How to use inheritance and virtual functions in a container in C + +

The container does not support mixed types, and derived-base conversions (Derived-base conversion) cannot be used if the derived class object is stored directly into the base class container;

Because the conversion can occur only in pointers and references, it cannot occur directly to the object, and if it is directly converted, truncation will occur (sliced down);

That is, the derived class is partially excised, leaving only the base class part; Therefore, the derived class stored in the container is exported as a virtual function of the base class part;

If you want to inherit in a container, you need to use a pointer, including a smart pointer, such as:shared_ptr<>, to output a virtual function of the overridden (override) version of the derived class;

Code:

* * * CppPrimer.cpp * * Created on:2013.11.12 * author:caroline//*eclipse cdt*/#includ E <iostream> #include <string> #include <vector> #include <memory> #include <cstddef&gt  
      
;  
      
using namespace Std;  
    Class Quote {public:quote () = default; Quote (const std::string& book, double sales_price): Bookno (book), Price (Sales_price) {} Std::strin  
    G ISBN () const {return bookno;} Virtual Double Net_price (std::size_t N) const {return n price;}//virtual function virtual ~quote () = default;  
Dynamic binding destructor private:std::string Bookno;  
Protected://protected type Double price = 0.0;  
      
};  
    Class Disc_quote:public Quote {//abstract base class public:disc_quote () = default; Disc_quote (const std::string&, double, std::size_t qty, double Disc): Quote (book, price), quant ity (qty), Discount (disc) {} double Net_price (std::size_t) const= 0;  
        Pure virtual function protected:std::size_t quantity = 0;  
Double discount = 0.0;  
      
};  
    Class Bulk_quote Final:public disc_quote {//final qualifier, cannot be inherited public:bulk_quote () = default;  Bulk_quote (const std::string& book, double p, std::size_t qty, double disc): Disc_quote (Book, p, qty, disc)  
{}///Using the constructor of the base class double Net_price (std::size_t cnt) const override;  
      
}; Double Bulk_quote::net_price (std::size_t cnt) const {if (CNT >= quantity) return CNT * (1-discount) *  
    Price  
else return CNT * price; Double Print_total (std::ostream &os, const quote& Item, std::size_t N) {double ret = item.net_  
    Price (n); Os << "ISBN:" << item.isbn () << "# Sold:" << n << "total due:" << ret << St  
    D::endl;  
return ret;  
    the int main (void) {//Normal store cannot invoke the virtual function of the derived class std::vector<quote> basket; Basket.pusH_back (Quote ("Cppprimer", 50));  
    Basket.push_back (Bulk_quote ("Cppprimer", 50, 10,. 25));  
      
    Std::cout << "bulk_quote:" << basket.back () net_price << Std::endl;  
    Use the pointer to store, can correctly call std::vector<std::shared_ptr<quote> > sbasket;  
    Sbasket.push_back (std::make_shared<quote> ("Cppprimer", 50));  
    Sbasket.push_back (std::make_shared<bulk_quote> ("Cppprimer", 50, 10,. 25));  
      
      
    Std::cout << "bulk_quote:" << sbasket.back ()->net_price << Std::endl;  
      
return 0; }

Output:

bulk_quote:1000  
bulk_quote:750

Author: csdn Blog spike_king

More Wonderful content: http://www.bianceng.cnhttp://www.bianceng.cn/Programming/cplus/