Re: [Dev-C++] Crash with macro to template conversion

But you have not fixed the declaration of the ptr parameter yet. Any
allocations you make will behave ok inside the create() function, but the
caller will never get the value of the allocated pointer! You REALLY MUST
change del parameter declaration to either be a pointer to a pointer, or a
reference to a pointer!

/Per W

On Fri, 27 Feb 2004, David McKen wrote:

> Sorry about that the correct definition is:
> template<class T>
> void create(T * ptr, int number, char * f_name = __FILE__, int l_num
> =
> __LINE__)
> {
>   ptr = new T[number];
>   if ( !ptr )
>  {
>     perror("malloc failure");
>     fprintf( stderr, "Malloc failure @ %s:%d\n", f_name, l_num );
>     abort();
>   }
> }
>
> All the exception stuff was just trying to figure out if an error is
> even
> occuring.
>
> I am trying to keep to convention. The macro is not my code but code
> I am
> trying to replace. I am very tempted to change it but I also have
> RECREATE
> (wraps realloc()) and DESTROY (wraps free() ) which also need to be
> replaced. I could use macros to alter the function call but I am
> trying to
> remove all the macros I can (got some linked list macros to replace
> as well)
>
> So...How does one create a refrence to a pointer?
>
> ----- Original Message -----
> From: "Per Westermark" <pw...@ia...>
> To: "David McKen" <ci...@ya...>
> Cc: "Mailing List, Dev-Cpp" <dev...@li...>
> Sent: Friday, February 27, 2004 7:08 AM
> Subject: Re: [Dev-C++] Crash with macro to template conversion
>
>
> > First of all - your create template function is declared to return
> void,
> > so why do you end it with return ptr?
> >
> > Second, you send in a T* ptr parameter. Note that since C++ uses
> > call-by-value, this will behave like a lokal variable, i.e any
> assign to
> > ptr will not reflect back to the caller. You should change the
> first
> > parameter of create to be a reference to a pointer. That way, the
> assign
> > to ptr will reflect back to the variable obj of the caller.
> >
> > /Per W
> >
> > On Fri, 27 Feb 2004, David McKen wrote:
> >
> > > Ok here is my problem.
> > >
> > > I want to replace:
> > > #define CREATE(result, type, number)                \
> > > do                              \
> > > {                               \
> > >     if (!((result) = (type *) calloc ((number), sizeof(type)))) \
> > >     {                               \
> > >     perror("malloc failure");               \
> > >     fprintf(stderr, "Malloc failure @ %s:%d\n", __FILE__,
> __LINE__ );
> > > \
> > >     abort();                        \
> > >     }                               \
> > > } while(0)
> > >
> > > With it's C++ equivalent.
> > >
> > > So far I have:
> > > #define CREATE(result, type, num)    create<type>((result),(num))
> > > template<class T>
> > > void create(T * ptr, int number, char * f_name = __FILE__, int
> l_num
> > > =
> > > __LINE__)
> > > {
> > >   try {
> > >     ptr = new T[number];
> > >   }
> > >   catch(bad_alloc& b)
> > >   {
> > >     perror("malloc failure");
> > >     fprintf( stderr, "Malloc failure @ %s:%d\n", f_name, l_num );
> > >     abort();
> > >   }
> > >   if ( !ptr )
> > >   {
> > >     perror("malloc failure");
> > >     fprintf( stderr, "Malloc failure @ %s:%d\n", f_name, l_num );
> > >     abort();
> > >   }
> > >   return ptr;
> > > }
> > >
> > > But the program crashes after the function call when any attempt
> to
> > > acces
> > > the data occours:
> > > e.g.
> > > OBJ_DATA * obj;
> > > CREATE( obj , OBJ_DATA, 1 );
> > >
> > > obj->some_field = 5; //Crashes here and obj = 0x0 from gdb.
> > >
> > > Thanks in Advance
> > > David McKen
> > >
> > >
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