Confusion on virtual functions declaration and definition
<p>These are some concern I have since when I understand how to use and what to use virtual functions for.</p>

<p>First, online, I've seen many styles for declaring virtual functions. While <code>virtual</code> is <em>always</em> (obviously) written in the base class's virtual function declaration, the derived class's declaration is sometimes declared with <code>virtual</code>, sometimes with <code>override</code>, sometimes with both, sometimes with neither. What is the correct style?</p>

<p>Second, if I have a virtual function in the base class, but in one of the derived classes I don't want to make that function usable, how do I do it?</p>

<p>Third, do I have to put <code>virtual</code> in the function definition (in the .cpp file)?</p>