**`fetestexcept()`** determines which of the floating-point exceptions are currently raised at any given moment during the program's execution. It is defined in the `fenv.h` header. The full list of floating-point exception macros is available [here.](https://en.cppreference.com/w/c/numeric/fenv/FE_exceptions)

>The floating-point environment is a set of flags and modes that allow us to access and modify further information regarding any floating-point exceptions that have been raised.

We have to set ` #pragma STDC FENV_ACCESS` to `ON` in order to use the 
floating-point environment in a meaningful way.

# Prototype
```C
int fetestexcept( int excepts );
```
# Parameters

* `except`: bitmask of all the exception flags to test.

# Return Value

* Bitwise `OR` of the floating-point exceptions included in the argument and the exceptions that are currently set.

Floating-point exceptions

#include<stdio.h>
#include<fenv.h>
#pragma STDC FENV_ACCESS ON

int main() {
    
    // raise FE_DIVBYZERO exception
    printf("2.0/0.0 = %f\n", 2.0/0.0);
    if(fetestexcept(FE_DIVBYZERO)) printf("FE_DIVBYZERO exception raised!\n");

}

gcc compiler

The above code shows how we can check for floating-point exceptions with `fetestexcept()`. Here, the code raises a `FE_DIVIDEBYZERO` exception because the result of the operation `2.0/0.0` is undefined.

gcc.tar.gz

What is fetestexcept in C?

fetestexcept() in C identifies which floating-point exceptions are raised, requiring the fenv.h header and #pragma STDC FENV_ACCESS set to ON.

Constant	Description
FE_DIVIDEBYZERO	Raised when the result of an earlier floating point operation is exactly infinity or negative infinity
FE_INEXACT	Raised when an the result of an earlier floating-point operation required rounding
FE_INVALID	Raised when domain error occurs
FE_OVERFLOW	Raised when the result of an earlier floating-point operation was too large to be contained
FE_UNDERFLOW	Raised when the magnitude of the result is too small to be contained
FE_ALLEXCEPT	Bitwise OR of all the above flags