Recently one of my friend asked me how to prevent class inheritance in C++. He wanted the compilation to fail.
I was thinking about it and found 3 answers. Not sure which is the best one.
1) Private Constructor(s)
class CBase
{
public:
static CBase* CreateInstance()
{
CBase* b1 = new CBase();
return b1;
}
private:
CBase() { }
CBase(CBase3) { }
CBase& operator=(CBase&) { }
};
2) Using CSealed base class, private ctor & virtual inheritance
class CSealed
{
private:
CSealed() {
}
friend class CBase;
};
class CBase : virtual CSealed
{
public:
CBase() {
}
};
3) Using a CSealed base class, protected ctor & virtual inheritance
class CSealed
{
protected:
CSealed() {
}
};
class CBase : virtual CSealed
{
public:
CBase() {
}
};
All the above methods make sure that CBase class cannot be inherited further. My Question is:
1) Which is the best method ? Any other methods available ?
2) Method 2 & 3 will not work unless the CSealed class is inherited virutally. Why is that ? Does it have anything to do with vdisp ptr ??
PS:
The above program was compiled in MS C++ compiler (Visual Studio). reference : http://www.codeguru.com/forum/archive/index.php/t-321146.html
As of C++11, you can add the final keyword to your class, eg
class CBase final
{
...
The main reason I can see for wanting to do this (and the reason I came looking for this question) is to mark a class as non subclassable so you can safely use a non-virtual destructor and avoid a vtable altogether.