What is the cost of inheritance?

Question

This is a pretty basic question but I\'m still unsure:

If I have a class that will be instantiated millions of times -- is it advisable not to derive it from some o

Answer 1

Creating a derived object involves calling constructors for all base classes, and destroying them invokes destructors for these classes. The cost depends then on what these constructors do, but then if you don't derive but include the same functionality in derived class, you pay the same cost. In terms of memory, every object of the derived class contains an object of its base class, but again, it's exactly the same memory usage as if you just included all of these fields in the class instead of deriving it.

Be wary, that in many cases it's a better idea to compose (have a data member of the 'base' class rather than deriving from it), in particular if you're not overriding virtual functions and your relationship between 'derived' and 'base' is not an "is a kind of" relationship. But in terms of CPU and memory usage both these techniques are equivalent.