Example Using weak_ptr - C++ Data Type

Description

Example Using weak_ptr
Demo Code

                                                                                                                                                                                                                                                                                                                       
#include <string> 
#include <memory> 
                                                                                                                                                                                                                                                                                                                          
using namespace std;
                                                                                                                                                                                                                                                                                                                          
class Book; // forward declaration of class Book 
                                                                                                                                                                                                                                                                                                                          
class Author {//from  w w  w . ja  v a 2s .c o  m
public:
  Author(const string &authorName); // constructor 
  ~Author(); // destructor 
  void printBookTitle(); // print the title of the Book 
  string name; // name of the Author 
  weak_ptr< Book > weakBookPtr; // Book the Author wrote 
  shared_ptr< Book > sharedBookPtr; // Book the Author wrote 
};
class Book
{
public:
  Book(const string &bookTitle); // constructor 
  ~Book(); // destructor 
  void printAuthorName(); // print the name of the Author 
  string title; // title of the Book 
  weak_ptr< Author > weakAuthorPtr; // Author of the Book 
  shared_ptr< Author > sharedAuthorPtr; // Author of the Book 
};
                                                                                                                                                                                                                                                                                                                          
#include <iostream> 
                                                                                                                                                                                                                                                                                                                          
using namespace std;
                                                                                                                                                                                                                                                                                                                          
Author::Author(const string &authorName) : name(authorName)
{
}
                                                                                                                                                                                                                                                                                                                          
Author::~Author()
{
  cout << "Destroying Author: " << name << endl;
} // end of destructor 
                                                                                                                                                                                                                                                                                                                          
void Author::printBookTitle()
{
  if (shared_ptr< Book > bookPtr = weakBookPtr.lock())
  {
    cout << "Reference count for Book " << bookPtr->title << " is " << bookPtr.use_count() << "." << endl;
    cout << "Author " << name << " wrote the book " << bookPtr->title << "\n" << endl;
  }
  else // weakBookPtr points to NULL 
    cout << "This Author has no Book." << endl;
}
Book::Book(const string &bookTitle) : title(bookTitle)
{
}
                                                                                                                                                                                                                                                                                                                          
Book::~Book()
{
  cout << "Destroying Book: " << title << endl;
}
                                                                                                                                                                                                                                                                                                                          
void Book::printAuthorName() {
                                                                                                                                                                                                                                                                                                                          
}
                                                                                                                                                                                                                                                                                                                          
int main()
{
  // create a Book and an Author 
  shared_ptr< Book > bookPtr(new Book("C++"));
  shared_ptr< Author > authorPtr(new Author("book2s.com"));
                                                                                                                                                                                                                                                                                                                          
  bookPtr->weakAuthorPtr = authorPtr;
  authorPtr->weakBookPtr = bookPtr;
                                                                                                                                                                                                                                                                                                                          
  bookPtr->sharedAuthorPtr = authorPtr;
  authorPtr->sharedBookPtr = bookPtr;
                                                                                                                                                                                                                                                                                                                          
  cout << "Reference count for Book " << bookPtr->title << " is " << bookPtr.use_count() << endl;
  cout << "Reference count for Author " << authorPtr->name << " is " << authorPtr.use_count() << "\n" << endl;
                                                                                                                                                                                                                                                                                                                          
  cout << "\nAccess the Author's name and the Book's title through " << "weak_ptrs." << endl;
  bookPtr->printAuthorName();
  authorPtr->printBookTitle();
                                                                                                                                                                                                                                                                                                                          
  cout << "Reference count for Book " << bookPtr->title << " is " << bookPtr.use_count() << endl;
  cout << "Reference count for Author " << authorPtr->name << " is " << authorPtr.use_count() << "\n" << endl;
                                                                                                                                                                                                                                                                                                                          
  cout << "The shared_ptrs are going out of scope." << endl;
}
Example Using weak_ptr - C++ Data Type

Description

Demo Code

Result

Related Tutorials
