C++，函数指针异常错误

Question

我使用以下代码得到 "error: exception specifications are not allowed beyond a single level of indirection"。请指出标准中不允许的部分。我想确定它确实是语言所必需的，或者只是编译器特定的错误。如果它来自语言规范，那么这条规则的动机是什么？我正在使用 clang 3.8.0.

  int main()
    {
        void (**fp)() throw() ;
    }

Answer 1

你说：

Please point me to a reference book /spec that says that it is not allowed. I want to be sure that it is really required by the language or just compiler specific error.

与

void (**fp)() throw() ;

您正试图在指向函数指针的指针声明中指定异常规范。这是标准不允许的。 异常规范 仅允许用于一组有限的声明。

来自 https://timsong-cpp.github.io/cppwp/n3337/except.spec#2（强调我的）：

An exception-specification shall appear only on a function declarator for a function type, pointer to function type, reference to function type, or pointer to member function type that is the top-level type of a declaration or definition, or on such a type appearing as a parameter or return type in a function declarator. An exception-specification shall 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 example ] A type denoted in an exception-specification shall not denote an incomplete type. A type denoted in an exception-specification shall not denote a pointer or reference to an incomplete type, other than void*, const void*, volatile void*, or const volatile void*. A type cv T, “array of T”, or “function returning T” denoted in an exception-specification is adjusted to type T, “pointer to T”, or “pointer to function returning T”, respectively.

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你问过：

If it is from language specification, what motivates this rule?

我没有答案。