C++ Const Member Variable Initialization In Constructor

3 min read Jul 01, 2024

C++ const Member Variable Initialization in Constructor

In C++, const member variables cannot be directly assigned values within the class definition. This is because const members are meant to hold constant values throughout the object's lifetime, and their values must be initialized during object creation.

Here's how you can initialize const member variables in C++ constructors:

Initialization List

The most common and recommended way is using an initialization list in the constructor. This technique guarantees that the const member variable is initialized before the constructor body executes.

#include 

class MyClass {
public:
  MyClass(int value) : constValue(value) { // Initialization list
    std::cout << "constValue: " << constValue << std::endl; 
  }

private:
  const int constValue; 
};

int main() {
  MyClass obj(10); // Initialize constValue to 10 during object creation
}

Explanation:

const int constValue;: We declare constValue as a const member variable of type int.
MyClass(int value) : constValue(value): The constructor takes an integer value as an argument. In the initialization list, we initialize constValue using the constructor parameter value.

Why Initialization List?

Initialization order: The initialization list ensures that constValue is initialized before the constructor body executes. This is crucial for maintaining the integrity of the const member.
Efficiency: Using the initialization list is generally considered more efficient than assigning the value inside the constructor body.

Important Points

No assignment: You cannot assign values to const members inside the constructor body.
Static const members: Static const members can be initialized directly within the class definition, as they are initialized once during program startup.

By understanding how to initialize const member variables in constructors, you can effectively leverage their immutability and maintain a clean and robust class design in your C++ projects.

C++ Const Member Variable Initialization In Constructor