Unary/Binary Operator Overloading, Stream Insertion/Extraction & Type Conversions

Explanation

Operator overloading transforms user-defined classes into first-class mathematical types without changing operator precedence or associativity. When overloading binary operators as member functions, the left operand is implicitly *this and the right operand is passed as an argument. Overloading via friend functions is necessary to support commutative operations where a primitive appears on the left (e.g., 5 + myObject).

Key points

• Operators that CANNOT be overloaded: . (member access), .* (pointer-to-member), :: (scope resolution), ?: (ternary conditional), sizeof.
• Prefix vs Postfix ++/--: Prefix takes no argument (operator++()); Postfix takes a dummy int argument (operator++(int)).
• Overloading stream operators: operator<< and operator>> MUST be overloaded as friend functions because the left-hand operand is an ostream/istream reference.
• Type Conversions: (1) Basic to Class type (via single-argument constructor), (2) Class to Basic type (via operator type() conversion function), (3) Class to Class type.

Example

Code examples

// Overloading Binary + and Stream Insertion <<
#include <iostream>
using namespace std;

class Vector2D {
private:
    float x, y;

public:
    Vector2D(float x = 0, float y = 0) : x(x), y(y) {}

    // Overloading binary + as member function
    Vector2D operator+(const Vector2D &other) const {
        return Vector2D(this->x + other.x, this->y + other.y);
    }

    // Overloading prefix ++
    Vector2D& operator++() {
        ++x; ++y;
        return *this;
    }

    // Overloading postfix ++
    Vector2D operator++(int) {
        Vector2D temp = *this;
        x++; y++;
        return temp;
    }

    // Overloading << as friend function
    friend ostream& operator<<(ostream &out, const Vector2D &v) {
        out << "(" << v.x << ", " << v.y << ")";
        return out;
    }
};

Exam questions

• [8 Marks] Overload the stream insertion (<<) and extraction (>>) operators for a Matrix or Complex number class in C++.
• [7 Marks] Differentiate between prefix and postfix increment operator overloading with code examples.
• [7 Marks] Explain data conversion routines: (i) Basic to Class type, (ii) Class to Basic type, (iii) Class to another Class type with examples.