Day 47: Xerox vs Original Notes Oops (Part 4)

📅 Date: Feb 16, 2026

🧠 Mood: Genetic Engineer 🧬

🔥 Topic: OOPs Part 4: Copy Constructor (Shallow vs Deep)

👯 Cloning an Object

Imagine you have a Hero object named "Superman" with 100 HP. Now you want to create another hero "Clone_Superman" with the exact same stats.

Instead of setting values manually again, we can Copy the first object. This is where the Copy Constructor comes in.

Hero h1(100);      // Original
Hero h2 = h1;      // Copy Created! (Copy Constructor Called)

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⚠️ The Trap: Shallow vs Deep Copy

This is the most asked Interview Question in OOPs.

1. Shallow Copy (The Default)

Imagine Student A has a Notebook. Student B wants to copy. In Shallow Copy, Student B doesn't buy a new notebook. He just holds Student A's notebook.

❌ The Problem: If Student A tears a page, Student B's page is also gone! (Because they share the same memory address).

2. Deep Copy (The Solution)

Student B buys a New Notebook and writes everything down from Student A's notebook.

✅ The Benefit: If Student A tears a page, Student B is safe. They have separate memory.

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💻 Defining a Copy Constructor

By default, C++ does a Shallow Copy. If you want Deep Copy (usually when using Pointers), you have to write your own Copy Constructor.

class Hero {
    public:
    int health;
    int level;

    // 1. Simple Constructor
    Hero(int h, int l) {
        health = h;
        level = l;
    }

    // 2. Custom COPY Constructor
    // Syntax: ClassName(const ClassName &obj)
    Hero(const Hero &temp) {
        cout << "⚙️ Copy Constructor Called!" << endl;
        this->health = temp.health;
        this->level = temp.level;
    }
    
    void print() {
        cout << "Health: " << health << " Level: " << level << endl;
    }
};

int main() {
    Hero h1(100, 5);
    h1.print();

    // Copying h1 to h2
    Hero h2(h1); 
    // OR: Hero h2 = h1;
    
    h2.print(); // Prints same values as h1

    return 0;
}

💡 Why pass by Reference `&temp`?

If we pass by value Hero temp, it will create a copy. To create a copy, it will call Copy Constructor again. This will create an Infinite Loop! That's why we always pass by Reference &.

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🚀 Day 47 Challenge

1. Create a class Book with pages.
2. Create an object b1 with 500 pages.
3. Create b2 by copying b1.
4. Print "Book Copied Successfully!".
5. Bonus: Try to remove & from the copy constructor arguments and see the error.

Next Up: Day 48 - Inheritance (The Family Tree of Code).