Grab the file arraysWork.cpp.

Question

It will not compile as it has some errors in it. Feel free to remove them when you are working on the code. Your goal is to comment on every single line in the function main except for the return statement with what is being done in this line; for print statements, place what values you see and what these values represent. The lines with errors also must be commented on, so don't forget to return them. What is attempted to be done in the code, and why is it an error?

#include<iostream>

#include<memory>

using std::unique_ptr;

using std::cout;

using std::endl;

int main()

{

int a{ 10 }, b{ 20 };

unique_ptr<int> ap{new int};

*ap = 23;

cout << ap << endl;

cout << *ap << endl;

ap.release();

cout << ap << endl;

unique_ptr<int> ap2 = &a;

unique_ptr<int> ap3{ new int };

*ap3 = 12;

unique_ptr<int> ap4{ new int };

*ap4 = 14;

ap4 = ap3;

return 0; // no need to comment on this line

}

Answer 1

Here are the errors I see in the code:

1. Line 18: unique_ptr<int> ap2 = &a;
2. Error: Attempting to assign the address of a stack-allocated variable (a) to a unique_ptr<int>.
3. Solution: You cannot assign the address of a stack-allocated variable to a unique_ptr. Instead, you should allocate memory using new int to initialize ap2.
4. Line 24: cout << ap << endl;
5. Error: Printing the memory address stored in ap instead of the value it points to.
6. Solution: Change cout << ap to cout << *ap to print the value stored in the memory location pointed by ap.
7. Line 27: ap.release();
8. Error: Releasing ownership of the dynamically allocated memory without assigning it to another smart pointer or deallocating it.
9. Solution: If you intend to release the ownership, make sure you have another smart pointer taking ownership of the memory or use delete ap to deallocate the memory explicitly.

Here's the corrected code with the errors fixed:

#include <iostream>

#include <memory>

using std::unique_ptr;

using std::cout;

using std::endl;

int main()

{

int a{ 10 }, b{ 20 }; // Declaring and initializing variables a and b with values 10 and 20, respectively

unique_ptr<int> ap = std::make_unique<int>(); // Creating a unique_ptr object named ap and dynamically allocating an integer with make_unique

*ap = 23; // Assigning the value 23 to the memory location pointed by ap

cout << *ap << endl; // Printing the value stored in the memory location pointed by ap, which is 23

ap.release(); // Releasing the ownership of the dynamically allocated memory pointed by ap

cout << ap << endl; // Printing the value of ap, which is nullptr after releasing the ownership

unique_ptr<int> ap2 = std::make_unique<int>(a); // Creating a unique_ptr object named ap2 and dynamically allocating an integer with make_unique, initializing it with the value of a (10)

unique_ptr<int> ap3 = std::make_unique<int>(); // Creating a unique_ptr object named ap3 and dynamically allocating an integer with make_unique

*ap3 = 12; // Assigning the value 12 to the memory location pointed by ap3

unique_ptr<int> ap4 = std::make_unique<int>(); // Creating a unique_ptr object named ap4 and dynamically allocating an integer with make_unique

*ap4 = 14; // Assigning the value 14 to the memory location pointed by ap4

ap4 = std::move(ap3); // Transferring the ownership of the memory pointed by ap3 to ap4 using std::move and releasing the previously allocated memory pointed by ap4

return 0;

}

Instead of using new int to dynamically allocate memory for the unique_ptr objects, it is recommended to use std::make_unique<int>(). This is a safer and more concise way to allocate memory for a unique_ptr and initialize the object.