In C++ function call semantics, what is meant by early binding, and how does early binding differ from late (dynamic) binding when resolving which function implementation to execute?

Introduction / Context:
Early binding is the counterpart of late binding in C++ function dispatch. While late binding applies to virtual functions and uses the dynamic type of objects at runtime, early binding applies to most ordinary function calls and is resolved entirely at compile time. Understanding this distinction is important for predicting performance characteristics and behaviour of member function calls in C++ programs.

Given Data / Assumptions:

• We have classes with both nonvirtual and virtual member functions.
• Calls are made through objects or pointers that may be of base or derived class types.
• The compiler may either resolve calls at compile time (early binding) or generate runtime dispatch (late binding).
• The question asks for the definition of early binding and how it differs from late binding.

Concept / Approach:
Early binding means that the compiler decides which function body will be called based on the static type information available in the source code. For nonvirtual functions, calls are bound early; the compiler generates a direct call to a specific function address, possibly allowing inlining and other optimisations. In contrast, late binding defers this decision to runtime. The correct option should emphasise compile time resolution based on static type, particularly for nonvirtual functions.

Step-by-Step Solution:
Step 1: Recall that a nonvirtual member function call like obj.func() or ptr->func() is resolved by the compiler using the static type of obj or ptr. Step 2: The compiler knows exactly which function implementation to call and generates a direct call instruction in the compiled code. Step 3: This compile time decision is early binding. Step 4: Check option (a), which states that early binding means the implementation is determined at compile time using the static type, which matches the definition. Step 5: Compare with other options, which either mix up runtime behaviour or discuss unrelated features like reflection, which is not part of core C++.

Verification / Alternative check:
To verify, imagine a simple class with two nonvirtual functions: void f(); and void g(); When you write obj.f();, the compiler knows at compile time that obj is of class MyClass and that MyClass::f must be called. It emits the corresponding call. If later you derive from MyClass but do not make f virtual, calling f through a base pointer still calls MyClass::f, because the binding was decided early. This behaviour shows that early binding uses static type information and does not change at runtime, confirming option (a).

Why Other Options Are Wrong:
Option (b) incorrectly suggests that binding happens only when the program starts running; in reality, early binding decisions are made during compilation. Option (c) is wrong because header declarations and prototypes are about compilation and name resolution, not binding behaviour. Option (d) describes dynamic lookup via reflection, which is not how early binding works and not a core feature of C++ for normal functions.

Common Pitfalls:
A common pitfall is to assume that declaring a function inside a class automatically makes it virtual and subject to late binding. In C++, functions are nonvirtual by default and therefore use early binding unless explicitly declared virtual. Another mistake is to believe that early binding and late binding are performance synonyms; early binding usually allows more optimisation and avoids the overhead of virtual dispatch, which is why some performance critical code avoids unnecessary virtual functions.

Final Answer:
Early binding means that the function implementation to be called is determined at compile time based on the static type of the object or pointer, as happens for nonvirtual functions.