大多数人说永远不要从析构函数抛出异常——这样做会导致未定义的行为。Stroustrup指出,“vector析构函数显式地为每个元素调用析构函数。这意味着如果元素析构函数抛出,则vector销毁失败…实际上没有很好的方法来防止析构函数抛出异常,因此标准库不保证元素析构函数是否抛出”(摘自附录E3.2)。

这篇文章似乎不是这么说的——抛出析构函数或多或少是可以的。

所以我的问题是,如果从析构函数抛出导致未定义的行为,你如何处理析构函数期间发生的错误?

如果在清理操作期间发生错误,您会忽略它吗?如果它是一个可以在堆栈中处理但不能在析构函数中处理的错误,那么从析构函数抛出异常难道没有意义吗?

显然,这种错误很少见,但也有可能发生。


当前回答

我目前遵循的策略(很多人都这么说)是,类不应该主动从析构函数抛出异常,而是应该提供一个公共的“关闭”方法来执行可能失败的操作……

...but I do believe destructors for container-type classes, like a vector, should not mask exceptions thrown from classes they contain. In this case, I actually use a "free/close" method that calls itself recursively. Yes, I said recursively. There's a method to this madness. Exception propagation relies on there being a stack: If a single exception occurs, then both the remaining destructors will still run and the pending exception will propagate once the routine returns, which is great. If multiple exceptions occur, then (depending on the compiler) either that first exception will propagate or the program will terminate, which is okay. If so many exceptions occur that the recursion overflows the stack then something is seriously wrong, and someone's going to find out about it, which is also okay. Personally, I err on the side of errors blowing up rather than being hidden, secret, and insidious.

关键是容器保持中立,由所包含的类决定它们是否从析构函数抛出异常。

其他回答

设置告警事件。通常,警报事件是在清理对象时通知失败的更好形式

作为对主要答案的补充,这些答案是好的,全面的和准确的,我想评论一下你引用的文章——那篇文章说“在析构函数中抛出异常并不是那么糟糕”。

本文以“抛出异常的替代方法是什么”为题,并列举了每种替代方法的一些问题。这样做后,它得出结论,因为我们找不到一个没有问题的替代方案,所以我们应该继续抛出异常。

问题在于,它列出的所有问题都没有异常行为那么糟糕,让我们记住,异常行为是“程序的未定义行为”。作者的一些反对意见包括“美学上的丑陋”和“鼓励糟糕的风格”。现在你想要哪一个?一个风格糟糕的程序,还是一个表现出未定义行为的程序?

Martin Ba(上图)在正确的轨道上——你为RELEASE和COMMIT逻辑构建了不同的架构。

发布:

你应该吃任何错误。您正在释放内存、关闭连接等。系统中的任何人都不应该再看到这些东西,并且您正在将资源交还给操作系统。如果你看起来需要真正的错误处理,这可能是你的对象模型设计缺陷的结果。

提交:

This is where you want the same kind of RAII wrapper objects that things like std::lock_guard are providing for mutexes. With those you don't put the commit logic in the dtor AT ALL. You have a dedicated API for it, then wrapper objects that will RAII commit it in THEIR dtors and handle the errors there. Remember, you can CATCH exceptions in a destructor just fine; its issuing them that's deadly. This also lets you implement policy and different error handling just by building a different wrapper (e.g. std::unique_lock vs. std::lock_guard), and ensures you won't forget to call the commit logic- which is the only half-way decent justification for putting it in a dtor in the 1st place.

其他人都解释了为什么抛出析构函数很糟糕……你能做些什么呢?如果您正在执行一个可能失败的操作,请创建一个单独的公共方法来执行清理,并可以抛出任意异常。在大多数情况下,用户会忽略这一点。如果用户希望监视清理的成功/失败,他们可以简单地调用显式清理例程。

例如:

class TempFile {
public:
    TempFile(); // throws if the file couldn't be created
    ~TempFile() throw(); // does nothing if close() was already called; never throws
    void close(); // throws if the file couldn't be deleted (e.g. file is open by another process)
    // the rest of the class omitted...
};

我所在的小组认为,在析构函数中加入“作用域保护”模式在许多情况下都很有用——特别是对于单元测试。但是,要注意,在c++ 11中,抛出析构函数会导致调用std::terminate,因为析构函数隐式地用noexcept注释。

Andrzej krzemiezynski有一篇关于抛出析构函数的文章:

https://akrzemi1.wordpress.com/2011/09/21/destructors-that-throw/

他指出c++ 11有一种机制可以覆盖析构函数的默认noexcept:

In C++11, a destructor is implicitly specified as noexcept. Even if you add no specification and define your destructor like this: class MyType { public: ~MyType() { throw Exception(); } // ... }; The compiler will still invisibly add specification noexcept to your destructor. And this means that the moment your destructor throws an exception, std::terminate will be called, even if there was no double-exception situation. If you are really determined to allow your destructors to throw, you will have to specify this explicitly; you have three options: Explicitly specify your destructor as noexcept(false), Inherit your class from another one that already specifies its destructor as noexcept(false). Put a non-static data member in your class that already specifies its destructor as noexcept(false).

最后,如果您决定抛出析构函数,则应该始终注意双异常的风险(在堆栈因异常而被unwind时抛出)。这将导致调用std::terminate,这很少是您想要的。为了避免这种行为,你可以使用std::uncaught_exception()在抛出一个新的异常之前检查是否已经有一个异常。