In which cases there is no constructor at all, even a default constructor?

Question

In this book I am currently reading I ran across this:

A class doesn't need a constructor. A default constructor is not needed if the object doesn't need initialization.

Am I correct in inferring from the above that the compiler does not generate a default constructor for the class/structure in some cases? If yes, what are those cases? I will venture and say POD is probably one. Are there any other?

EDIT: I have changed the title as the original title gave the meaning that I asked when was a default constructor not defined instead of asking when does a class not have a constructor at all.

Answer 1

A class doesn't need a constructor. A default constructor is not needed if the object doesn't need initialization.

I think the author is talking about this situation:

some_type some_function () {
   POD_type this_is_intentionally_uninitialized;
   ...
}

Under some circumstances a constructor won't be called, period. As soon as you write a constructor you don't have a POD class, so now the constructor will be called.

Whether it is a good or bad thing to have an object running around that contains random, uninitialized data is a different question entirely.