pointer vs non-pointer members of a class

Question

My questions is, suppose we have two classes A and B. I want to have an object of B in class A.

Should I use,

class A
{
  public:
          A();
          ~A();
          B* b;
};

or

class A
{
      public:
              A();
              ~A();
              B b;
};

As far as I know, in the first scenario, I can initialize the object *b using new operator and for the second scenario, I can initialize b using an initialization list if I don't want to use the default constructor of class B. Which is more convenient to use?

Answer 1

It depends.

Even if you use the pointer, you can initialize the member in the initialization list, but that's not your biggest concern.

There are advantages and disadvantages to both:

Using a pointer:

Pros:

• the class will be smaller in memory

• you only need a forward declaration to the other class - no need to include the other header in your header

• can use derived objects from B as members

Cons:

• memory management - this is a pretty big one. Do you want the memory to be managed by the class (override destructor, assignment operator and copy constructor)?

Using an object:

Pros:

• no need to worry about memory management

Cons:

• can only use objects of the base class. What if you want to derive from B?

• more memory for each instance

• constructor of B will be called on construction of A

• you need the full definition of B inside the header

I'll edit my answer if I think of more.