你可以通过转换操作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

我不知道如何在短主题行中很好地说出问题，所以让我尝试更长的解释。假设我有这些异常类：

  class ExceptionTypeA：public std :: runtime_error 
 {
 // stuff 
}; 
 
 class ExceptionTypeB：public std :: runtime_error 
 {
 // stuff 
 
操作符ExceptionTypeA（）const; // conversion operator to ExceptionTypeA 
};我可以这样做，并且它触发catch块吗？
 
 
 
 
 
 
 $ b < b 
 
  try 
 {
 throw ExceptionTypeB（）; 
} 
 catch（ExceptionTypeA& a）
 {
 //会被触发吗？ 
} 
  
 
 
我会猜测不会，这是不幸的，但我想我会问，因为我在网上或在SO上找不到任何信息。是的，我意识到我可以在我的编译器运行程序，看看会发生什么，但不会告诉我什么标准说这个行为，只是我的编译器实现（我不相信它）。
解决方案
你不能。标准版 15.3 / 3 ：
 
 
处理程序与异常对象如果
 
 
 
 
 
处理程序类型为 cv T 或 cv T& 和E和T是相同的类型（忽略顶级cv- 
限定符），或
 
 
是 cv T 或 cv T& 类型，T是E的明确公共基类，或
 
 
处理程序类型为 cv1 T * cv2 ，E是可以转换为处理程序类型的指针类型
 
 
 
 
一个标准指针转换（4.10），不涉及转换为private或protected或
模糊类的指针
 
 
资格转换
 
 
 
 
 
 
 
期望场景与这些都不匹配。  cv 表示const和/或易失性组合
 
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
};
Can I then do this, and have it trigger the catch block?
try
{
    throw ExceptionTypeB();
}
catch (ExceptionTypeA& a)
{
    // will this be triggered?
}
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).
解决方案
You cannot. Standardese at 15.3/3:

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

                        
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