When is default constructor generated in C++ [duplicate]

Answer 1

For class to be copyable, it needs to have a copy constructor. Whether you write your own, or compiler generates one for you, it doesn't matter — it has to be available for test a; test b(a); to be a valid operation.

You explicitly force compiler to delete the copy constructor — this is new version of old "make copy constructor private" trick. It disallows copying. So don't be surprised that you can't copy. Because you told the compiler to not allow it.

Answer 2

This line:

test obj2(obj1)

is trying to call the copy constructor.

Answer 3

The standard word on implicitly generated copy constructors is [class.copy]/7:

If the class definition does not explicitly declare a copy constructor, one is declared implicitly. If the class definition declares a move constructor or move assignment operator, the implicitly declared copy constructor is defined as deleted; otherwise, it is defined as defaulted (8.4). The latter case is deprecated if the class has a user-declared copy assignment operator or a user-declared destructor.

and [class.copy]/13:

A copy/move constructor that is defaulted and not defined as deleted is implicitly defined if it is odr-used (3.2) or when it is explicitly defaulted after its first declaration. [Note:The copy/move constructor is implicitly defined even if the implementation elided its odr-use (3.2, 12.2). —end note] If the implicitly-defined constructor would satisfy the requirements of a constexpr constructor (7.1.5), the implicitly-defined constructor isconstexpr.

So a copy-constructor is still generated for test, and its getting invoked by statement 2. I would believe that "Inside C++ Object Model" is talking about when a copy-constructor isn't trivial.