how to handle pointer to parent in copy constructor

[rssmps]

Got a question on how to write copy constructors when pointers to parent object is involved.

class File
{
private:
	vector<Data> file;
public:
	// constructor
	const CombinedData * parentSet;
	File(const string &  strin, const CombinedData * parent);
	File(const IDTSegDefFile & old);
	~File(void);
};

I have a File object that has a vector of Data obects. I need to keep track of which File each Data belongs to. So withing each Data, I've got a File pointer.

class Data
{
public:
	// constructor
	const File * parentFile;
	Data(const string & strin, const File * parent);
	Data(const Data & old);
	~Data(void);
};

I populate the data vector by this in the File constructor and pass along the this pointer so each Data can point back to the parent File obj.

File::File(const string &  strin, const CombinedData * parent)
{
    ...
    // reads data from file and creates a vector of Data obj
    file.push_back(Data(currentLineRead, this));
    ...
};

so I can see an issue when a copy constructor is used. When a copy is made, all the references point back to the original obj.

Data::Data(const Data & old):
	lac       (old.lac),
	lgc       (old.lgc),
	lstc      (old.lstc),
	name      (old.name),
	path      (old.path),
	sif       (old.sif),
	sn        (old.sn),
	ude       (old.ude),
	parentFile(old.parentFile)
{
};

let say I've got these lines of code:

File A(.... , ....);
File B(A);

when the vector in B copies A, what File obj does each Data in B.file point to?
B.file = A.file;

I would think it's still A.....because the way my Data copy constructor above is written.

What's the proper way to update the parent object? update parent pointer of each Data oject from the File copy constructor after the copy of vector is made?

File::File(const Data & old): file(old.file)
{
    for (int i=0; i<file.size(); i++)
    {
        file[i].updateParent(this);
    }    
};

in a realted question, since these pointer do not piont to objects created by new, I don't need to have delete in the destructor right? but should I have a parentFile = 0;

Thanks!

[drkybelk]

Yes,
your copied object would point to the original parent. Your implementation of the copy constructor is actually what would have been created for you anyway. And that will cause you problems, when the copied/original Data-objects are deleted, because the same memory will be attempted to be deleted twice (or multiple times). *BAD*.
I recommend you have a look at your design: I think the is the real problem here.
Probably what you really need is something like:

class File
{
...
};
class FileData
{
...
private:
    // composition: open the file,keep it open if you must and store the data here
    File theFile;
    vector<char> theData;
};

Or if the File class is a very special class that only ever will be used by the Data class you can nest it into the data class.

Hope that helps,
D

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