Memory Container on Extended Pointer Leak

SamNainocard · 08-09-2015 02:29 PM

Hi, I'm have a problem with memory leak when using Memory Container inside extended class, that have another class have a pointer that pointed to Base class, and when every create a new element it will leak, however it will leak only once.

Here's example

Code:

/******************************************************************************/

class TEST : BASE_CLASS

{

   Memx<int> mem2;

   virtual void add(){mem2.New()=0;}

}

class BASE_CLASS

{

   //Memx<int> mem1;

   virtual void add(){/*mem1.New()=0;*/}

}

class POINTER

{

   BASE_CLASS * t=null;

   ~POINTER() {delete t;}

}

POINTER test1,

        test2;

/******************************************************************************/

void InitPre()

{

   App.flag=APP_MEM_LEAKS;

   EE_INIT();

}

/******************************************************************************/

bool Init()

{

   test1.t=new BASE_CLASS();

   test2.t=new TEST();

   test1.t.add();  // Not Leak

   test1.t.add();

   test2.t.add();  // Leak

   test2.t.add();

   return true;

}

/******************************************************************************/

void Shut()

{

}

/******************************************************************************/

bool Update()

{

   if(Kb.bp(KB_ESC))return false;

   return true;

}

/******************************************************************************/

void Draw() // main drawing

{

   D.clear(TURQ);

   D.text (0, 0, "Hello to Esenthel Engine !");

}

/******************************************************************************/

Once create new element, test2 will leak for 3 (2 for Memb, 1 for Memc) even with additional element or clear before delete.

How do I fix this?

Thank you in advance. smile

Zervox · 08-09-2015 02:33 PM

try adding virtual ~BASE_CLASS

SamNainocard · 08-09-2015 03:16 PM

Sorry, but what should I put into ~BASE_CLASS()?

By the way, I forget that 'mem1' doesn't leak, so I'll comment 'mem1' from code.

Zervox · 08-09-2015 03:35 PM

nwm, forum wasn't displaying properly.

BASE_CLASS * t=null;
~POINTER() {delete t;}

in this case you really should be doing

Code:

if(t){

 delete t;

 t=nullptr;

}

you shouldn't need to add anything to the virtual ~BASE, this is just to make sure that the higher object makes sure to call destruction every level.

without the virtual destructor it will not destruct the class that extends it, hence both class destructors needs to be declared.

Code:

struct TestA{

    virtual ~TestA(){}

};

struct TestB : TestA

    virtual ~TestB(){}

};

See if that doesn't help

http://stackoverflow.com/questions/46120...estructors
This link explains what is going on.

SamNainocard · 08-09-2015 05:19 PM

Oh, I forget to add "virtual", now adding "virtual ~BASE_CLASS()" does fix the problem, I never know about virtual deconstructor.

TYVM. smile

rstralberg · 08-09-2015 07:33 PM

I would say that one should always use virtual for destructors as you never know if anyone will inherit your class. I really cant see any case where you shouldn't have a virtual destructor, at least if something is done in your destructor.

Zervox · 08-10-2015 05:16 AM

(08-09-2015 07:33 PM)rstralberg Wrote: I would say that one should always use virtual for destructors as you never know if anyone will inherit your class. I really cant see any case where you shouldn't have a virtual destructor, at least if something is done in your destructor.

Actually, you shouldn't make everything use virtual destructor or virtual functions for that matter, it's a waste of performance.
You should only use virtual destructors when you deal with code that you only keep in base classes that will delete an object through a non extending pointer like Sam does in this example.

rstralberg · 08-10-2015 07:15 AM

(08-10-2015 05:16 AM)Zervox Wrote:
(08-09-2015 07:33 PM)rstralberg Wrote: I would say that one should always use virtual for destructors as you never know if anyone will inherit your class. I really cant see any case where you shouldn't have a virtual destructor, at least if something is done in your destructor.

Actually, you shouldn't make everything use virtual destructor or virtual functions for that matter, it's a waste of performance.
You should only use virtual destructors when you deal with code that you only keep in base classes that will delete an object through a non extending pointer like Sam does in this example.

Exactly. Wasn't it that what I said. I was only talking about destructors that do anything. When coming to virtual methods its a completely different thing of course. Here you should use the virtual only when its actually needed.

Zervox · 08-10-2015 07:44 AM

From what I understood you said to use virtual destructors everywhere because there is no reason not to, and I am sorry if I misunderstood you.

Virtual destructors cost performance too and is a waste if your class is not supposed to be extended.

design a class for what it is meant to do not what some other person MIGHT want it to do. if you write every class to follow the reasoning that "someone might do" you will essentially be overengineering everything and maybe loose valuable performance in the process.

It's not about destructors that do something, you need virtual destructors ONLY if a person does
Base *der=new Derived();
if it was
Derived *der=new Derived();
it doesn't need a virtual destructor as it will call Base destructor automatically.
the reason for virtual is only if you go from base to derived.

again sorry if I misunderstood.

rstralberg · 08-10-2015 07:47 AM

(08-10-2015 07:44 AM)Zervox Wrote: From what I understood you said to use virtual destructors everywhere because there is no reason not to, and I am sorry if I misunderstood you.

Virtual destructors cost performance too and is a waste if your class is not supposed to be extended.

design a class for what it is meant to do not what some other person MIGHT want it to do. if you write every class to follow the reasoning that "someone might do" you will essentially be overengineering everything and maybe loose valuable performance in the process.

It's not about destructors that do something, you need virtual destructors ONLY if a person does
Base *der=new Derived();
if it was
Derived *der=new Derived();
it doesn't need a virtual destructor as it will call Base destructor automatically.
the reason for virtual is only if you go from base to derived.

again sorry if I misunderstood.

Not a problem. You are perfectly right smile

(08-10-2015 07:44 AM)Zervox Wrote: From what I understood you said to use virtual destructors everywhere because there is no reason not to, and I am sorry if I misunderstood you.

Virtual destructors cost performance too and is a waste if your class is not supposed to be extended.

design a class for what it is meant to do not what some other person MIGHT want it to do. if you write every class to follow the reasoning that "someone might do" you will essentially be overengineering everything and maybe loose valuable performance in the process.

It's not about destructors that do something, you need virtual destructors ONLY if a person does
Base *der=new Derived();
if it was
Derived *der=new Derived();
it doesn't need a virtual destructor as it will call Base destructor automatically.
the reason for virtual is only if you go from base to derived.

again sorry if I misunderstood.

Not a problem. You are perfectly right smile

I was quite unclear and didn't think of this last case.
So there you go all. Zervox have the absolute correct solution to this.

Pixel Perfect · 08-10-2015 04:12 PM

(08-10-2015 07:44 AM)Zervox Wrote: ...
design a class for what it is meant to do not what some other person MIGHT want it to do. if you write every class to follow the reasoning that "someone might do" you will essentially be overengineering everything and maybe loose valuable performance in the process.
...

This is good advice ... I like this smile

Thanks also guys for the discussion on the use of virtual destructors, a handy reminder.

Memory Container on Extended Pointer Leak
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