C++中异常的栈展开概念

C++中的异常栈展开是指，当某个函数中有异常产生（这里不考虑是主动抛出的还是被动产生的），在异常被捕获之前的函数调用链上，函数不会正常执行返回，即异常产生之后的程序逻辑不会被执行。
（注意：这里不从操作系统层面来讨论函数调用栈等相关观念）

看下面一个示例：C++ 中的异常和堆栈展开

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

class MyException{};
class Dummy
{
    public:
    Dummy(string s) : MyName(s) { PrintMsg("Created Dummy:"); }
    Dummy(const Dummy& other) : MyName(other.MyName){ PrintMsg("Copy created Dummy:"); }
    ~Dummy(){ PrintMsg("Destroyed Dummy:"); }
    void PrintMsg(string s) { cout << s  << MyName <<  endl; }
    string MyName;
    int level;
};

void C(Dummy d, int i)
{
    cout << "Entering FunctionC" << endl;
    d.MyName = " C";
    throw MyException();

    cout << "Exiting FunctionC" << endl;
}

void B(Dummy d, int i)
{
    cout << "Entering FunctionB" << endl;
    d.MyName = "B";
    C(d, i + 1);
    cout << "Exiting FunctionB" << endl;
}

void A(Dummy d, int i)
{
    cout << "Entering FunctionA" << endl;
    d.MyName = " A" ;
    B(d, i + 1);
    cout << "Exiting FunctionA" << endl;
}

int main()
{
    cout << "Entering main" << endl;
    try
    {
        Dummy d(" M");
        A(d,1);
    }
    catch (MyException& e)
    {
        cout << "Caught an exception of type: " << typeid(e).name() << endl;
    }

    cout << "Exiting main." << endl;
}

/* Output:
    Entering main
    Created Dummy: M
    Copy created Dummy: M
    Entering FunctionA
    Copy created Dummy: A
    Entering FunctionB
    Copy created Dummy: B
    Entering FunctionC
    Destroyed Dummy: C
    Destroyed Dummy: B
    Destroyed Dummy: A
    Destroyed Dummy: M
    Caught an exception of type: class MyException
    Exiting main.
*/