How to Deep Copy Values of Vector Pointer (Not just the pointer)?

Question

I've an operator and function which goal is to copy the values of the vector pointer to a vector. I've read that as long it's a vector pointer, deep copying methods would only copy its pointer, not its value. I'm wondering how to copy it's values over instead. (The vector is a member of CObject class)

Operator function:

void CObject::operator=(CObject& rhs)
{
    this->ClearObject();   //Object will be cleared first
    // How to perform the deep copy below?
    copy(rhs.m_Vector.begin(), rhs.m_Vector.end(), back_inserter(this->m_Vector));
}

Declared as -> void operator=(CObject& rhs);

Example application of operator function (Performed in another class) :

CObject* m_pObjectOne;
CObject  m_ObjectTwo;

m_ObjectTwo = m_pObjectOne;

(Therefore, when m_pObjectOne is deleted in its class destructor, m_ObjectTwo loses its value)

Vector & others:

struct OBJECT_ITEM
{
    char  m_chType;
    UINT  m_nDataByte;
    BYTE* m_pData;
    CString m_strRecipeTag;
}

std::vector<OBJECT_ITEM> m_Vector;

I've also tried other deep copy methods like push_back() & assign() but it gives me the same result.

Any help would be appreciated!

Answer 1

Strive for the "rule of zero".

How to Deep Copy Values of Vector Pointer (Not just the pointer)?

Basically - don't. You should strive to follow the rule of zero : Unless otherwise necessary, set things up so that the default constructors, assignment operators and destructors do what they should.

In your case: Suppose you let CObject use its default (copy) assignment operator. That means, that rhs.m_Vector will be assigned to lhs.m_Vector . And vector assignment means that individual members of the vector are assigned to their corresponding members.

The way you wrote your vector, that won't do what you want: You wrote you want to avoid the case of "when m_pObjectOne is deleted in its class destructor, m_ObjectTwo loses its value)". Well, since you're willing to hold copies of the objects, consider something like the following:

struct OBJECT_ITEM
{
    char  m_chType;
    UINT  m_nDataByte;
    MyContainer m_upData;
    CString m_strRecipeTag;
}

And choose or write MyContainer to suit your needs. It could just be an std::vector<BYTE> ; or if you don't want the size to change after construction, use a dynarray (not in the standard library these days; here's an alternative ); etc. And your chosen container will actually get properly copied when you copy an OBJECT_ITEM . Finally, don't hold pointers to OBJECT_ITEM 's - just hold actual OBJECT_ITEM 's (which it seems you were already doing?)

And there, now you can no longer have dangling pointers - with no custom constructors, assignment operators or anything else like that.