Lots of ChatGPT Output
"write me an exercise through which I can learn about smart pointers"
Certainly! Below is an exercise that will help you learn about C++ smart pointers, specifically std::unique_ptr, std::shared_ptr, and std::weak_ptr. By following this exercise, you’ll get hands-on practice with smart pointers and their key features.
Exercise: Smart Pointers in C++
Goal:
Implement a simple memory management system where you manage a set of Book objects using smart pointers. You’ll practice creating and manipulating unique_ptr, shared_ptr, and weak_ptr.
Step 1: Define the Book class
Start by defining a Book class with a constructor, a destructor, and a method to display the book’s information.
#include <iostream>
#include <memory>
#include <vector>
#include <string>
class Book {
public:
Book(const std::string& title, const std::string& author)
: title(title), author(author) {
std::cout << "Book created: " << title << " by " << author << std::endl;
}
~Book() {
std::cout << "Book destroyed: " << title << " by " << author << std::endl;
}
void display() const {
std::cout << "Title: " << title << ", Author: " << author << std::endl;
}
private:
std::string title;
std::string author;
};
Step 2: Using std::unique_ptr
Create a Book using std::unique_ptr. You should create a unique_ptr for a book, display its information, and ensure that it is automatically deleted when it goes out of scope.
void useUniquePtr() {
std::unique_ptr<Book> uniqueBook = std::make_unique<Book>("1984", "George Orwell");
uniqueBook->display();
// uniqueBook will be automatically destroyed when it goes out of scope
}
Exercise:
- Run the program and verify that the book is created and destroyed properly.
Step 3: Using std::shared_ptr
Now, create a Book using std::shared_ptr. You will create multiple shared pointers pointing to the same Book object. Ensure that the object is deleted when the last shared pointer goes out of scope.
void useSharedPtr() {
std::shared_ptr<Book> sharedBook1 = std::make_shared<Book>("To Kill a Mockingbird", "Harper Lee");
std::shared_ptr<Book> sharedBook2 = sharedBook1; // shared ownership
sharedBook1->display();
sharedBook2->display();
// sharedBook1 and sharedBook2 will be automatically destroyed when they go out of scope
}
Exercise:
- Create a second
shared_ptr that shares ownership of the same book.
- Observe the reference count behavior (you can print the reference count if you want).
- Check that the book is destroyed only after the last shared pointer goes out of scope.
Step 4: Using std::weak_ptr
Use a std::weak_ptr to observe a Book managed by std::shared_ptr, but without affecting its reference count. The purpose of weak_ptr is to avoid circular references.
void useWeakPtr() {
std::shared_ptr<Book> sharedBook = std::make_shared<Book>("The Catcher in the Rye", "J.D. Salinger");
std::weak_ptr<Book> weakBook = sharedBook; // weak_ptr does not affect reference count
if (auto lockedBook = weakBook.lock()) {
lockedBook->display();
} else {
std::cout << "The book has been deleted." << std::endl;
}
// The book will be destroyed after the last shared_ptr goes out of scope
}
Exercise:
- Use
weak_ptr to observe the shared_ptr-managed book.
- Try to lock the
weak_ptr and display the book’s information.
- After the last
shared_ptr is destroyed, try locking the weak_ptr again to observe that the book is no longer available.
Step 5: Putting it All Together
Now, in your main function, use the functions to demonstrate the three types of smart pointers:
int main() {
std::cout << "Using unique_ptr:\n";
useUniquePtr();
std::cout << "\nUsing shared_ptr:\n";
useSharedPtr();
std::cout << "\nUsing weak_ptr:\n";
useWeakPtr();
return 0;
}
Step 6: Test and Observe the Output
Run the program, and observe the following:
unique_ptr: You should see that the book is created and destroyed automatically, with no extra output beyond the creation and destruction messages.shared_ptr: You’ll observe that the book is created and destroyed once the last shared_ptr goes out of scope.weak_ptr: You’ll see how weak_ptr can observe an object without affecting its lifetime. When the shared_ptr is destroyed, the book is deleted, and you won’t be able to lock the weak_ptr anymore.
Additional Challenges:
- Reference Counting: Print the reference count of a
shared_ptr at different points in your program using std::shared_ptr::use_count().
- Circular References: Try creating a scenario where two
shared_ptrs reference each other (a circular reference). Use weak_ptr to fix the issue and prevent a memory leak.
- Custom Deleter: Experiment with using a custom deleter when creating smart pointers (e.g., deleting an object via a specific function instead of
delete).
Conclusion
By completing this exercise, you’ll have a deeper understanding of how smart pointers work in C++, including ownership semantics and memory management. You’ll also gain experience in how unique_ptr, shared_ptr, and weak_ptr can be used to manage resources safely and efficiently in a C++ program.
Would it be possible to have some sort of framework through which chatgpt generated exercises can be added to exercism?
I really don’t want to sound too critical but we do live in the era of chatgpt and some attention needs to given to providing value beyond what chatgpt provides. Otherwise we are all publishing phone books in the era of the internet.
