94 lines
3.6 KiB
C++
94 lines
3.6 KiB
C++
// fig20_08.cpp
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// Demonstrate shared_ptrs.
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#include <algorithm>
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#include <fmt/format.h>
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#include <iostream>
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#include <memory>
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#include <string>
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#include <string_view>
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#include <vector>
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// class Book
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class Book {
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public:
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explicit Book(std::string_view bookTitle) : title{bookTitle} {}
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~Book() { std::cout << fmt::format("Destroying Book: {}\n", title); }
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std::string title; // title of the Book
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};
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// a custom delete function for a pointer to a Book
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void deleteBook(Book* book) {
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std::cout << "Custom deleter for a Book, ";
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delete book; // delete the Book pointer
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}
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// compare the titles of two Books for sorting
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bool compareTitles(
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std::shared_ptr<Book> ptr1, std::shared_ptr<Book> ptr2) {
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return (ptr1->title < ptr2->title);
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}
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int main() {
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// create a shared_ptr to a Book and display the reference count
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std::shared_ptr<Book> bookPtr{
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std::make_shared<Book>("C++ How to Program")};
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std::cout << fmt::format("Reference count for Book {} is: {}\n",
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bookPtr->title, bookPtr.use_count());
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// create another shared_ptr to the Book and display reference count
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std::shared_ptr<Book> bookPtr2{bookPtr};
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std::cout << fmt::format("Reference count for Book {} is: {}\n",
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bookPtr->title, bookPtr.use_count());
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// change the Book’s title and access it from both pointers
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bookPtr2->title = "Java How to Program";
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std::cout << fmt::format(
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"Updated Book title:\nbookPtr: {}\nbookPtr2: {}\n",
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bookPtr->title, bookPtr2->title);
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// create a std::vector of shared_ptrs to Books (BookPtrs)
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std::vector<std::shared_ptr<Book>> books{
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std::make_shared<Book>("C How to Program"),
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std::make_shared<Book>("Intro to Python"),
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std::make_shared<Book>("C# How to Program"),
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std::make_shared<Book>("C++ How to Program")};
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// print the Books in the vector
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std::cout << "\nBooks before sorting:\n";
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for (auto book : books) {
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std::cout << book->title << "\n";
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}
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// sort the vector by Book title and print the sorted vector
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std::sort(books.begin(), books.end(), compareTitles);
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std::cout << "\nBooks after sorting:\n";
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for (auto book : books) {
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std::cout << book->title << "\n";
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}
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// create a shared_ptr with a custom deleter
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std::cout << "\nshared_ptr with a custom deleter.\n";
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std::shared_ptr<Book> bookPtr3{
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new Book("Android How to Program"), deleteBook};
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bookPtr3.reset(); // release the Book this shared_ptr manages
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// shared_ptrs are going out of scope
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std::cout << "\nEnd of main: shared_ptr objects going out of scope.\n";
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}
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/**************************************************************************
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* (C) Copyright 1992-2022 by Deitel & Associates, Inc. and *
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* Pearson Education, Inc. All Rights Reserved. *
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* *
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* DISCLAIMER: The authors and publisher of this book have used their *
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* best efforts in preparing the book. These efforts include the *
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* development, research, and testing of the theories and programs *
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* to determine their effectiveness. The authors and publisher make *
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* no warranty of any kind, expressed or implied, with regard to these *
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* programs or to the documentation contained in these books. The authors *
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* and publisher shall not be liable in any event for incidental or *
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* consequential damages in connection with, or arising out of, the *
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* furnishing, performance, or use of these programs. *
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**************************************************************************/
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