The relationship of pointers such as C + +

1 base class pointers and derived class pointers may match 4 of base class objects and derived class objects:

Reference a base class object directly with a base class pointer, referencing a derived class object directly with a derived class pointer, referencing a derived class object with a base class pointer, and referencing a base class object with a derived class pointer. 2. Base-class pointers refer to derived class objects

For example:

A * p; Pointer to an object of type A

A A_obj; Object of type A

B B_obj; Object of type B

p = & a_obj; P points to the object of type A

p = & b_obj; P refers to the object of type B, which is a derived class

With P, all elements inherited from class A can be accessed through b_obj,

However, you cannot use p to access a class B custom element (unless an explicit type conversion is used)

1#include <iostream>2#include <cstring>3 using namespacestd;4 5 6 //referencing a derived class object using a base-class pointer7 classA8 {9     Charname[ -];Ten  Public: One     voidSetName (Char*s) A     { - strcpy_s (name,s); -     } the     voidprint () -     { -cout <<"name ="<< name <<Endl; -     } + }; -  + classB: PublicA A { at         Charphone_num[ -]; -  Public: -     voidSetnum (Char*num) -     { - strcpy_s (phone_num,num); -     } in     voidPrintnum () -     { tocout <<"Phone_num ="<< Phone_num <<Endl; +     } - }; the  * voidMain () $ {Panax Notoginseng     //base class pointers -A *ap; the     //base class Object + A; A     //derived class object the b b; +     //base-class pointers point to base class objects -AP = &A; $     //to call a member function of a base class using a base class pointer $Ap->setname ("Tangxiaoxue"); -Ap->print (); -     //base-class pointers point to derived class objects theAP = &b; -     //to invoke a member function inherited from a base class using a base class pointerWuyiAp->setname ("Dujingui"); theAp->print (); -     //to invoke a member function of a derived class using a derived class object WuB.setnum ("15110711517"); -     //strongly-typed conversions to base-class pointers, calling member functions of derived classes About((b*) AP)printnum (); $}

3. Derived class pointers refer to base class objects

1#include <iostream>2 using namespacestd;3 4 classData5 {6  Public:7Data (intYintMintd)8     {9 SetData (y,m,d);Ten     } One     voidSetData (intYintMintd) A     { -Year =y; -mouth =m; theDay =D; -     } -     voidprint () -     { +cout << Year <<"-"<< Mouth <<"-"<< Day <<";"; -     } + protected: A     intYear,mouth,day; at }; -  - classDatatime: PublicData - { -  Public: -Datatime (intYintMintDintHintMiints):D ata (y,mi,d) in     { - settime (h,mi,s); to     } +     voidSetTime (intHintMints) -     { theHours =h; *minutes =m; $Second =s;Panax Notoginseng     } -     voidprint () the     { +         //make a type conversion to the this pointer, call the base class member function A         //( (data*) This)->print (); equivalent to Data::p rint () the Data::p rint (); +cout << hours <<":"<< minutes <<":"<< Second <<Endl; -     } $ Private: $     intHours,minutes,second; - }; -  the voidMain () - {WuyiDatatime D (1995, A, -, A, -, -); the d.print (); -}

The relationship of pointers such as C + +