When you do not explicitly declare any constructors for a C++ class, which translation stage will implicitly declare a default (zero-argument) constructor if eligible?

Introduction / Context:
C++ supports implicitly-declared special member functions to simplify class usage. One is the default constructor, which enables default-initialization of objects when no user-declared constructors exist. This question asks which stage is responsible for creating it.

Given Data / Assumptions:

• No constructors are declared by the programmer.
• We consider standard compilation pipeline roles.
• Eligibility rules for implicit declaration are satisfied.

Concept / Approach:
The compiler analyzes class definitions and, if the rules allow, implicitly declares a default constructor. The preprocessor only handles macros and includes; the linker and loader deal with binary combination and loading; neither invents C++ class members. Hence, the compiler is the correct answer.

Step-by-Step Solution:
1) Write class C {}; with no constructors.2) The compiler implicitly declares C::C().3) You can then write C c; and it compiles.4) If you declare any constructor, the implicit default constructor is no longer provided automatically unless you write C() = default;.

Verification / Alternative check:
Inspect error messages when adding a parameterized constructor but forgetting to add a default one; the compiler will note that C is not default-constructible.

Why Other Options Are Wrong:
Preprocessor/linker/loader: not responsible for generating C++ class members.Run-time library: does not declare constructors.

Common Pitfalls:
Assuming a default constructor will still exist after declaring other constructors; explicitly declare or default it if you need default construction.

Final Answer:
Compiler