类的构造函数中异常处理的行为

我有这个程序，派生类的ctor抛出异常。该程序只是一个示例程序，我只是想了解异常处理的概念。类的构造函数中异常处理的行为

class A{ 
public: 
    A() {} 

    ~A(){std::cout << "DTOR called - A!!" << std::endl;} 
}; 

class B : public A 
{ 
public: 
    B():A() 
    { 
     try 
     { 
     init(); 
     } 
     catch(...) 
     { 
     std::cout << "Inside catch block in B's Ctor!!" << std::endl; 
     throw this; 
     } 
    } 

    void init() { throw 0; } 

    ~B() {std::cout << "DTOR called - B!!" << std::endl; } 
}; 

int main() 
{ 
    try{ 
     B *b = new B; 

     std::cout << "Äfter B's ctor called in try block!!" << std::endl; 
     delete b; 
     std::cout << "Äfter B's dtor called in try block!!" << std::endl; 
    } 

    catch(B* b) 
    { 
     delete b; 
     b = NULL; 
     std::cout << "Exception Occurred in B!!" << std::endl; 
    } 

    catch(A* a) 
    { 
     delete a; 
     a = NULL; 
     std::cout << "Exception Occurred in A!!" << std::endl; 
    } 

    catch(...) 
    { 
     std::cout << "Exception Occured!!" << std::endl; 
    } 
    return EXIT_SUCCESS; 
}

预期的输出是它应该进入B的catch块，并且应该调用第一个B的dtor，然后调用A的dtor。但上述程序的输出是：

Inside catch block in B's Ctor!! 
DTOR called - A!! 
DTOR called - B!! 
DTOR called - A!! 
Exception Occurred in B!!

我想问这是为什么A类的析构函数调用了两次，当它只是引入了B类的catch块，并呼吁只有B类的析构函数？也请告诉我是否在这里犯了一些错误。任何帮助表示赞赏

编辑：

class B : public A 
{ 
public: 
    B():A() 
    { 
     try 
     { 
     szName = new char[100]; 
     init(); 
     } 
     catch(...) 
     { 
     std::cout << "Inside catch block in B's Ctor!!" << std::endl; 
     throw this; 
     } 
    } 

    void init() { throw 0; } 

    ~B() 
    { 
     delete szName; 
     std::cout << "DTOR called - B!!" << std::endl; 
    } 

    char *szName; 
};

在这里，我在构造函数try块创建了一个字符指针类B.分配的内存被抛出异常之前。现在在这种情况下，如果我没有发现类B的异常，会不会有内存泄漏？

来源

2014-10-07 Saurabh Bhola

见http://www.gotw.ca/gotw/066.htm – 2014-10-07 06:33:29