Declaration and use of C + + base class, derived class object pointers

1. class pointers, object pointers

Class x{

...

Public

Voidshow ();

};

Main ()

{

x X1,*PTR1; A pointer to the object X1 and class X defining Class X Ptr1

x X2,*PTR2; A pointer to the object X2 and Class X defining Class X PTR2

X*PTR3; Defines a pointer to class X PTR3

...

PTR1 =&x1; Point pointer ptr1 to X1 object

PTR2 =&x2; Point pointer ptr2 to X2 object

Ptr1-> Show (); //

Ptr2-> Show (); //

Ptr3-> Show (); Pointer PTR3 directly to the class, calling the class public segment member function

}

2. Introduction of object pointers after derived classes

(1) A pointer to a base class object points to its public-derived object, pointing to a private derived object error;

eg

Class base{

...

};

Class derive:base{

...

};

Main ()

{

Base Obj1, *PTR1;

derive = Obj2;

PTR1 = &obj1;

PTR1 = &obj2; Error, pointing to a private derived class object

}

(2) A pointer to a derived class object cannot point to the object of the base class;

eg

Main ()

{

Base Obj1, *PTR1;

Derive Obj2, *PTR2;

PTR2 = *obj2; Point the pointer ptr to a derived class object Obj2

PTR2 = *obj1; Error

...

}

(3) A pointer to a base class object that, when pointed to a derived class object, can only point directly to a member in the derived class that inherits from the base class and does not have direct access to a particular member of the derived class;

(4) But other methods can be used to implement pointers to specific members in derived classes

eg

Class base{

...

Public

Voidshow ();

Voidshow1 ();

};

Class Derive:public base{

...

Public

Voidshow ();

Voidshow2 ();

};

Main ()

{

Base Obj1, *PTR1;

Derive Obj2, *PTR2;

PTR1 = &obj1; The pointer points to the base class object Obj1

PTR1, show (); Call the public segment member function of base class base show

PTR1 = &obj2; The pointer points to the derived class object Obj2

PTR1, show (); Calling a derived class object obj2 a public segment member function inherited from a base class show

((derive *) ptr1), show (); Calling a specific member function of a derived class object Obj2 show ()

((derive *) ptr1), Show2 (); Calling a derived class object obj2 a specific member function Show2 ()

PTR1 = &obj1; The pointer re-points to the base class object Obj1

PTR1, Show1 (); Call the base class public segment member function Show1 ()

}

Declaration and use of C + + base class, derived class object pointers