[TIP] Virtual Destructor

[Valmont]

I'ts been a long time ago when I posted a [TIP] for the last time. A [TIP] is a mini-tutorial that takes 5 tot 10 minutes to study.

The Virtual Destructor

Imagine code like:

BaseClass* Bc = new DerivedClass;
delete Bc;

DerivedClass is a class derived from BaseClass

Question: is DerivedClass destructor called?
Answer: to make sure it does, make the destructor of the base class virtual.
That's all there's to it.

Example code:

#include <iostream>

using namespace std;

class Base
{
public:
  /* virtual*/ ~Base()
  {
    cout<<"Base Dtor called"<<endl;
  }
};

class Derived : public Base
{
public:
  ~Derived()
  {
    cout<<"Derived Dtor called"<<endl;
  }
};

int main()
{
  Base* Bp = new Derived;
  delete Bp;

  return 0;
}

Compile it, run it.
See the output?
Only the base class destructor is called.
See the main() function? The base class pointer points to a derived class! Now you know when the virtual destructor is becoming relevant.

Now remove the comment-tags from virtual in the base class.
Compile and run it.
See the output?
Now both the destructor of the base class and the derived class are called. That's the way to go.

And that's all folks. This topic isn't close to complete, but it's a clear intro I think.

[Valmont]

And [TIP]s stay sticky for a week and remains open for comments.
Do you, the visitor have a tip? Submit it or post it. We'll make it sticky for a week. The credits will be all yours .

So what's your tip?

[DJMaze]

Maybe it's cool to explain virtual so that people understand what it realy does and why it's so important?

[Valmont]

Usually a [TIP] is more of a teaser. Why not for the next [TIP] a teaser on virtual methods? Good idea. Perhaps you'd like to write one. See if you can make it a 10-minute read or something.

[Valmont]

I have thought about your proposal. If you don't beat me to it, I'll make a virutal [TIP]. So basically your idea is a good one in my opinion.