Double freeing of freed memory

[majesticmanish]

Hi, I am newbie in C++. In a C++ Program, i am getting error message as "Double freeing of freed memory may be in class 'WSO'. copy constructor and operator= is not defined." I haven't defined any copy-constructor and operator overloading in Class 'WSO' (since i haven't use any assignment or copying object sort of things). Private member function of Class CNN uses a object pointer of another class 'NSA'. I used copy-constructor for this calss 'NSA'.

So my question is what could be the possibility of double freeing the memory.

destructor of Class 'WSO' just deletes pointer member of class 'NSA'.

[dewyatt]

I believe your compiler is warning you because you are using heap-allocated (new'ed) data in your class and haven't defined operator= .
It could be that it isn't even heap-allocated memory, it could be a pointer to anything but your compiler probably doesn't realize this.

The compiler will create operator= for you but it will perform a shallow copy, not a deep copy.
In other words it will copy the pointer address of the data, it will not re-allocate space and copy the new'ed data.

An example:

#include <iostream>

class Test
{
	public:

	Test()
	{
		myData = new int;
		printf("Created data: 0x%08X\n", myData);
	}

	~Test()
	{
		printf("Destroying data: 0x%08X\n", myData);
		delete myData;
	}

	private:
	int* myData;
};

int main(int argc, char* argv[])
{
	Test test1;
	Test test2;

	test2 = test1;

	Test test3(test1);
}

This will produce output similar to:

Created data: 0x00333FC8
Created data: 0x00333148
Destroying data: 0x00333FC8
Destroying data: 0x00333FC8
Destroying data: 0x00333FC8

As you can see, this leaks memory (test2's data, 0x00333148), and triple-frees memory (0x00333FC8).

[majesticmanish]

thanks for explanation through coding.

[dewyatt]

No problem.
If there's anything you didn't understand, let me know!