Re: create an object with variable CLASS

[Axel Freyn <axel-freyn at gmx dot de>]

Hi,
On Wed, Oct 28, 2009 at 06:07:32AM +0330, Mohsen Pahlevanzadeh wrote:
> You caused i open OOP in C++ book & start reading.My skill is python
> programming & C.
> But i have a question about previos source:
> When i compile my source, i get seg fau, When i run it with gdb, i rcv
> following message:
> _IO_vfscanf () from /lib/i686/cmov/libc.so.6
> Then i changed create_object to following code :
> module_management* create_object(char * class_name){
>         if (c_find(class_name) == NULL){
>                 if (strcmp (class_name,"mikrotik") == 0){
>                         mikrotik *iu ;
>                         return iu;//new mikrotik;
>                 }//end of strcmp
>         }//end of c_find if block
>         exit(1);
> }//end of func
> /////////////////////////////////////
> 
> When i compile it, i use following error with GDB:
> 250		create_object("mikrotik")->printg();
> Current language:  auto
> 
> /////////////////////////////////////////////////////
> I guess it return same Base object, because i tested with following
> function:
> cout <<typeid(create_object("mikrotik")).name() << endl;
> and i see it printed type of Base classs of mikrotik.
>  
> Do you have any idea?
We can't tell you all errors - therefore it would be necessary that you
send the complete source code. The best is always a file as short as
possible which contains all parts of the source code to produce the error.
However, there is at least one error in your code:
mikrotik *iu ;
return iu;//new mikrotik;
"iu" is a pointer to an object of class mikrotik. Then you return "iu".
However, you DON'T CREATE the object by using "new" - in this situation,
it is completely undefined what happens when you access "iu".
You have to write either:
mikrotik *iu ;
iu = new mikrotik;
return iu;

or
return new mikrotik;
or 
mikrotik *iu = new mikrotik;
return iu;
or something like that 

Axel.
> 
> 
> 
>  
> On Wed, 2009-10-28 at 03:11 +0330, Mohsen Pahlevanzadeh wrote:
> > Oh, shit, Thank you Andrew & Axel.
> > On Tue, 2009-10-27 at 11:34 +0000, Andrew Haley wrote:
> > > Mohsen Pahlevanzadeh wrote:
> > > > My main file:
> > > > int main(){
> > > > 	module_management *x;
> > > > 	x.printg();
> > > > }
> > > 
> > > Well, that's not going to work, is it?  x is a pointer, not
> > > an object.  You need
> > > 
> > >    x = create_object("mikrotik");
> > >    x->printg();
> > > 
> > > Andrew.
> > 
> > 
>