C ++ basic tutorial (original)

1: each time a class is loaded, only the constructors at the time of loading are used. That is to say, when multiple constructors are defined in the class, only one of them can be used.
2: When no constructor is specified for the base class, all constructor defined by the inherited class cannot specify the base class constructor called, or
By default, only the default constructor of the base class is called.
3: When the base class only defines the default constructor, all constructor that inherits the class definition can only be specified to call the default constructor of the base class, or
By default, the default constructor of the base class is called.
4: when the base class defines multiple constructors, all constructors that inherit the class definition can specify to call the Default constructors of the base class at will.
If this parameter is not specified, the default constructor of the base class is called.

Subclass
1: When the inherited class object is copied to the base class object, the base class object can reference all available resources of the base class, but cannot reference the members of the inherited class.
In this case, the member value of the base class object is updated without affecting the state of the inherited class subobject. On the contrary, it cannot be copied, which is called subclass.
2: If the assigned object is of the pointer type, the pointer of the inherited object is assigned to the pointer variable of the base class. At this time, the member value of the base class object is updated.
, Affects the State of the Child object of the inheritance class, because the pointer variable points to the inherited class object.