Default move constructor in a sub class

Question

In C++11, if the base class has defined its own move (copy) constructor (assignment operator), does its subclass need to define its own move (copy) constructor (assignment operator) in where call the base class's corresponding constructor/operator is called explicitly?

Is it a good idea to define the constructor, destructor, move/copy constructor (assignment operator) clearly every time?

struct Base {
    Base() {}
    Base(Base&& o);
};

struct Sub : public Base {
    Sub(Sub&& o) ;  // Need I do it explicitly ? If not,what the compiler will do for me
};

Answer 1

The compiler will generate a default move constructor if you don't specify one in the base class (except some cases, e.g. there's a base class with a deleted move constructor) but you should, in any case, call explicitly the base class' one if you have it:

Sub(Sub&& o) : Base(std::move(o))

Answer 2

According to the standard (N3797) 12.8/9 Copying and moving class objects [class.copy]:

If the definition of a class X does not explicitly declare a move constructor, one will be implicitly declared as defaulted if and only if

— X does not have a user-declared copy constructor,

— X does not have a user-declared copy assignment operator,

— X does not have a user-declared move assignment operator, and

— X does not have a user-declared destructor.

As such, if your class meets the above requirements then a default move constructor will be implicitly declared for you.

As already being stated, the base-class has no knowledge of any sub-classes. As such, whether you declare a move constructor in one base class has no effect on the implicit generation of a move constructor in its sub-classes.

As far as it concerns whether you should declare explicitly a constructor/destructor etc. of a class, there's this nice article.