You said:
Please provide me with a guide / specification that states that it is prohibited. I want to be sure that this is really required by the language or just a compiler error.
WITH
void (**fp)() throw() ;
You are trying to specify an exception specification in a pointer declaration to a function pointer. This is prohibited by standard. Exclusion specifications are allowed only for a limited set of ads.
From https://timsong-cpp.imtqy.com/cppwp/n3337/except.spec#2 (my attention):
An exception specification should only appear in a function declaration for a function type , a pointer to a function type , a reference to a function type , or a pointer to a member function type that is a top-level declaration type or definition, or that type that appears as a parameter or return type values in function declaration . An exception specification should not appear in a typedef declaration or alias declaration. [Example:
void f() throw(int); // OK void (*fp)() throw (int); // OK void g(void pfa() throw(int)); // OK typedef int (*pf)() throw(int); // ill-formed
- end of example] The type indicated in the exception specification should not indicate an incomplete type. The type indicated in the exception specification must not indicate a pointer or reference to an incomplete type except void* , const void* , volatile void* or const volatile void* . Type cv T , "array of T " or "function return T " indicated in the exception specification is configured to type T , "pointer to T " or "pointer to function returning T ", respectively.
You asked:
If it is from the language specification, what motivates this rule?
I have no answer to this question.