Re: copying an object to a char array and back

From:

"peter koch" <peter.koch.larsen@gmail.com>

Newsgroups:

comp.lang.c++

Date:

11 Jul 2006 01:16:47 -0700

Message-ID:

<1152605807.008619.227200@b28g2000cwb.googlegroups.com>

Rahul wrote:

Hi,

I have following two classes
class base{
  int i;
public:
   virtual void fun() { cout<<i<<"Base \n"; }
};

class d: public base{
  int j;
public:
   void fun() { cout<<"Derived \n"; }
};

and the code is doing something like this.
   d d1;
   char c[100];
   bcopy((char *)&d1, c, sizeof(d));
   factory->process(c); // some factory member which accepts a char *

// Inside factory->process ()
   d *dp=reinterpret_cast<d *> (c);
   dp->fun();

Question: Is it ok to copy an object to a char array and cast it back
like this.

No it is not. In practice this can give problems even for very simple
classes that manage pointers to internal storage (std::string could do
so).

Can there be any memory alignment problem (on a single
processor only).

Also that. There is no guarantee that c is aligned at all.

Or any other problem.

Why do yo do so in the first place? Why not simply create a new object
or copy the "normal" way? (d d2(d1) in the code above).

/Peter