delete pointers, VC++, Debug Assertion Failled

[loisir1976]

Hello!
I am having the error "Debug Assertion Failed" at the run time with the code below. I compiled the code with MVC++ 2010, in debug mode when I click on retry on the error window it direct me to the file dbgdel.cpp at the line

_ASSERTE(_BLOCK_TYPE_IS_VALID(pHead->nBlockUse));

When I comment in the code the line

delete result;

/* code */
The error disappears... I would appreciate your help to understand the problem. Sould I delete the pointer result, new is used to created with clone method
(Sorry I can't post the full code and it is too big)

Thanks for your help

########

File: DrawShapeBase.cpp 
...
...

Base* DrawShapeBase::SetOutput(Base* input)
{
   return (input->clone());
}


....
Base* DrawShapeBase::Draw(Base* data){
	Base* result = setOuput(data); 
        ...
	...
	return result; 

}

##############
File: Derived.cpp

...
...

Base* Derived::clone()
{
    Base* b = new Derived(*this);
    return b;
}

...
...
##############
File Base.h
public:
  
	Base();
  
	~Base();

  
  
	virtual Base* clone(void) = 0;
....


############
main.cpp 


...
...
Base* data = new Derived();
DrawBase* dr = new DrawShapeBase();
Base* result = dr->Draw(data);

delete data;
delete result;
delete dr; 
...

[ne555]

> Sorry I can't post the full code and it is too big
Try to create a minimal example.
At least post relevant parts

[Disch]

Base* result = dr->Draw(data);

delete data;
delete result;

Doesn't look like result was created with new. Why are you deleting it?

Unless Draw() returns a new'd pointer... but that seems extremely goofy if that's really what it does.

Did you mean to delete 'dr' instead of 'result'?


EDIT: also, use smart pointers to save yourself these kinds of headaches

[KRAkatau]

Is the destructor of Base declared virtual?

[loisir1976]

Thanks for the replies!

@Disch you are right, Draw() uses a clone method that return a new pointer and then process the data and finally returns the pointer.

I use delete for dr, data, (both are 'new' pointers) and result, but it is the delete of result that cuase the problem.

@KRAkatau the destructor of Base is declared like this:
~Base();
Is it a problem?


@ne555 I added here more details

########

File: DrawShapeBase.cpp 
...
...

Base* DrawShapeBase::SetOutput(Base* input)
{
   return (input->clone());
}


....
Base* DrawShapeBase::Draw(Base* data){
	Base* result = setOuput(data); 
        ...
	...
	return result; 

}

##############
File: Derived.cpp

...
...

Base* Derived::clone()
{
    Base* b = new Derived(*this);
    return b;
}

...
...
##############
File Base.h
public:
  
	Base();
  
	~Base();

  
  
	virtual Base* clone(void) = 0;
....


############
main.cpp 


...
...
Base* data = new Derived();
DrawBase* dr = new DrawShapeBase();
Base* result = dr->Draw(data);

delete data;
delete result;
delete dr; 
...

Thanks

[loisir1976]

Hello!

I updated the code: added more details, I hope that it will help

[KRAkatau]

Yes, this is the problem. When you delete an object by pointer to a base class, in order for correct destructor to be called, the base-class destructor should be declared as virtual: virtual ~Base();

Most likely this causes your debug assertion. In Release production code this might lead to either memory leak or a crash.

[loisir1976]

@KRAkatou I have put in the classes that contains virtual functions virtual destructors (virtual ~class_name()) but I still getting the same error...

[S G H]

Use smart pointers, as suggested above.
This will solve most of the problems, if not all, and also helps you building better programs in an easier way.

[loisir1976]

@EssGeEich I will use smart pointers but I would like first to make this code works

[ne555]

> I use delete for dr, data, (both are 'new' pointers) and result,
¿is there something that you don't new/delete?
You do know that you can declare objects, ¿right?

Again, try to create a minimal example that does reproduce your issue.