Question

Problem: I need an array (datamember) in a parent class A.
However, depending on the child class, that array should have a different number of elements.

Is this possible?
If yes, how can I do this? (without dynamic allocation)
If no, then is there any way around? (without dynamic allocation)

Thanks

Answer 1

It depends on how you plan on using said parent class, but you can accomplish what you’ve described using templates.

template<size_t N>
class Parent
{
    int data[N];
}

class Child : public Parent<4>
{
}

This has many limitations (such as being unable to use a Parent class pointer really), but it avoids having the dynamic allocation.

EDIT — Since you need true access to a parent array, here is an alternative.

class Parent
{
    const size_t mSize;

public:
    Parent(size_t size) : mSize(size) {}

    inline size_t Size() { return mSize; }
    virtual int* GetData() = 0;
}

template<size_t N>
class Child : public Parent
{
    int mData[N];

public:
    Child() : Parent(N) {}

    virtual int* GetData() { return mData; }
}

class Grandchild : public Child<8>
{
public:
    GrandChild() {}
}