Introduction to Classes recap

Excellent work! You've learned the fundamentals of object-oriented programming in C++. Let's review the key concepts from this section.

Object-Oriented Programming

Object-oriented programming (OOP) combines data and the functions that operate on that data into unified types called classes. This approach better models real-world concepts compared to procedural programming, where data and functions are separate.

Classes and Objects

A class is a program-defined type that bundles data members (variables) and member functions (methods). An object (or instance) is a variable of a class type. Each object has its own copy of the class's data members.

Member Functions

Member functions provide behaviors for class objects. They have implicit access to the object they're called on and can call other member functions of the same class.

Access Specifiers

C++ provides three access levels:

  • public: Accessible from anywhere
  • private: Accessible only within the class
  • protected: Accessible within the class and derived classes

Class members are private by default; struct members are public by default.

Encapsulation

Encapsulation hides implementation details behind a public interface. This protects object integrity, enables implementation changes without affecting users, simplifies debugging, and prevents misuse.

Access Functions

Getters retrieve private member values; setters modify them. Access functions enable validation, computed properties, side effects during changes, and future flexibility.

Constructors

Constructors are special member functions that initialize objects when they're created. They have the same name as the class and no return type.

Member Initializer Lists

Member initializer lists directly initialize members before the constructor body runs, providing better efficiency than assignment. They're required for const members, reference members, and members without default constructors.

Default Constructors

A default constructor can be called with no arguments. If you define any constructor, you must explicitly provide a default constructor if you want one. Use = default to request the compiler-generated version.

Delegating Constructors

One constructor can delegate to another, reducing code duplication and centralizing initialization logic.

Copy Constructors

The copy constructor creates new objects as copies of existing ones. Provide custom copy constructors when your class manages resources to perform deep copying instead of shallow copying. Delete the copy constructor (= delete) for uncopyable types.

Copy Elision

The compiler can eliminate unnecessary copy operations through optimizations like Return Value Optimization (RVO). Trust these optimizations and write natural code.

Temporary Objects

Temporaries are unnamed objects created for single expressions. They're destroyed at the end of the statement unless bound to const references, which extends their lifetime.

Converting Constructors and explicit

Constructors taking one argument enable implicit conversions. Mark them explicit to prevent unexpected conversions and make code intentions clear.

constexpr Classes

Classes can have constexpr constructors and member functions, enabling compile-time object creation and function evaluation for improved performance and type safety.

Key Terminology

  • Class: Program-defined type combining data and functions
  • Object/Instance: Variable of a class type
  • Member variable/Data member: Variable defined in a class
  • Member function/Method: Function defined in a class
  • Access specifier: Keyword controlling member visibility (public, private, protected)
  • Encapsulation: Hiding implementation details behind a public interface
  • Getter/Accessor: Function that retrieves a private member's value
  • Setter/Mutator: Function that modifies a private member's value
  • Constructor: Special function that initializes objects
  • Member initializer list: Syntax for directly initializing members
  • Default constructor: Constructor callable with no arguments
  • Delegating constructor: Constructor that calls another constructor
  • Copy constructor: Constructor that creates copies of objects
  • Copy elision: Compiler optimization eliminating unnecessary copies
  • Temporary object: Unnamed object created for a single expression
  • Converting constructor: Constructor enabling implicit type conversion
  • explicit keyword: Prevents implicit conversions
  • constexpr: Enables compile-time evaluation

Design Principles

Prefer private members: Keep data members private and provide access through public member functions.

Make interfaces minimal: Only expose what users truly need.

Initialize in member initializer lists: More efficient than assignment in constructor bodies.

Mark functions const: Const member functions document read-only operations and work with const objects.

Use explicit for single-argument constructors: Prevent surprising implicit conversions.

Provide copy constructors for resource-managing classes: Ensure proper deep copying.

Trust compiler optimizations: Return local objects by value without worrying about performance.

Looking Forward

You've built a strong foundation in object-oriented C++. Future topics will expand on these concepts:

  • Destructors for cleanup when objects are destroyed
  • Operator overloading for natural syntax with custom types
  • Inheritance for building class hierarchies
  • Polymorphism for runtime behavior selection
  • Move semantics for efficient resource transfer
  • Smart pointers for automatic memory management

Object-oriented programming is central to modern C++. The principles you've learned—encapsulation, proper initialization, const correctness—will serve you throughout your C++ journey. Practice applying these concepts to solidify your understanding and develop good design habits.