A detailed explanation of the structure and destructor order of derived classes in C + +

Derived classes are constructed and refactored in a certain order because they want to invoke the base class;

The order of the constructs is: base (base)-> derivation (derived), that is, the base class is constructed first, and then the derived class is constructed;

Because the base class is independent of the derived class, the object in the derived class is not invoked, so it should be generated first;

If a derived class is built before the base class, it is possible that the build fails because the base class resource cannot be invoked;

The order of the destructor is: derivation (derived)-> base (base); The derived class is released first, then the base class is released;

Because the derived class needs to release the invoked base class resource first, it should be released preferentially;

If the base class is first destructor, it is possible that some of the resources are occupied by the derived class, which may cause the destructor to fail;

The structure and the destructor order of the derived class are just the opposite;

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 () {std::cout << "This is Quote constructor" << Std::endl; } Quote (const std::string& book, double sales_price): Bookno (book), Price (Sales_price) {} St  
    D::string ISBN () const {return bookno} Virtual Double Net_price (std::size_t N) const {return n-price;}//virtual function//virtual ~quote () = default;  
    Dynamic binding destructor Virtual ~quote () {std::cout << "This is Quote destructor" << Std::endl;  
} private:std::string Bookno;  
Protected://protected type Double price = 0.0;  
}; * More Highlights: http://www.bianceng.cnhttp://www.bianceng.cn/programming/cplus/*/
Class Disc_quote:public Quote {//abstract base class public://disc_quote () = default;  
    Disc_quote () {std::cout << "This is Disc_quote constructor" << Std::endl; } disc_quote (const std::string& book, double Price, std::size_t qty, double Disc): Quote (book, Price ), Quantity (qty), Discount (disc) {} double Net_price (std::size_t) const = 0; Pure virtual function Virtual ~disc_quote () override{std::cout << "This is Disc_quote destructor" << std::en  
    dl  
        } 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 () {std::cout << "This is Bulk_quote constructor" << Std::endl; } bulk_quote (const std::string& book, double p, std::size_t qty, double disc): Disc_quote (Book, p, QT Y, disc) {}//using the constructor of the base class DoubLe Net_price (std::size_t cnt) const override;  
    Virtual ~bulk_quote () override{std::cout << "This is Bulk_quote destructor" << Std::endl;  
      
}  
}; 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) {bulk_quote* BQ = new Bulk_quote;  
      
    Delete Bq;  
      
return 0; }

Output:

This is Quote constructor this are  
Disc_quote constructor This is  
Bulk_quote constructor This is  
bulk_quote des Tructor this are  
disc_quote destructor This is  
quote destructor

Author: csdn Blog spike_king