In C++ function declarations and definitions, what is the correct return type keyword used when a function is intended to return no value at all to its caller?

Introduction / Context:
In C++ programming, every function has a declared return type that informs both the compiler and the caller what kind of result (if any) will be produced when the function completes. Many functions perform actions such as logging, printing, mutating objects via references, or orchestrating control flow without producing a value for the caller. For these cases, the language provides a dedicated keyword to indicate the complete absence of a return value.

Given Data / Assumptions:

• The question asks for the correct C++ return type used when a function should not return a value.
• Standard C++ syntax and semantics are assumed (no compiler-specific extensions).
• We are not discussing templates, coroutines, or special member functions beyond how they relate to the idea of “no return value.”

Concept / Approach:
In C++, the keyword used to denote that a function returns no value is void. A function declared as void f(parameters) signals that control returns to the caller without any accompanying data. Such a function may use an empty return; to exit early, but it cannot return an expression. This is distinct from functions that return a type like int or std::string, where a value must be produced on all control paths. The term “void” is part of the core language and has precise, standardized meaning; alternatives such as “empty” or “barren” are not C++ keywords.

Step-by-Step Solution:

Verification / Alternative check:

• If a function is declared with a non-void return type but does not return a value on all paths, the compiler will typically issue an error or warning. This confirms that “no value” functions must be explicitly marked with void.
• Conversely, attempting to write return 42; inside a void function will produce a compile-time error, verifying that void truly indicates no return value.

Why Other Options Are Wrong:

• not allowed in C++: Incorrect. Functions that return no value are fully supported via the void return type.
• type empty: Not a C++ keyword or type; has no meaning to the compiler.
• type barren: Also not a C++ keyword or recognized type.

Common Pitfalls:

• Confusing a void function with one returning an “empty” object (e.g., an empty std::string). A void function returns nothing at all, not an “empty” value.
• Forgetting that constructors and destructors have no return type specified—this is a special rule; they are not written with void and still return no value.
• Using return expression; inside a void function, which is ill-formed.

Final Answer:
type void.