Re: Copy Constructor

From:

Roy <royashish@gmail.com>

Newsgroups:

comp.lang.c++

Date:

Mon, 30 Jul 2007 03:21:01 -0700

Message-ID:

<1185790861.469145.9040@k79g2000hse.googlegroups.com>

On Jul 30, 2:52 pm, Roy <royash...@gmail.com> wrote:

On Jul 30, 1:18 pm, Dima Stopel <bravo...@gmail.com> wrote:

On Jul 30, 7:24 am, Ian Collins <ian-n...@hotmail.com> wrote:

Roy wrote:

On Jul 30, 9:00 am, Ian Collins <ian-n...@hotmail.com> wrote:

royash...@gmail.com wrote:

   // Destructor
   ~cpchk(){
   cout<<"Destructor called"<<endl;
   if(name!=0)
           free(name);
   }
   a=b;
Heres the code i am talking about , Kindly comment .

Two serious errors:

You attempt to free name twice (why the check for 0?), whether or not it
was allocated by malloc.

--
Ian Collins.

Hi Ian ,

I have checked for 0 , as in the constructor i equate the pointer to
0 , that way my program knows how to check
against freeing a pointer not allocated memory .

Freeing NULL is a no-op, so you don't have to check.

In your case, you have no way of telling whether the name points to
dynamic memory.

I didn't get your point of freeing name twice . There are two
different Objects in the program . Both need to
have their memory freed ?

Once you assign one to the other, both have a name pointer pointing to
the same address. Try printing the pointer value in your destructor.

--
Ian Collins.

I that one of the problems is in the following function:

        // Methods for name
        char* getname()const{
                cout<<"Address:Name>>"<<&name<<endl;
                return name;
        }

You print the pointer to pointer to name and not the actual value of
the pointer.
If you change this line: cout<<"Address:Name>>"<<&name<<endl;
to this line: cout<<"Address:Name>>"<<(void*)name<<endl;
you will get the following output:

Constructor called
Constructor called

Before Assignent
Object A
0012FF50
Address:Name>>00356328
Hitesh
Address:Num>>0012FF54
10
Object B
0012FF40
Address:Name>>00356370
Rajesh
Address:Num>>0012FF44
30

After Assignent
Object A
0012FF50
Address:Name>>00356370
Rajesh
Address:Num>>0012FF54
30
Object B
0012FF40
Address:Name>>00356370
Rajesh
Address:Num>>0012FF44
30
Press any key to continue . . .
Destructor called
Destructor called

After the copy operation the name addresses are the same. This is what
you have expected, not ?

Yes , your observation with the code is correct , Its a fault and
actually printing the pointer to a pointer .
and yes after the copy operation the name addresses are the
same :-) .

Thanks
Dima

continuing with the initialization list this code compiles okay and runs fine but does it create a memory leak ?

class x{
public:
char* getname(){return b}
x():b(NULL){}
x(acName):b(acName){}
~x(){}
private:
char* b;
};
main(){
x *a;
a=new x("ashish");
cout<<a->getname()<<endl;
delete a;
}

Kindly point out the errors in this code ?