c++ - 如果通过引用捕获异常，是否可以修改并重新抛出？

Question

该标准是否对通过引用捕获的异常以及修改它的尝试有什么要说明？

考虑以下代码:

class my_exception: public std::logic_error
{
public:
    std::vector<std::string> callstack;
};

void MyFunc()
{
    try
    {
        SomethingThatThrows();
    }
    catch (my_exception & e)
    {
        e.callstack.push_back("MyFunc");
        throw;
    }
}

这是一个人为的例子，我实际上并没有尝试这样的事情。我只是好奇会发生什么，基于另一个线程中的建议，异常应该由 const 引用捕获。

Answer 1

异常会改变。

§15.3[except.handle]/17:

When the handler declares a non-constant object, any changes to that object will not affect the temporary object that was initialized by execution of the throw-expression.

When the handler declares a reference to a non-constant object, any changes to the referenced object are changes to the temporary object initialized when the throw-expression was executed and will have effect should that object be rethrown.

因此，如果 my_exception 在 MyFunc 之外被捕获，我们将在调用堆栈中看到 "MyFunc" 条目(例如 http://ideone.com/5ytqN )