您可以通过转换运算符的类型捕获异常吗？ [英] Can you catch an exception by the type of a conversion operator?

问题描述

我不知道如何在一个简短的主题行中很好地说出这个问题，所以让我尝试一个更长的解释。假设我有这些异常类：

I don't know how to phrase the question very well in a short subject line, so let me try a longer explanation. Suppose I have these exception classes:

class ExceptionTypeA : public std::runtime_error
{
    // stuff
};

class ExceptionTypeB : public std::runtime_error
{
    // stuff

    operator ExceptionTypeA() const; // conversion operator to ExceptionTypeA
};

然后我可以这样做，并触发catch块吗？

Can I then do this, and have it trigger the catch block?

try
{
    throw ExceptionTypeB();
}
catch (ExceptionTypeA& a)
{
    // will this be triggered?
}

我要猜测它不会，这是不幸的，但是我以为我会问，因为我没有在网上或在SO上找到任何信息。是的，我意识到我可以在我的编译器中运行程序，看看会发生什么，但是不能告诉我这个行为的标准是什么，就是我的编译器实现的（我不相信它） / p>

I'm going to guess that it will not, which is unfortunate, but I thought I'd ask, since I couldn't find any info on it on the net or on SO. And yes, I realize I could just run the program in my compiler and see what happens, but that wouldn't tell me what the standard says about this behavior, just what my compiler implements (and I don't trust it).

推荐答案

你不能。标准在 15.3 / 3 ：

处理程序是一个异常对象的匹配如果

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

• 处理程序的类型为$ code> cv T 或 cv T& 和E和T是相同的类型（忽略顶级cv-
  限定词），或者


• 处理程序是 cv T 或 cv T& ，T是E的明确的公共基类，或


• 处理程序的类型为 cv1 T * cv2 ，E是可以转换为处理程序类型的指针类型
  通过
  
  
  
  
  • 不涉及到私有或受保护的指针的转换的标准指针转换（4.10）或
    模糊类
  
  
  • 资格转换
  
  
  • 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

    您所需的场景不符合这些情况。 cv 表示const和/或volatile组合

    Your desired scenario matches none of these. cv means "const and/or volatile combination"

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