Calling a function for each variadic template argument and an array

So I have some type X:

typedef ... X;

and a template function f:

class <typename T>
void f(X& x_out, const T& arg_in);

and then a function g:

void g(const X* x_array, size_t x_array_size);

I need to write a variadic template function h that does this:

template<typename... Args>
void h(Args... args)
{
    constexpr size_t nargs = sizeof...(args); // get number of args
    X x_array[nargs]; // create X array of that size

    for (int i = 0; i < nargs; i++) // foreach arg
        f(x_array[i], args[i]); // call f (doesn't work)

    g(x_array, nargs); // call g with x_array
}

The reason it doesn't work is because you can't subscript args like that at runtime.

What is the best technique to replace the middle part of h?

And the winner is Xeo:

template<class T> X fv(const T& t) { X x; f(x,t); return x; }

template<class... Args>
void h(Args... args)
{
  X x_array[] = { fv(args)... };

  g(x_array, sizeof...(Args));
}

(Actually in my specific case I can rewrite f to return x by value rather than as an out parameter, so I don't even need fv above)