Passing vector by reference

Question

Using standard C arrays, I would carry out the following:

void do_something(int el, int **arr)
{
   *arr[0] = el;
   // do something else
}

Now, I want to replace standard array with vector, and achieve the same results here:

void do_something(int el, std::vector<int> **arr)
{
   *arr.push_front(el); // this is what the function above does
}

However, the message reads, "Expression must have class type." 

How can I do this correctly?