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C++ Best Practices ​

  1. If you use it, include it, don't depend on headers including each other.
  2. (Note that the destructor of a base class must be virtual, as is the case for all classes you intend to inherit from - otherwise the destructor of the derived class will not be called when you delete an object through a base pointer, and you’ll get corrupted program states like memory leaks.)
  3. You should make a function virtual only when there is a valid reason for a subclass to override it.

Virtual Destructors ​

Always make a base class's destructor virtual and public, or non-virtual and protected.

Example Say you create a base class Parent that has virtual methods and a derived class Child that inherits from base.

C++
class Parent {
	~Parent(){}
	// virtual methods
}

class Child : public Parent {
	~Child() {
		// clean up
	}
}
class Parent {
	~Parent(){}
	// virtual methods
}

class Child : public Parent {
	~Child() {
		// clean up
	}
}

Using the polymorphism of C++ you can create a concrete dervied class through a pointer to the base class.

C++
Parent *p = new Child();
delete p;
Parent *p = new Child();
delete p;

In this case only the destructor of Parent is called, because that's the static type. Since the destructor of Child won't be called, a memory leak can occur.

To resolve this issue, always make the base class's destructor virtual.

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