Understanding the Difference Between Reference and Non-Reference Members in a Class

When declaring a member variable in a class, you have the option to declare it as a reference or as a non-reference. Understanding the difference between these two types is crucial, as it affects how they are initialized within the class.

Let’s dive into the dissimilarities between reference and non-reference members through an illustrative example:

class MyClass {
public:
    MyClass(int& ref_val, int non_ref_val) : ref_val_(ref_val), non_ref_val_(non_ref_val) {}

private:
    int& ref_val_;
    int non_ref_val_;
};

int main() {
    int x = 42; 
    MyClass my_class(x, 10);
    return 0;
}

In the given example, we define a class called MyClass featuring two member variables: ref_val_, a reference to an integer, and non_ref_val_, a regular integer.

The key disparity arises in the constructor. The ref_val_ member is initialized in the constructor’s initialization list using the argument ref_val, which is a reference to an integer. This step is essential since a reference must be initialized upon declaration.

One practical application of using reference members is when we want to associate an external object with the class without initializing it inside the class constructor. By initializing the reference member outside the class, we can control the lifetime and initialization of the referenced object separately.

However, it’s crucial to ensure that the lifetime of the referenced object extends beyond the lifetime of the object holding the reference. In this case, if x is going to be used in MyClass, you should ensure that x remains in scope for the entire duration of my_class‘s lifetime. Failure to do so may lead to undefined behavior.

Understanding the difference between reference and non-reference members helps you make informed decisions when designing your classes and ensures the proper usage and management of references within your codebase. It provides flexibility in managing object lifetimes and improves the overall design of your C++ classes.