The Destructor can't cleanup the memory?

signbit

Hello, I have an unmanaged document class in my code, that looks like this

class MyDocument
{
public:
MyDocument()
{
// Initilize the dynamic structures throught call to 'new' operator
}
~MyDocument()
{
// Cleanup the code
this->CleanUp(); // When the function is called, it can't access the memory
}
bool CleanUp()
{
// Clean all the memory using 'delete' operator
}
};

Then I have a pointer to it in my Form (that is a .NET managed class, a Form object).

MyDocument *document;

Inside the Constructor of the form, I initialize the document with

this->document = new MyDocument();

The Dispose() function of the Form has the code:

if(disposing && document)
delete document;

During the lifetime of the program, several time i need to free the resouces of the document class and allocated new ones, like this:

document->CleanUp(); // Code runs alright
// allocated new resources to the document

However when I close the application (i.e. the destructor of the form runs), I get an error that CleanUp() can't access the memory (because it is not accessible, may be it has been cleaned already). Could any one please explain why I can call CleanUp() anywhere in my program and I get no error (the memory gets cleaned as expected), and I get a 'Memory Not Accessible' error when I call it from the destrcutor. (I tried to comment out the code in the destructor, and the application gets cured i.e. It produces no errors/exceptions etc. - A programmer's national anthem; "AAAAAHHHHH!!!!"

Nibu babu thomas

signbit wrote:

bool CleanUp() { // Clean all the memory using 'delete' operator }

Make sure you set all pointers to NULL after deleting them. For eg:

delete pointer;
pointer = NULL;

Nibu thomas Software Developer

signbit

Yeah, I always set the pointer to NULL after it's been deleted to avoid confusion, my code looks like:

if(NULL != pointer)
{
delete pointer;
pointer = NULL;
}

- A programmer's national anthem; "AAAAAHHHHH!!!!"

Nibu babu thomas

signbit wrote:

Yeah, I always set the pointer to NULL after it's been deleted to avoid confusion, my code looks like:

Try to debug and find out. You should find something interesting. Set a breakpoint inside CleanUp, and step through.

Nibu thomas Software Developer

signbit

Pointed Noted :) I'm trying it out... - A programmer's national anthem; "AAAAAHHHHH!!!!"

Nick_Kisialiou

Why do you need such a code? As far as I remember "delete NULL;" is a valid instruction, that is delete knows about NULL and know how to handle it. Basically, there is something similar to your "if(NULL != pointer)" within implementation of delete, so there is no need for extra one.

Johann Gerell

No need to check for NULL before deleting a pointer - it's a benign operation, as free(...) in C. -- The Blog: Bits and Pieces

Stephen Hewitt

In C++ delete NULL is a NOP - It does nothing. You don't need the if statement in the code above, the following is equivalent:

delete pointer;
pointer = NULL;

If you put the if you're checking twice and the code is longer then need be (more chance of making a mistake). Steve

signbit

Okay, Okay, but why the destructor can't cleanup? - A programmer's national anthem; "AAAAAHHHHH!!!!"

Stephen Hewitt

I can't see anything wrong - Can you provide more detail? Steve