feupdateenv() function in C++

The feupdateenv() function in C++ first saves currently raised floating-point exceptions. It restores the floating-point environment from the given fenv_t object and then raises the exceptions which were saved previously.
Syntax:

int feupdateenv( fenv_t* envp )

Parameters: It accepts a single mandatory parameter envp which specifies the pointer to the fenv_t object that is set by an earlier call to feholdexcept or fegetenv or is equal to FE_DFL_ENV. The function also accepts a pointer of type fenv_t as its argument which holds a floating point environment previously set by using feholdexcept or fegetenv and restores that floating point environment along with the current environment.
Return Value: The function returns two kinds of value described below: 

• It returns zero on success
• It returns non-zero value on failure

Below programs illustrate the above function.
Program 1:

CPP

// C++ program to illustrate the
// feupdateenv() function
#include <bits/stdc++.h>
#pragma STDC FENV_ACCESS on

// Function to use the function
double answer(double y)
{

    // struct defined
    fenv_t trial;

    // use the function feholdexcept
    feholdexcept(&trial);

    // find log value
    y = log(y);

    // clears exception
    feclearexcept(FE_OVERFLOW | FE_DIVBYZERO);

    // call the function for success or not
    feupdateenv(&trial);
    return y;
}

int main()
{
    // It is a combination of all of
    // the possible floating-point exception
    feclearexcept(FE_ALL_EXCEPT);

    // it returns the log value
    // if it is to be found
    printf("log(0.0): %f\n", answer(0.0));

    // the function does not throws any exception
    if (!fetestexcept(FE_ALL_EXCEPT)) {
        printf("no exceptions raised");
    }
    return 0;
}

Output:

log(0.0): -inf
no exceptions raised

Program 2:

CPP

// C++ program to illustrate the
// feupdateenv() function
#include <bits/stdc++.h>
#pragma STDC FENV_ACCESS on

// Function to use the function
double answer(double y)
{

    // struct defined
    fenv_t trial;

    // use the function feholdexcept
    feholdexcept(&trial);

    // find log value
    y = log(y);

    // clears exception
    feclearexcept(FE_OVERFLOW | FE_DIVBYZERO);

    // call the function for success or not
    feupdateenv(&trial);
    return y;
}

int main()
{
    // It is a combination of all of
    // the possible floating-point exception
    feclearexcept(FE_ALL_EXCEPT);

    // it returns the log value
    // if it is to be found
    printf("log(10.0): %f\n", answer(10.0));

    // the function does not throws any exception
    if (!fetestexcept(FE_ALL_EXCEPT)) {
        printf("no exceptions raised");
    }
    else
        printf("exceptions raised");

    return 0;
}

Output:

log(10.0): 2.302585
exceptions raised