Are move constructors produced automatically?

Question

I have a big class holding a lot of STL containers.
Will the compiler automatically make a move constructor that will move those containers to the target or I have to make my own?

Answer 1

A move constructor for a class X is implicitly declared as defaulted exactly when

• 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,
• X does not have a user-declared destructor, and
• the move constructor would not be implicitly defined as deleted.

So for example, if your class has a class type data member that does not have a move constructor, your class will not get a move constructor even if it doesn't have any copy/move constructor declared, because the implicitly declared move constructor would be defined as deleted (because of that data member).

Answer 2

Default move constructors are generally tied to default copy constructors. You get one when you get the other. However, if you write a copy constructor/assignment operator, then no default copy and move constructors/assignment operators are written. If you write one of either set, you must write them all.