C++ default arguments: which statement below is incorrect regarding default function arguments?

Introduction / Context:
Default arguments in C++ let callers omit trailing parameters. They are inserted by the compiler at the call site. Understanding where defaults are allowed and the one-definition rules prevents ambiguous interfaces and linker surprises—especially in multi-declaration scenarios and for function-pointer parameters.

Given Data / Assumptions:

• We consider regular functions and parameters that may be function pointers.
• We allow all parameters to have defaults if desired.
• We respect the rule: provide defaults once (typically in a header), not repeatedly.

Concept / Approach:

Default arguments may be supplied for any parameter, including a pointer-to-function parameter: e.g., void f(int, int (*pf)() = nullptr);. An entire parameter list may be defaulted, making the function callable with no arguments. However, a default argument must be specified only once for a given parameter across declarations; redeclaring a different default later is ill-formed. Therefore, the incorrect statement is the claim that “Default argument cannot be provided for pointers to functions.” It can be provided.

Step-by-Step Solution:

Verification / Alternative check:

Compile a sample where a function-pointer parameter has a default. It compiles. Add a second declaration that attempts to change the default and observe a compile-time error, confirming D and refuting C.

Why Other Options Are Wrong:

Labelled “wrong” here means “not the incorrect statement.” A, B, and D are all accurate rules of C++ defaults.

Common Pitfalls:

• Placing defaults in multiple headers or both declaration and definition.
• Forgetting that callers must omit only a suffix of arguments; you cannot skip a middle parameter.

Final Answer:

Default argument cannot be provided for pointers to functions.