C declarations: write a declaration for "A pointer to a function which receives nothing and returns nothing"

Introduction / Context:
This item checks whether you can construct a function pointer type for a procedure that takes no arguments and returns no value. In modern C, an explicit (void) parameter list indicates no parameters; older code sometimes uses empty parentheses, which historically meant an unspecified parameter list. Both styles appear in real code and documentation.

Given Data / Assumptions:

• Pointer to a function is required.
• The function returns nothing (void).
• The function takes no parameters.
• No qualifiers or calling conventions are specified.

Concept / Approach:

The scheme for function pointers is return_type (*identifier)(parameters). We therefore place the pointer declarator around the identifier with parentheses, and supply the parameter list. Using an empty list () is commonly seen; the most explicit modern form is (void) to declare no parameters. Thus, void (*ptr)() is acceptable, and void (*ptr)(void) is even clearer where supported by your coding standard.

Step-by-Step Solution:

Verification / Alternative check:

With typedefs: typedef void proc_t(void); then proc_t *ptr; has the same meaning as void (*ptr)(void). Practical tests, like assigning ptr = &some_function; and invoking (*ptr)(); confirm correct behavior.

Why Other Options Are Wrong:

void *(ptr)*int; — Invalid grammar; mixes pointer declarators and parameters incorrectly.

void *(*ptr)() — Declares a function pointer returning void*, not void.

void *(*ptr)(*) — Not valid C syntax; parameter list cannot be a bare *.

Common Pitfalls:

• Omitting parentheses around *ptr, which changes the declaration's meaning.
• Confusing returning void with returning void*; these are completely different types.

Final Answer:

void (*ptr)()