I read one book and ran into such a code:

class command
{
Public:
 Virtual ~ COMMAND () {}
 Virtual Void Execute (GameActor & Amp; Actor) = 0;
};

Explain why you need a virtual destructor? If I do not write it, then there will be any problems?

Answer 1, Authority 100%

The virtual destructor is necessary to avoid possible resource leaks or other uncontrolled object behavior, in which the destructor call is included.

# include & lt; iostream & gt;
Using Namespace STD;
Struct Base.
{
  Base () {cout & lt; & lt; "Base ()" & lt; & lt; Endl; }
  ~ Base () {cout & lt; & lt; "~ BASE ()" & lt; & lt; Endl; }
};
Struct Derived: Public Base
{
  Derived () {cout & lt; & lt; "Derived ()" & lt; & lt; Endl; }
  ~ Derived () {cout & lt; & lt; "~ Derived ()" & lt; & lt; Endl; }
};
INT MAIN ()
{
  Base * OBJ = new DERIED ();
  Delete OBJ;
}

What could you expect at the exit:

base ()
DERIVED ()
~ Derived ()
~ Base ()

What can happen (maybe because, in general, it is Undefined Behaviour ):

base ()
DERIVED ()
~ Base ()

To eliminate this problem, a parent class destructor is needed to announce virtual (Virtual ~ Base () ), which will allow the compiler to get to the destructor of the heir on the virtual feature table.