In-Depth Notes on Copy and Assignment in C++

Unit 5b – Copy and Assignment

Introduction

• Overview of copy constructors and assignment in C++.
• Understanding the roles of this pointer and member functions.

The this Pointer

• Purpose: Allows member functions to refer to the object calling them.
  • Each member function has a hidden parameter this, which is a pointer to the instance of the object.
  • Example:
    cpp void Deck::shuffle() { this->cut(); // calls cut() on the current object }

Distinguishing Between Member Variables and Parameters

• Name Conflicts: When parameters and member variables share the same name, use this to resolve ambiguity.
  • Example Class Definition:
    cpp class Student { public: Student(string name, int id, double gpa); private: string name; int id; double gpa; }; Student::Student(string name, int id, double gpa) { this->name = name; // Clarity in assignment }

Copying Objects

• Member-by-Member Copy: When assigning one object to another, a member-by-member copy occurs.
  • Example:
    cpp student s1, s2; s2 = s1; // Copies contents of s1 to s2

Copy Constructors

• Purpose: Creates a new object as a copy of an existing object.
  • Must define a custom copy constructor for a deep copy.
  • Signature:
    cpp Complex(const Complex& rhs);
  • Implicit Call: The copy constructor is called when passing by value or initializing a new object.
    cpp Complex c3(c1); // Copy constructor invoked

Assignment Operators

• Definition: The function that handles assignment of one object to another already existing object.
  • Signature:
    cpp Complex& operator=(const Complex& other);
  • Handles self-assignment and freeing old memory to avoid leaks.
  • Chaining Assignment: Returns *this to allow chaining.
    cpp c4 = c3 = c2;

Shallow vs. Deep Copies

• Shallow Copy: Only copies the values of data members, not the data they point to.
  • Default copy constructors/assignment operators perform shallow copies.
• Deep Copy: Every additional data pointed to is also copied, necessary when using dynamic memory allocation.

Rule of Three

• If a class requires a non-default destructor, copy constructor, or assignment operator, it likely needs all three due to resource management needs.

Implementation Practice

• Implement -= operator for list removal, == operator for list comparison, and write copy constructor and assignment operator for custom classes as an exercise.

Summary and Review

• Review key concepts of copy assignment and copy constructors, considerations for memory management, and practical applications in creating and managing objects in C++.

Final Points

• Reinforce understanding through exercises that enforce knowledge of the copy constructor, assignment operator, and using this pointer correctly in C++.