异常多重继承 [英] Exception multiple inheritance

问题描述

我在混合异常和多重继承时遇到问题.基本上我有以下代码:

I have the problem with mixing exceptions and multiple inheritance. Basically I have this code:

#include <exception>
#include <stdexcept>
#include <iostream>

class A : public std::exception
{
public:
    virtual ~A() noexcept {};
};

class B : public A, public std::runtime_error
{
public:
    B() : A{}, std::runtime_error{""}
    {

    }
};

int main()
{
    try {
        throw B{};
    } catch (const std::exception& error) {
        // this catch doesn't work
        std::clog << "Caught!" << std::endl;
    }
}

我需要修改它，以便可以将类B的异常捕获为std :: exception(现在调用了终止处理程序).我如何实现这种行为?我想需要虚拟继承，但是在这种情况下我看不到任何使用它的方法.

What I need is to modify it so that exception of class B can be caught as std::exception (for now the terminate handler is called). How can I achieve such behavior? I guess virtual inheritance is needed but I don't see any way to use it in this case.

更新:我需要能够:
-将A视为A(琐碎)，
-将A捕获为std :: exception，
-将B捕获为B(再次，琐碎)，
-将B捕获为std :: exception，
-将B捕获为std :: runtime_error

UPDATE: I need to be able to:
- catch A as A (trivial),
- catch A as std::exception,
- catch B as B (again, trivial),
- catch B as std::exception,
- catch B as std::runtime_error

我知道这是很多要求，也许没有多大意义，但是我需要它，我很好奇:)

I know this is a lot of requirements, and maybe it doesn't make much sense, but I need it and I'm just curious:)

UPDATE2:我认为问题是std :: runtime_error实际上不是从std :: exception派生的(这将允许我通过A中的虚拟继承来解决问题).我对吗?仍然可以解决吗?

UPDATE2: I think the problem is std::runtime_error not derving virtually from std::exception (which would allow me to solve problem by by virtual inheritance in A). Am I right? Still, can it be solved?

UPDATE3:艾伦·斯托克斯(Alan Stokes)在下面的评论中建议了解决方案，这似乎对我有用:

UPDATE3: Alan Stokes suggested solution in comments below, which seems to work for me:

是否可以将A分为两类-一类实现B所需的功能，另一类增加对std :: exception的继承?这样，A和B都可以从(例如)A_base继承.

Can you split A into two classes - one that implements the functionality B needs, and one that adds in the inheritance from std::exception? Then both A and B could inherit from (say) A_base.

感谢您，但是如果有人还有其他好的解决方案，请告诉我.

Thanks for that, still if anyone has other good solutions please let me know.

推荐答案

Stroustrup建议以虚拟方式从std::exception继承，以便只有一条转换路径.

Stroustrup recommends to inherit from std::exception virtually, so that there is only one conversion path.

我个人认为，制定多重继承方案可能是过度工程，并且更喜欢线性继承链...或者根本没有.

Personally, I find that working out a multiple inheritance scheme is probably over-engineering and prefer a linear inheritance chain... or just none at all.

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