What does a compiler add to an empty class declaration?

Question

Suppose, I write

class A { };

The compiler should provide (as and when needed)

1. a constructor
2. a destructor
3. a copy constructor
4. = operator

Is this all the compiler provides? Are there any additions or deletions to this list?

Hive

I came across this old question just now... for the benefit of future visitors it's probably worth mentioning that in C++11 a move constructor as well as a move assignment operator are auto-generated in addition to the above. – Chlorine

Answer 1

It's complete. But there are two points you should note:

1. It's the copy =operator. Just like there is a copy constructor, there is a copy assignment operator.
2. They are only provided if actually used.

Some explanation for 2:

struct A { private: A(); };
struct B : A { };

That's fine! Providing a default constructor would be ill-formed for "B", because it would not be able to call the base-class' constructor. But the default constructor (and the other special functions) is only provided (we say it's implicitly defined) if it's actually needed.

Electromagnetic

I guess you could argue that in the case of an empty class, the compiler also adds at least one byte of padding ;-) – Leucomaine

Answer 2

From C++11 onwards, in addition to what you have listed

• Move ctor
• Move assignment operator

Haleigh

Answer 3

Your list is complete. This is all it is adding.

Joke

Answer 4

The list is not completed............ In addition with the above mention FOUR properties , there is an address operator ( & ) overloaded method , that return the address of the invoking object , is also provided automatically by the compiler.

Arce

Answer 5

There are five properties:

constructor

copy constructor

destructor

assignment operator

the reference operator(&) - the address

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