Pure virtual Functions in C + + (pure virtual) and abstract base class (abstract base Class)

A pure virtual function (pure virtual) is a method in a base class, just a declaration, not a definition, is a generalization concept (general concept);

is to put the corresponding virtual function, the end of the Add "= 0", the virtual function becomes a pure virtual function, you can not add a definition;

If it is another virtual function, it must be defined (define), even if it is not used;

A base class that contains pure virtual functions, an abstract base class (abstract base class) that cannot be defined (object) and can only be used as an inheritance define;

Code:

* * * CppPrimer.cpp * * Created on:2013.11.12 * author:caroline//*eclipse cdt*//* More highlights: http: www.bianceng.cnhttp://www.bianceng.cn/programming/cplus/*/#include <iostream> #include <string> #  
      
Include <cstddef> 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;  
    int main (void) {Quote Q ("Cppprimer", 99); Bulk_quote BQ ("Cppprimer", 99, 10, 0.5);  
    quote& RQ = BQ;  
    std::size_t n = 20;  
    Std::cout << "We want to buy" << N << "books." << Std::endl;  
    Std::cout << "Quote net_price:" << q.net_price (n) << Std::endl;  
    Std::cout << "Bulk_quote net_price:" << bq.net_price (n) << Std::endl;  
      
    Std::cout << "R Quote net_price:" << rq.net_price (n) << Std::endl;  
    Dynamic binding Quote Base ("Effectivecpp", 50);  
    Print_total (cout, base, 10);  
    Bulk_quote derived ("Effectivecpp", 50, 5,. 19);  
      
    Print_total (cout, derived, 10);  
    Copy-assignment operation, derived class-> base = derived;  
      
    Std::cout << "Net_price:" << base.net_price << Std::endl; Double undiscounted = derived. Quote::net_price (20);  
    Derived classes use the virtual functions of the base class Std::cout << "undiscounted:" << undiscounted << Std::endl;  
      
return 0; }

Author: csdn Blog spike_king