析构函数C ++中的异常 [英] Exception in Destructor C++

问题描述

我很清楚一个事实，即不应在析构函数中抛出任何异常。

I am well aware of the fact that one should not throw any exception in destructor.

但是，为了牢牢抓住这个概念，我编写了这个代码例如：-

But as a part of making my grip on this concept,I coded this example :-

#include <iostream>
using namespace std;

class A {
private: 
    int i;

public:
    A()
    {
        i = 10;
    }
    ~A()
    {
        throw 30;
    }
};
int main(){
    try{
        A();
        throw 10;
    }
    catch (int i){
        cout << i << endl;
        cout << "exception caught" << endl;
    }
}

根据我的理解，该程序应以调用std :: terminate（），因为同时会有两个异常。但是，该程序给出以下输出：-

As per my understanding, this program should be terminated by calling std::terminate() as there will be two exceptions at the same time. But, this program is giving the following output:-

30
exception caught

有人可以向我解释为什么这没有终止的逻辑吗？

Can anyone please explain me the logic behind this as to why this is not terminating?

推荐答案

std :: terminate 将在堆栈退卷期间引发异常时调用。这意味着如果在处理另一个异常的同时调用一个异常，则将调用 std :: terminate 。

std::terminate will be called if an exception is thrown during stack unwinding. That means that if an exception is called while another exception is being handled, then std::terminate will be called.

在您的示例中，这不会发生- A（）; 将构造并立即销毁一个实例 A 。然后会正确捕获抛出30 。

In your example, that doesn't happen - A(); will construct and immediately destroy an instance of A. The throw 30 will then be caught correctly.

将代码更改为：

int main(){
    try{
        A a;      // begin `a` lifetime 
        throw 10; // | throw #0           
                  // | end `a` lifetime   
                  // throw #1
    }
    catch(int i){
        cout<<i<<endl;
        cout<<"exception caught"<<endl;
    }
}

将保证 std： ：terminate 将被调用。在这种情况下， a 将被销毁并在处理另一个异常时抛出。

will guarantee that std::terminate will be called. In this case, a will be destroyed and will throw while another exception is being handled.

实时大肠杆菌示例

其他信息：

• cppreference / Destructors / Exceptions

StackOverflow：将异常抛出析构函数

请注意，在C ++ 11及更高版本中， ，您的代码段将调用 std :: terminate 并向您提供警告：

Note that in C++11 and above, your code snippet will call std::terminate and provide you a warning:

main.cpp：在析构函数'A ::〜A（）'：

main.cpp: In destructor ‘A::~A()’:

main.cpp：16：15：警告：throw将始终调用Terminate（）
[- Wterminate]

main.cpp:16:15: warning: throw will always call terminate() [-Wterminate]

     throw 30;

           ^~

main.cpp：16：15：注意：<在C ++ 11析构函数中，strong>默认为noexcept

main.cpp:16:15: note: in C++11 destructors default to noexcept

在抛出'int'实例后调用终止

terminate called after throwing an instance of 'int'

bash：第7行：1505中止（核心转储）./a.out

bash: line 7: 1505 Aborted (core dumped) ./a.out

如编译器输出所示，因为C ++ 11 析构函数隐式地 noexcept（true） 。如果要防止此行为，只需将它们标记为 noexcept（false）。示例：

As seen in the compiler output, since C++11 destructors are implicitly noexcept(true). If you want to prevent this behavior, you can simply mark them as noexcept(false). Example:

~A() noexcept(false)
{
    throw 30;
}

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