Function pointer without arguments types?

Question

I was trying to declare a function pointer that points to any function that returns the same type. I omitted the arguments types in the pointer declaration to see what error

Answer 1

Empty parentheses within a type name means unspecified arguments. Note that this is an obsolescent feature.

C11(ISO/IEC 9899:201x) §6.11.6 Function declarators

The use of function declarators with empty parentheses (not prototype-format parameter type declarators) is an obsolescent feature.