c++ - 从 std::runtime_error 私有(private)继承的类未被捕获为 std::exception

Question

都在这个例子里

class MyException: std::runtime_error // note, there is no public keyword in inheritance
{
public:
   MyException(const std::string & x)
      : std::runtime_error(x)
   {}
};


int main( )
{
   try
   {
      throw MyException("foo");
   }
   catch (std::exception & e )
   {
      std::cout << "catched std exception: " << e.what() << std::endl;
   }
   catch (...)
   {
      std::cout << "catched ... " << std::endl;
   }
}

它在标准输出字符串“catched ...”上写入。但是，如果我将继承更改为 public 作为 class MyException : public std::runtime_error，它会按预期工作(对我而言)并写入“catched std exception: foo”

c++ 标准的哪一部分要求这样的行为？为什么？在什么情况下这种行为可能有用？

Answer 1

有道理，符合重载决议的规则。在 MyException 之外，您的类不是 std::exception。您应该将私有(private)继承视为一个实现细节(具有非常高的耦合度。)

在15.3处理异常中:

A handler is a match for an exception object of type E if

— The handler is of type cv T or cv T& and E and T are the same type (ignoring the top-level cv-qualifiers), or

— the handler is of type cv T or cv T& and T is an unambiguous public base class of E, or

— the handler is of type cv1 T* cv2 and E is a pointer type that can be converted to the type of the handler by either or both of - a standard pointer conversion (4.10) not involving conversions to pointers to private or protected or ambiguous classes — a qualification conversion

— the handler is a pointer or pointer to member type and E is std::nullptr_t.

(强调我的)