c++ - Constructor finishes by throwing an exception ? Is there a memory leak?

Question

I was going over this article and it states

Note: if a constructor finishes by throwing an exception, the memory associated with the object itself is cleaned up — there is no memory leak. For example:

void f()
{
X x; // If X::X() throws, the memory for x itself will not leak
Y* p = new Y(); // If Y::Y() throws, the memory for *p itself will not leak
}

I am having difficulty understanding this and would appreciate it if someone could clarify this. I tried the following example which shows that incase of an exception inside a constructor the destructor would not be called.

struct someObject
{
    someObject()
    {
      f = new foo();    
      throw 12;
    }
    ~someObject()
    {
        std::cout << "Destructor of someobject called";
    }

    foo* f;
};

class foo
{
public:
    foo()
    {
            g = new glue();
            someObject a;
    }
    ~foo()
    {
        std::cout << "Destructor of foo";
    }
 private:
  glue* g;
};


int main()
{
    try
    {
        foo a;
    }
    catch(int a)
    {
        //Exception caught. foo destructor not called and someobject destrucotr not called.
       //Memory leak of glue and foo objects
    }
}

How would I fix this issue ?

Sorry for the inconvenience the update might have caused.

Answer 1

When the constructor throws, no destructor will be called. When an exception is thrown inside a constructor there are several things that you should take note of in terms of properly handling resource allocations that may have occured in the aborted construction of the object:

• the destructor for the object being constructed will not be called.
• destructors for member objects contained in that object's class will be called
• the memory for the object that was being constructed will be freed.