C ++：在非特殊情况下是否有理由使用异常 [英] C++: Are there reasons to use exceptions in non exceptional situations

问题描述

让我给你下面的例子：假设你有一个窗口类，可以有子窗口。每个子窗口都有一个指向其父窗口的弱指针，每个窗口都有一个共享ptrs列表给它的子窗口。现在我有这样的情况，如果子窗口被破坏，我不知道它是否被破坏，因为父窗口被关闭，或者因为子窗口本身被关闭。因此，我想出的解决方案是在try {} catch {}块中的子窗口析构函数中取消引用父窗口弱指针，以查看父窗口是否仍然存在（伪代码）：

  //我们尝试在这里保留父窗口
 try 
 {
 //从弱指针创建一个共享指针， throws BadReferenceCounterException on fail 
 WindowPtr parent = m_parentWindow.retain（）; 
 
 //检查是否有父节点，否则为0 
 if（parent）
 {
 parent-> removeChildWindow（this）; 
} 
} 
 catch（const BadReferenceCounterException& _ec）
 {
 std :: cout<<如果父母在我之前关闭， << std :: endl; 
} 
  

在这种情况下，我不能想到另一种解决方法，没有办法知道析构函数被调用的上下文。这是一个愚蠢的事情，因为我在一种预期的情况下使用异常？我知道这不是你想在性能关键代码中做的事情，所以这不是问题的问题。

谢谢！

解决方案

您似乎使用错误的共享/弱指针对。标准（在C ++ 11和boost中）共享/弱指针允许你没有异常：

  typedef std :: shared_ptr< Window> WindowPtr; 
 typedef std :: weak_ptr< Window> WeakWindowPtr; 
 
 WeakWindowPtr m_parentWindow; 
 // ... 
 
 WindowPtr parent = m_parentWindow.lock（）; 
 if（parent）
 {
 //这里你知道父代没有被销毁，你可以通过父代
} 
  
 
 
 
您还可以查看我在 this stackoverflow answer  
 
Let me give you the following example: Imagine you have a window class which can have child windows. Each child window holds a weak pointer to its parent window, each window has a list of shared ptrs to its children. Now i have the situation that if the child window is destructed, I can't know if it is destructed because the parent window was closed, or because the child window itself was closed. Therefore the solution I came up with was to dereference the parent windows weak pointer in the child windows destructor in a try{}catch{} block to see if the parent window still exists (pseudocode):
 //we try to retain the parent window here
 try
 {
     //creates a shared pointer from the weak pointer, throws BadReferenceCounterException on fail
     WindowPtr parent = m_parentWindow.retain();

     //check if there is a parent at all, otherwise 0
     if(parent)
     {
         parent->removeChildWindow(this);
     }
  }
  catch(const BadReferenceCounterException & _ec)
  {
     std::cout<<"Catched expected exception, if Parent was closed before me!"<<std::endl;
  }
In this situation I could not think of another way to solve this simply because there is no way to know the context in which the destructor was called. Is this a stupid thing to do because I use an exception in a sort of expected situation? I know this is not a thing you want to do in performance critical code so this is not the point of the question.

Thank you!
解决方案
You seem to be using faulty shared/weak pointer pair. Standard (both in C++11 and in boost) shared/weak pointers allow you to do it without exceptions:
typedef std::shared_ptr<Window> WindowPtr;
typedef std::weak_ptr<Window> WeakWindowPtr;

WeakWindowPtr m_parentWindow;
//...

WindowPtr parent = m_parentWindow.lock();
if (parent)
{
  // here you know parent wasn't destroyed and you can access it via parent
}
You may also want to check out code samples I've given in this stackoverflow answer

                        
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