Re: Copy C'tor - doubt

From:
"Martin B." <0xCDCDCDCD@gmx.at>
Newsgroups:
comp.lang.c++.moderated
Date:
Fri, 20 Nov 2009 04:01:52 CST
Message-ID:
<he5lam$5v8$1@news.eternal-september.org>
AY wrote:

I have a situation where I'm required to generate a copy of an object.
I have simplified the class into a tiny one, but in reality its a huge
class with multiple struct types as data member.

Here is my simplified class:

class AB
{
         private:
                 int a;
         public:

         AB(int ar): a(ar){}

         AB(const AB& arg)
         {
                 a = arg.a;
         }
};


Better make this:
AB(const AB& arg)
: a(arg.a)
{ }

Also: if you define a copy-ctor you also want to define a copy operator.
(Or as in this case - just go with the copiler generated ones.)

int main()
{
         AB* ab = new AB(7);

         //AB* cd = new AB;

         AB* cd(ab);

         return 0;
}

My Qn is in the statement - AB* cd(ab);

Does object 'cd' uses the same memory as object 'ab' ?

Is any memory allocated in the heap for 'cd' like 'ab' [ I do not
think, maybe I'm wrong ] ?


cd and ab are POINTERS to a an object constructed in free-store (heap)
and as such both point to exactly the same AB entitiy. Initializing /
assigning a pointer doesn't invoke anything.

AB* p = ab; // or p(ab); // pointer init: p and ab point to the same thing
AB obj(*ab); // or maybe obj = *ab; // invokation of copy-ctor and
creation of a new object (on the stack)

br,
Martin

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