Re: copy construct

From:

Jens Schmidt <Jens.Schmidt-HH@gmx.de>

Newsgroups:

comp.lang.c++.moderated

Date:

Sun, 9 Aug 2009 07:51:16 CST

Message-ID:

<7e67ivF2f2rbhU1@mid.uni-berlin.de>

exergy wrote:

Hello, if I have a class like this:

  class Node{
    private:
       int x;
       Node* parent;
    public:
        Node(const Node& N)
          {
                ......
          }
         Node& operator =(const Node& n)
        {
                 ......
         }

       ~Node()
        {
              .....
        }
         // other member functions
  }

How do I make a copy of private field Node* parent itself? I read some
references online, some use "new" operator to allocate dynamic memory,
so what I did was

    Node(const Node& p)
      {
        x=p.x;
        Node temp=*(p.parent)
        parent=new node(temp);
      }
However, x value was copied, not the parent pointer.
anyone can help?

You first have to decide if you want a shallow copy or a deep copy of your
Node. For a shallow copy, a simple assignment of parent=p.parent is
sufficient. For a deep copy, your code has to be modified so that all
parents are copied, but not more. Currently, you ignore that the parent
field may be NULL. Code like

      Node(const Node& p)
        {
          x=p.x;
          if (p.parent)
            parent=new Node(*(p.parent));
          else
            parent=0;
        }

will do this by using recursion, but can be improved for this linear list
by changing this to iteration.
--
Greetings,
   Jens Schmidt

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