Introduction to Constructors in C++

Constructors are special member functions in C++ that are automatically called when an object of a class is created. They are used to initialize the data members of an object and perform any necessary setup.

Syntax

C++

class MyClass {
public:
    MyClass() {
        // Constructor body
    }
};

Types of Constructors

1. Default Constructor: A constructor with no parameters. It is automatically generated by the compiler if no other constructors are defined.

2. Parameterized Constructor: A constructor that takes parameters to initialize the data members of the object.

3. Copy Constructor: A constructor that takes an object of the same class as a parameter and creates a copy of that object.

Example: Default Constructor

#include <iostream>

using namespace std;

class Person {
public:
    string name;
    int age;

    Person() {
        cout << "Default constructor called" << endl;
    }
};

int main() {
    Person p1; // Default constructor is called

    return 0;
}

Output:

Default constructor called

Example: Parameterized Constructor

#include <iostream>

using namespace std;

class Person {
public:
    string name;
    int age;

    Person(string name, int age) {
        this->name = name;
        this->age = age;
    }
};

int main() {
    Person p2("Alice", 25);

    cout << "Name: " << p2.name << endl;
    cout << "Age: " << p2.age << endl;

    return 0;
}

Output:

Name: Alice
Age: 25

Example: Copy Constructor

#include <iostream>

using namespace std;

class Person {
public:
    string name;
    int age;

    Person(string name, int age) {
        this->name = name;
        this->age = age;
    }

    Person(const Person& other) {
        name = other.name;
        age = other.age;
    }
};

int main() {
    Person p3("Bob", 30);
    Person p4 = p3; // Copy constructor is called

    cout << "p4.name: " << p4.name << endl;
    cout << "p4.age: " << p4.age << endl;

    return 0;
}

Output:

p4.name: Bob
p4.age: 30

Key Points:

• Constructors are used to initialize objects.

• Default constructors are automatically generated if not defined.

• Parameterized constructors take parameters to initialize data members.

• Copy constructors are used to create copies of objects.

• The this pointer can be used to refer to the current object within a member function.

By understanding constructors, you can effectively initialize objects and control their creation in C++.