C + + Learning basics 10--transformation of a subclass object into a parent class object

one, C + + can be implemented subclass to the parent class conversion, mainly divided into three forms:

1. Object Conversion: cannot implement dynamic binding, that is, polymorphism cannot be implemented.

2. Reference conversion: dynamic binding, to achieve Polymorphism.

3. Pointer conversion: dynamic binding to achieve Polymorphism.

Note: there is generally no case where the parent class is converted to a subclass.

second, the code snippet is as Follows:

1#include <iostream>2#include <string>3 4 using namespacestd;5 6 classItem_base7 {8  public:9Item_base (Const string& is,DoubleP): ISBN ( is), price (p) {}Ten     stringbook () one     { a         returnisbn; -     } -     Virtual DoubleCalmoney (intC) the     { -         returnCprice ; -     } - Private: +     stringisbn; - protected: +     Doubleprice ;  a }; at  - classBulk_item: publicItem_base - { -  public: -Bulk_item::bulk_item (Const string& is,DoublePintCDoubledis): -Item_base ( is, p), min_py (c), discocunt (dis) {} in     DoubleCalmoney (intC) -     { to         if(c >=Min_py) +         { -             returnc * Price *discocunt; the         } *         Else $         {Panax Notoginseng             returnCprice ; -         } the     }  +     voidTest () a     { thecout<<endl<<"sub-class test!! "<<endl; +     } - Private: $     intmin_py; $     Doublediscocunt; - }; -  the //reference conversions and pointer conversions enable dynamic binding, that is, polymorphic - //object Conversions do not implement dynamic bindingWuyi  the //Object Conversions - voidTest_print_11 (ostream & out, item_base item,size_t n) wu { -      out<<"ISBN:"<<item.book () <<"\ t Total Monkey ="<<item.calmoney (n) <<endl; about }  $  - //Reference Conversions - voidTest_print_22 (ostream & out, Item_base &item,size_t N) - { a      out<<"ISBN:"<<item.book () <<"\ t Total Monkey ="<<item.calmoney (n) <<endl; + }   the  - //Pointer Conversions $ voidTest_print_33 (ostream & out, Item_base *item,size_t N) the { the      out<<"ISBN:"<<item->book () <<"\ t Total Monkey ="<<item->calmoney (n) <<endl; the }  the  - intMain () in { theItem_base Item ("X-123-1234-x",10.0); the      aboutBulk_item item2 ("123-456-x",10.0,Ten,0.8); the      theTest_print_11 (cout,item,Ten);//object Conversions do not implement polymorphism theTest_print_11 (cout,item2,Ten); +      -cout<<endl; theTest_print_22 (cout,item,Ten);//Reference ConversionsBayiTest_print_22 (cout,item2,Ten); the      thecout<<endl; -Test_print_33 (cout,&item,Ten);//Pointer Conversions -Test_print_33 (cout,&item2,Ten); the     return 0; the}

C + + Learning basics 10--transformation of a subclass object into a parent class object