Inheritance and Polymorphism of C++ Classes

C++ object oriented

• The two main characteristics of object orientation are: inheritance and polymorphism

roaming

• By default, the resolution of member functions is done dynamically at compile time. If it needs to be done dynamically at runtime, we need to add the virtual keyword before its declaration.
• If there is a class A, which is the base class of class B, when an object of class B is defined, the constructors and destructors of both A and B will be executed (execution order is reversed).
• If there are multiple levels of derivation, the constructor and destructor of the base class will be called in turn until there is no base class.

• A static member function cannot be declared virtual

• LibMat.h

  #ifndef  LIBMAT_H
  #define LIBMAT_H
  
  #include <cstdlib>
  #include <string>
  #include <iostream>
  #include <ostream>
  #include <assert.h>
  #include <time.h>
  #include <algorithm>
  #include <functional>
  #include <iterator>
  #include <fstream>
  #include <vector>
  using namespace std;
  
  class LibMat
  {
  public:
      LibMat()
      {
          cout << "LibMat::LibMat() default constructor!" << endl;
      }
  
      // 对于经过virtual修饰的member function，会在runtime进行动态解析
      virtual ~LibMat()
      {
          cout << "LibMat::~LibMat() default destructor!" << endl;
      }
      virtual void print() const
      {
          cout << "LibMat::print() -- I am a LibMat object!" << endl;
      }
  
  };
  #endif
  

• Book.h

  #ifndef  BOOK_H
  #define  BOOK_H
  
  #include "LibMat.h"
  using namespace std;
  
  class Book : public LibMat
  {
  public:
      Book(const string &title, const string& author)
          :_title(title), _author(author)
      {
          cout << "Book::Book( " << _title << ", "
              << _author << " ) constructor" << endl;
      }
  
      virtual ~Book()
      {
          cout << "Book::~Book() default destructor!" << endl;
      }
  
      virtual void print()
      {
          cout << "Book:print() -- I am a Book object." << endl
              << "\tMy title is: " << _title << endl
              << "\tMy author is: " << _author << endl;
      }
  
      const string &title() const { return _title; }
      const string &author() const { return _author; }
  
  protected:
      string _title;
      string _author;
  };
  #endif
  

• AudioBook.h

  #ifndef  AUDIOBOOK_H
  #define  AUDIOBOOK_H
  
  #include "Book.h"
  using namespace std;
  
  class AudioBook : public Book
  {
  public:
      AudioBook(const string &title, const string& author, const string& narrator)
          :Book(title, author), _narrator(narrator)
      {
          cout << "AudioBook::AudioBook( " << _title << ", "
              << _author << ", " << _narrator  << " ) constructor" << endl;
      }
  
      virtual ~AudioBook()
      {
          cout << "AudioBook::~AudioBook() default destructor!" << endl;
      }
  
      virtual void print()
      {
          cout << "AudioBook:print() -- I am a AudioBook object." << endl
              << "\t\tMy title is: " << _title << endl
              << "\t\tMy author is: " << _author << endl
              << "\t\tMy narrator is: " << _narrator << endl;
      }
  
      const string &narrator() const { return _narrator; }
  
  
  protected:
      string _narrator;
  };
  #endif
  

• main.cpp

  #include "AudioBook.h"
  using namespace std;
  typedef long long ll;
  
  // 当定义一个派生对象时，基类和派生类的constructor都会被执行，destructor也都会被执行（但是次序颠倒）
  void testClass()
  {
      //LibMat mat;
      //mat.print();
  
      //Book book("book1", "author1");
      //book.print();
  
      AudioBook abook("book2", "author2", "narrator2");
      abook.print();
  
  }
  
  int main()
  {
      // 按照时间来初始化种子，保证每次结果不一样
      srand( (int)time(0) );
      //cout << rand() << endl;
  
      testClass();
  
      system("pause");
      return 0;
  }
  

other

• For the class member function of static type, you need to declare it outside the class (usually in the h file), and then define it (can be in the cpp file or the h file), otherwise there will be unresolved externalserrors like this, you can Refer to this thread: https://bbs.csdn.net/topics/320269587