The evolution of C++ was fundamentally driven by the introduction of objects; in fact, the language was originally titled "C with Classes". In modern software development, a class serves as the definition or blueprint for an object, acting as a user-defined type similar to an int. An object, conversely, is the actual variable instantiated from that class type.
Encapsulation and Access Control
One of the primary distinctions between a struct and a class in C++ is the default access level: while struct members are public by default, all class members are private unless specified otherwise. To allow interaction with an object, developers use the public: directive.
Best practices suggest keeping data private and using accessor functions—such as SetPage() or GetCurrentPage()—to manipulate object variables. This promotes encapsulation and prevents unauthorized external access to internal data.
Example: The Book Class
class Book {int PageCount; // Private memberint CurrentPage; // Private memberpublic:Book(int NumPages); // Constructor~Book() {}; // Destructorvoid SetPage(int PageNumber); // Accessor functionint GetCurrentPage(void); // Accessor function};// Definition using the :: scope identifiervoid Book::SetPage(int PageNumber) {CurrentPage = PageNumber;}
The Object Lifecycle: Constructors and Destructors
A constructor is a specialized function with the same name as the class that is called automatically when an object is created. Its primary role is to initialize class members. While the compiler will provide a default constructor if none is declared, providing a custom constructor with parameters prevents the compiler from generating that default.
A destructor is identified by the tilde (~) prefix and is called when an object goes out of scope or is terminated. Its purpose is to "tidy up" by releasing resources like memory or file handles.
Inheritance and the Power of Polymorphism
Inheritance allows for the creation of a derived class that inherits all members from a base class. This hierarchy is essential for polymorphism, which refers to the ability of different objects to respond to the same function call in unique ways. This is achieved using virtual functions.
Example: Inheritance and Virtual Functions
class Point {int x, y;public:Point(int atx, int aty);virtual ~Point(); // Virtual destructor for proper cleanupvirtual void Draw(); // Virtual function for polymorphism};class Circle : public Point {int radius;public:// Using an initializer list to call the base constructorCircle(int atx, int aty, int r) : Point(atx, aty) {radius = r;}virtual void Draw(); // Overriding the base function};
Advanced Resource Management
When working with inheritance, professional C++ development requires making destructors virtual. If a destructor is virtual, the compiler ensures that the most derived class's destructor is called first, followed by its ancestors in reverse order. This sequence is critical for preventing memory leaks when derived classes use dynamic variables like pointers.
Furthermore, for small, frequently called functions, developers may use inline functions. These act as hints to the compiler to insert the function code directly at the call site, which can significantly improve performance when used within loops.
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