Initialize const Variable Using Member Initializer List in C++

1️⃣ Why Use Member Initializer List for const Variables?

A const variable in a class must be initialized at the time of object creation, and it cannot be assigned later.
✔ Member Initializer List is required because we cannot modify const values inside the constructor body.
✔ Prevents accidental modification after initialization.

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2️⃣ Syntax

class ClassName {
private:
    const int value;  // Constant member

public:
    ClassName(int v) : value(v) {  // Member Initializer List
    }
};

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3️⃣ Example: Initializing a const Variable

#include <iostream>
using namespace std;

class Test {
private:
    const int x;  // Constant variable

public:
    // Member Initializer List to initialize const variable
    Test(int val) : x(val) {
        cout << "x = " << x << endl;
    }
};

int main() {
    Test obj(10);  // Initializing const member

    return 0;
}

🔹 Output

x = 10

✅ Why is Member Initializer List needed here?
✔ const int x cannot be assigned inside the constructor body, so we initialize it in the initializer list.

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4️⃣ Example: Initializing Multiple const Members

#include <iostream>
using namespace std;

class Constants {
private:
    const int a;
    const double b;

public:
    Constants(int x, double y) : a(x), b(y) {
        cout << "a = " << a << ", b = " << b << endl;
    }
};

int main() {
    Constants obj(5, 3.14);

    return 0;
}

🔹 Output

a = 5, b = 3.14

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5️⃣ Example: Initializing const in Derived Class (Inheritance)

#include <iostream>
using namespace std;

class Base {
protected:
    const int baseValue;

public:
    // Initializing const in Base class
    Base(int val) : baseValue(val) {
        cout << "Base Value = " << baseValue << endl;
    }
};

class Derived : public Base {
private:
    const int derivedValue;

public:
    // Initializing const in both Base and Derived classes
    Derived(int b, int d) : Base(b), derivedValue(d) {
        cout << "Derived Value = " << derivedValue << endl;
    }
};

int main() {
    Derived obj(10, 20);

    return 0;
}

🔹 Output

Base Value = 10
Derived Value = 20

✅ Key Points:
✔ const baseValue is initialized in Base class initializer list.
✔ const derivedValue is initialized in Derived class initializer list.

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6️⃣ Key Takeaways

✔ Member Initializer List is required for const variables because they cannot be modified later.
✔ Ensures efficiency & proper initialization.
✔ Works in both single and multiple inheritance scenarios.

Would you like an example with reference members (&) and const together? 🚀