C++ Add this pointer to a container by calling it in base class constructor

Question

class Base
{
public:
Base (int a, int b);
private:
int a,b;
};

class Derived1
{
public:
Derived1():base(1,2){}
};

similarly Derived2, Derived 3 which doesnt contain any data members on its own

Now i need to contain these derived objects in a singleton, so i was thinking to call this in base constructor like

Base::Base(int a, int b)
{
CBaseMgr::GetInstance()->AddtoVector(this);
}

so now if i construct

Derived d1, d2, d3 etc. will the Singleton's container contain all derived objects?

My doubt is can i do this adding of objects to container in base ctor or should i do in derived ctor.?

Answer 1

If all the derived class call this base class constructor, yes, you should be fine.

Just beware of the copy constructor which, if not overloaded, will not add this to your global vector.

I suppose you want as well remove the instances that were destroyed, from the global vector ?

If so, don't forget to declare Base::~Base to be virtual, so that he gets called by derived classes.

Answer 2

Doing this in Base's constructor should be fine, as long as you're not dereferencing this before the whole construction is done.

Answer 3

My doubt is can i do this adding of objects to container in base ctor or should i do in derived ctor.?

You can safely do it in the base constructor but you have to take care of the following:

• explicitely declare copy constructor semantics (if you want objects to be copy-constructible, fine; if not, declare the base copy constructor as private, and do not implement it, or make Base inherit privately from boost::noncopiable).

• store Base references as pointers (I guess you already know this).

• declare base's destructors virtual (and have them remove the instance from the manager)

• make sure the removal process doesn't throw any exceptions ( throwing exceptions in destruction may lead to transforming the Earth into a singularity or other undefined behaviour :) ).