RE: [Dev-C++] Constructor and Destructor

[Verma, L. <Loh...@hp...>]

Hi,
I take your point regarding not using delete this in constructor.

Now you had said that as the function in a class does not access / update
any data member it works.
In the following program I have specifically set the value of a data
member,this still works.

#include <iostream>
using namespace std;

class A{
        int i;
        public:
        A(){
                cout<<"A const\n";
        }
        void f(){
                cout<<"F\n";
                i=9;
                cout<<"FUNC I "<<i<<endl;
        }
        void g(){
                cout<<"G I "<<i<<endl;
        }
        ~A(){
                cout<<"DEST\n";
        }
};
int main(){
        A *b;
        b->f();
        return 1;
}

OUTPUT
F
FUNC I 9
G I 9

This doesnt make sense to me!!!
I have tried it on both windows and solaris.

Any ideas??
Regards
Lohit

-----Original Message-----
From: Per Westermark [mailto:pw...@ia...]
Sent: Wednesday, July 09, 2003 7:18 PM
To: avi...@ne...
Cc: Verma, Lohit; ''
Subject: Re: [Dev-C++] Constructor and Destructor


Nothing strange here... c->f() only works because:

1: A::f is not virtual, i.e. there is no need to lookup a function pointer
indirectly through the object. It is just a normal function call.

2: A::f() does not try to reference any dynamic data owned by the object.
In this case it calls a globally declared stream with a constant text
string. If it had tried to call a virtual method, or update any member
variables of the A class, it would have failed.

/Per W

On Wed, 9 Jul 2003, Avik Ghose wrote:

>
> Hi Lohit,
>
> look for my answers inline pls.
>
> "Verma, Lohit" <Loh...@hp...> wrote:
>
> Hi
> I have a question regarding constructors and destructors, and about class
pointers
> If I have a class A (see below), Now the second call crashes
>
> Also I can call a member function without allocating memory for a class
object.
>
> Please see code below and advice.
>
> Thanks a lot
>
> Lohit
>
>
>
> #include <iostream>
> using namespace std;
>
> class A{
>
> public:
> A(){
> delete this;
> }
> ~A(){
> cout<<"~A";
> }
>
> f(){
>
> cout<<"HELLO\n";
>
> }
>
> };
>
> int main()
> {
>     A *a=new A();//works
>
> It works because you have alloated the object a from heap and the 'delete'
operator works correctly in this case.
>
>
>     A b;//crashes why?? how is it any different from above.
>
> This crashes beacuse a is allocated from stack or compile time memory, so
any attempt to explicitly delete it will result in a crash.
>
>         A *c;
>
>                 c->f();//works why when I have not allocated any memory
for this.
>
> The third part got me stumped!!! I am attaching a code, the results are
strange on devcpp!
>
> }
>
>
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>
> Thanx and Regards
>    Avik Ghose
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