Question

I have a class pointer declaration:

MyClass* a;

In destruction method I have:

    if (a)
    {
        delete a;
        a= NULL;
    }

I got a problem when delete the pointer a:

Attempted to read or write protected memory. This is often an indication that other memory is corrupt.

What is the cause of the problem and how can I get rid of it?

Answer 1

With your current declaration:

MyClass* a;

a gets a random value. If you never give it a valid value later, such as:

a = new MyClass();

It will point to an unknown place in memory, quite probably not a memory area reserved for your program, and hence the error when you try to delete it.

The easiest way to avoid this problem is to give a a value when you declare it:

MyClass* a = new MyClass();

or, if you cannot give it a value when you declare it (maybe you don’t know it yet), assign it to null:

MyClass* a = 0;

By the way, you can remove the test (if (a)) from your code. delete is a no-op on a null pointer.