异常处理中的混乱

Question

考虑以下程序

#include <iostream>
#include<cstdlib>
using namespace std;

class E {
   public:
      const char* error;
      E(const char* arg) : error(arg) { }
};

void my_terminate() {
  cout << "Call to my_terminate" << endl;
}

struct A {
  A() { cout << "In constructor of A" << endl; }
  ~A(){
    cout << "In destructor of A" << endl;
    throw E("Exception thrown in ~A()");
  }
};

struct B {
  B() { cout << "In constructor of B" << endl; }
  ~B() { cout << "In destructor of B" << endl; }
};

int main() {

  set_terminate(my_terminate);

  try {
    cout << "In try block" << endl;
    A a;
    B b;
    throw E("Exception thrown in try block of main()"); // Line 36
  }
  catch (E& e) {
    cout << "Exception: " << e.error << endl;
  }
  catch (...) {
    cout << "Some exception caught in main()" << endl;
  }

  cout << "Resume execution of main()" << endl;

}

输出:

In try block
In constructor of A
In constructor of B
In destructor of B
In destructor of A
Call to my_terminate

Disallowed system call: SYS_kill

在第36行中,从main中的try块抛出异常.现在为什么这个异常没有被处理程序捕获？

相反,'堆栈展开'过程继续.A的析构函数也抛出一个异常,它再次没有被任何处理程序捕获,而是调用my_terminate了,为什么？

为什么在这两种情况下不调用处理程序？

Answer 1

C++规则是,您必须永远不要从另一个异常的"堆栈展开"过程中调用的析构函数中抛出异常.

你在A析构函数中抛出异常,这是你不应该做的事情.