In C++ polymorphism, what is meant by dynamic binding, and how does it affect which function implementation is called at runtime when using base class pointers or references?

Introduction / Context:
Polymorphism is a central concept in C++ object oriented programming, and dynamic binding is the mechanism that enables polymorphic behaviour at runtime. Understanding dynamic binding is crucial for designing class hierarchies, using virtual functions, and predicting which function implementation will actually run when calling through a base class pointer. This question aims to check your conceptual understanding of dynamic binding in C++.

Given Data / Assumptions:

• We have a base class with at least one virtual function.
• There are one or more derived classes that override this virtual function.
• We use a base class pointer or reference to refer to objects that may actually be instances of derived classes.
• The question is about when the decision of which function body to execute is made.

Concept / Approach:
Dynamic binding, also called late binding or runtime polymorphism in C++, occurs when the binding between a function call and the function implementation happens at runtime based on the object's dynamic type. This happens for virtual functions when they are called through a base class reference or pointer. The compiler generates code that uses a virtual function table (vtable) or a similar mechanism to look up the correct function implementation at runtime. The correct option should emphasise runtime selection based on dynamic type for virtual functions.

Step-by-Step Solution:
Step 1: Recall that in C++, nonvirtual functions are bound statically at compile time based on the static type of the object or pointer. Step 2: Remember that when a function is declared virtual in a base class and overridden in a derived class, calls made through a base pointer or reference may dispatch to the derived implementation. Step 3: Recognise that the actual function chosen is determined at runtime using the object's dynamic type, which is the essence of dynamic binding. Step 4: Examine option (a), which correctly describes dynamic binding as selecting the function at runtime based on the actual type when calling virtual functions. Step 5: Confirm that other options talk about compile time inlining, link time decisions, or source code editors, which are unrelated to C++ runtime polymorphic dispatch.

Verification / Alternative check:
To verify, consider classes Shape, Circle, and Rectangle, where Shape has a virtual draw function and Circle and Rectangle override it. If you write Shape *p = new Circle(); and later call p->draw();, the function that executes is Circle::draw, not Shape::draw, even though p is of type Shape *. The decision is made at runtime using the virtual table, which demonstrates dynamic binding in action and matches the description in option (a).

Why Other Options Are Wrong:
Option (b) is wrong because inlining is a compile time optimisation that actually removes function call overhead rather than making dispatch dynamic. Option (c) is incorrect because link time binding is still static; the choice of function implementation does not change at runtime. Option (d) is unrelated to C++ language semantics and instead refers to tooling behaviour in an editor.

Common Pitfalls:
A common pitfall is to assume that all member function calls use dynamic binding. In C++, only virtual functions called through a base class reference or pointer participate in dynamic binding by default. Another mistake is to confuse dynamic binding with dynamic linking of libraries; these are different concepts. Understanding that dynamic binding is about runtime decision of which virtual function body to execute is key to building correct polymorphic designs.

Final Answer:
Dynamic binding means that the function to be executed is selected at runtime based on the actual (dynamic) type of the object when calling virtual functions through base class pointers or references.