Copy Constructor

A copy constructor is a special constructor in C++ that creates a new object as a copy of an existing object.

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🔑 Definition:

It takes a reference to another object of the same class as its parameter.

ClassName(const ClassName &obj) {
    // Copy code here
}

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✅ Purpose of Copy Constructor

• To create a new object with the same values as an existing one.
• Helps in copying objects safely, especially when dealing with pointers or dynamic memory.
• Used when:
  • Passing an object by value to a function.
  • Returning an object from a function.
  • Initializing one object with another.

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🔧 Example: Simple Copy Constructor

#include <iostream>
using namespace std;

class Student {
    int roll;
    string name;

public:
    // Parameterized Constructor
    Student(int r, string n) {
        roll = r;
        name = n;
    }

    // Copy Constructor
    Student(const Student &s) {
        roll = s.roll;
        name = s.name;
    }

    void display() {
        cout << "Roll No: " << roll << ", Name: " << name << endl;
    }
};

int main() {
    Student s1(101, "Alice");  // Original object
    Student s2 = s1;           // Copy constructor is called

    cout << "Original: ";
    s1.display();

    cout << "Copied: ";
    s2.display();

    return 0;
}

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🎯 Output:

Original: Roll No: 101, Name: Alice  
Copied: Roll No: 101, Name: Alice

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💡 Key Features

Feature	Description
Name	Same as class name
Parameter	Takes a reference to another object
When Called	On object copy or passing/returning objects
Implicit Version	C++ provides a default copy constructor
Custom Version	Needed when deep copy is required

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🧠 Shallow vs. Deep Copy

🧪 Shallow Copy:

• Copies memory address (pointer).
• Both objects share the same memory.
• Can cause issues when one object changes the shared data or deletes it.

🧪 Deep Copy:

• Copies actual data, not just the pointer.
• Each object has its own copy.
• Prevents unwanted changes and memory errors.

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🛑 Example of the Need for Deep Copy

If your class contains pointers or uses new, a custom copy constructor is necessary to create a deep copy.

class Example {
    int* data;

public:
    Example(int val) {
        data = new int(val);  // Dynamic memory
    }

    // Custom Copy Constructor for Deep Copy
    Example(const Example &obj) {
        data = new int(*obj.data);  // New memory allocation
    }

    ~Example() {
        delete data;  // Prevent memory leak
    }
};

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🧾 Summary

• A copy constructor creates a new object by copying another object.
• Syntax: ClassName(const ClassName &obj)
• Used for:
  • Copying objects
  • Passing objects by value
  • Returning objects from functions
• Use a custom copy constructor when dealing with pointers or dynamic memory.