Reference Counted shared_ptr - C++ Data Type

C++ examples for Data Type:shared_ptr

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Description

Reference Counted shared_ptr

Demo Code

                                                                                                                                                                                                                                                                                                                      
#include <string> 
using namespace std; 
                                                                                                                                                                                                                                                                                                                      
class Book //from  w w w.j a  va2s. c  o  m
{ 
public: 
    Book( const string &bookTitle ); // constructor 
    ~Book(); // destructor 
    string title; // title of the Book 
}; 
                                                                                                                                                                                                                                                                                                                      
// Member-function definitions for class Book. 
#include <iostream> 
#include <string> 
using namespace std; 
                                                                                                                                                                                                                                                                                                                      
Book::Book( const string &bookTitle ) : title( bookTitle ) 
{ 
} 
                                                                                                                                                                                                                                                                                                                      
Book::~Book() 
{ 
    cout << "Destroying Book: " << title << endl; 
} // end of destructor 
                                                                                                                                                                                                                                                                                                                      
#include <algorithm> 
#include <iostream> 
#include <memory> 
#include <vector> 
using namespace std; 
                                                                                                                                                                                                                                                                                                                      
typedef shared_ptr< Book > BookPtr; // shared_ptr to a Book 
                                                                                                                                                                                                                                                                                                                      
void deleteBook( Book* book ) 
{ 
   cout << "Custom deleter for a Book, "; 
   delete book; // delete the Book pointer 
}
bool compareTitles( BookPtr bookPtr1, BookPtr bookPtr2 ) 
{ 
   return ( bookPtr1->title < bookPtr2->title ); 
}
                                                                                                                                                                                                                                                                                                                      
int main() 
{ 
   BookPtr bookPtr( new Book( "C++" ) ); 
   cout << "Reference count for Book " << bookPtr->title << " is: " << bookPtr.use_count() << endl; 
                                                                                                                                                                                                                                                                                                                      
   // create another shared_ptr to the Book and display reference count 
   BookPtr bookPtr2( bookPtr ); 
   cout << "Reference count for Book " << bookPtr->title << " is: " << bookPtr.use_count() << endl; 
                                                                                                                                                                                                                                                                                                                      
   bookPtr2->title = "Java"; 
   cout << "The Book's title changed for both pointers: " 
       << "\nbookPtr: " << bookPtr->title 
       << "\nbookPtr2: " << bookPtr2->title << endl; 
                                                                                                                                                                                                                                                                                                                      
   // create a std::vector of shared_ptrs to Books (BookPtrs) 
   vector< BookPtr > books; 
   books.push_back( BookPtr( new Book( "C" ) ) ); 
   books.push_back( BookPtr( new Book( "VB" ) ) ); 
   books.push_back( BookPtr( new Book( "C#" ) ) ); 
   books.push_back( BookPtr( new Book( "C++" ) ) ); 
                                                                                                                                                                                                                                                                                                                      
   // print the Books in the vector 
   cout << "\nBooks before sorting: " << endl; 
   for ( int i = 0; i < books.size(); ++i ) 
       cout << ( books[ i ] )->title << "\n"; 
                                                                                                                                                                                                                                                                                                                      
   // sort the vector by Book title and print the sorted vector 
   sort( books.begin(), books.end(), compareTitles ); 
   cout << "\nBooks after sorting: " << endl; 
   for ( int i = 0; i < books.size(); ++i ) 
       cout << ( books[ i ] )->title << "\n"; 
                                                                                                                                                                                                                                                                                                                      
   // create a shared_ptr with a custom deleter 
   cout << "\nshared_ptr with a custom deleter." << endl; 
   BookPtr bookPtr3( new Book( "Small C++ How to Program" ), deleteBook); 
   bookPtr3.reset(); // release the Book this shared_ptr manages 
                                                                                                                                                                                                                                                                                                                      
   // shared_ptrs are going out of scope 
   cout << "\nAll shared_ptr objects are going out of scope." << endl; 
}

Result


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