How to delete the Base class pointer?

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This is mine whole code.......

C++

class Interface
{
public:
virtual void fun()=0;
};
class Derived:public Interface
{
public:
void fun()
{
printf("i am in derived class fun\n");
}
};

int main()
{
Interface *pInterface;
Derived obj_Derived;

pInterface=&obj_Derived;

pInterface->fun();


return 0;
}

I want to delete the

pInterface pointer

so can i call

delete pInterface;

or should i have to take virtual destructor in Interface class.

Posted 1-Nov-12 20:40pm

Tarun Batra

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3 solutions

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ayguen · Answer 1 · 2012-11-01T22:41:00

Solution 2

Virtual destructor would be a good idea, BUT your main example does NOT need any delete!, cause obj_Derived is instanciated on stack.

When changing the example to

C#

int main()
{
  Interface *pInterface;

  pInterface=new Derived();
  pInterface->fun();

  delete pInterface;
  return 0;
}

THEN the virtual destructor will do the job.

Posted 1-Nov-12 22:41pm

ayguen

Comments

nv3 2-Nov-12 5:59am

Good point!

Eugen Podsypalnikov 2-Nov-12 6:42am

Good point for a classical base class,
not for the interfaces, which are nomally defined to hide the objects behind them :)

[no name] 2-Nov-12 8:42am

ayguen explained well. good

nv3 · Answer 2 · 2012-11-01T21:22:00

Solution 1

You guessed correctly:

C++

delete pInterface;

will not do the job, because the compiler has no idea about which object is going to be deleted by this. So declare a virtual destructor in your interface class and all will be fine.

Posted 1-Nov-12 21:22pm

nv3

Comments

Tarun Batra 2-Nov-12 3:31am

is it like this:-
class Interface
{
public:
virtual void fun()=0;
virtual ~Interface();
};
class Derived:public Interface
{
public:
virtual ~Derived();
void fun()
{
printf("i am in derived class fun\n");
}
};

Tarun Batra 2-Nov-12 3:45am

it should be :-
class Interface { public: virtual void fun()=0; virtual ~Interface(){} }; class Derived:public Interface { public: ~Derived(){} void fun() { printf("i am in derived class fun\n"); } };

nv3 2-Nov-12 4:11am

Looks good to me. Now, if you are running Visual Studio then try both versions, with and without the virtual destructor and watch how the version without virtual destructor reports a memory leak at the end of your run. You need to add some dummy member variables to your derived class for this test, so that the derived object is really larger than the base class object.

Lesson to learn: Whenever you plan on deriving from a class, give it a virtual destructor.

Eugen Podsypalnikov · Answer 3 · 2012-11-02T00:05:00

Solution 3

// I want to delete the pInterface
Why ? There was no new for it... :)

Posted 2-Nov-12 0:05am

Eugen Podsypalnikov