFLOW)) printf("FE_OVERFLOW ");
    if (!fetestexcept(FE_ALL_EXCEPT)) printf("NONE ");
    printf("\n");
}
int main() {
    fexcept_t excepts;
    raise_exceptions();
    display_raised_exceptions();
    fegetexceptflag(&excepts, FE_ALL_EXCEPT);
    printf("CLEARING ALL EXCEPTIONS...\n");
    feclearexcept(FE_ALL_EXCEPT);
    display_raised_exceptions();
    printf("RESTORING STORED EXCEPTIONS...\n");
    fesetexceptflag(&excepts, FE_ALL_EXCEPT);
    display_raised_exceptions();
}

We initialize a variable of type fexcept_t called excepts, which we will use to store the floating-point exceptions.

In the function raise_exceptions(), we use feraiseexccept() to raise the floating-point exceptions of our choice.

We store these exceptions in the variable excepts and then clear all exceptions using:

feclearexcept(FE_ALL_EXCEPT);

Then, we restore the exceptions using the fesetexceptflag() function. The output will show that all of the exceptions that were stored in excepts have been raised.

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