C++ Classes

Theory

Classes in C++ are the foundation of object-oriented programming. They define the blueprint for objects with data members and member functions.

Defining Classes and Constructors

class Point {
private:
    double x, y;
 
public:
    Point() : x(0), y(0) {}  // Default constructor
 
    Point(double x, double y) : x(x), y(y) {}  // Parameterized
 
    double getX() const { return x; }
    double getY() const { return y; }
};

Initializer lists (: x(x), y(y)) are preferred over assignment in the constructor body — they are more efficient and necessary for const/reference members.

Destructors

A destructor (~ClassName) runs when an object is destroyed. It is essential for RAII — releasing resources automatically:

class FileHandler {
    FILE* file;
public:
    FileHandler(const char* name) { file = fopen(name, "r"); }
    ~FileHandler() { if (file) fclose(file); }
};

The this Pointer

this is a pointer to the current object instance. It resolves naming conflicts and enables method chaining:

class Person {
    std::string name;
public:
    Person& setName(const std::string& name) {
        this->name = name;
        return *this;
    }
};

Friend Functions

A friend function can access private members of a class even though it is not a member:

Static Members

Static members belong to the class itself, not to individual objects. They must be defined outside the class:

class Counter {
    static int count;
public:
    Counter() { count++; }
    static int getCount() { return count; }
};
int Counter::count = 0;

Const Correctness

Mark member functions as const when they don't modify the object. This allows them to be called on const objects and references.

Practical Examples

Exercises

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