Re: [Dev-C++] Crash with macro to template conversion
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Re: [Dev-C++] Crash with macro to template conversion
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From: Per W. <pw...@ia...> - 2004-02-29 01:19:57
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Yes, you can continue to cascade the pointers to pointers to... but with a
correctly written program you never need to since the goal of the program
is to either move the pointer or what the pointer points to.
/Per W
On Sat, 28 Feb 2004, David McKen wrote:
> Thanks,
>
> Just a question for future refrence but can the "pointer to" chain go
> infinitely?
> i.e.
> Does char *** x make a pointer-to-a-pointer-to-a-pointer-to-a-char ?
>
> Also refrences cannot be chained, right? That would be the logical
> AND
> operator anyway.
>
> ----- Original Message -----
> From: "Per Westermark" <pw...@ia...>
> To: "David McKen" <ci...@ya...>
> Cc: "Mailing List, Dev-Cpp" <dev...@li...>
> Sent: Saturday, February 28, 2004 3:20 PM
> Subject: Re: [Dev-C++] Crash with macro to template conversion
>
>
> > Oops. Too quick answer :-)
> > With the following construct, the caller will get back the newly
> allocated
> > pointer:
> >
> > void alloc(char*& ptr) {
> > ptr = new char[10];
> > }
> >
> > int main() {
> > char *ptr = NULL;
> > printf("ptr = %p\n",ptr);
> > alloc(ptr);
> > printf("ptr = %p\n",ptr);
> > return 0;
> > }
> >
> > /Per W
> >
> > On Sat, 28 Feb 2004, David McKen wrote:
> >
> > > you apparently did not read the end of my message,
> > >
> > > I know how to create a pointer to a pointer (**) I haven't heard
> > > about a
> > > refrence to a pointer (&* ?), what is the syntax for such a
> variable?
> > >
> > > ----- Original Message -----
> > > From: "Per Westermark" <pw...@ia...>
> > > To: "David McKen" <ci...@ya...>
> > > Cc: "Mailing List, Dev-Cpp" <dev...@li...>
> > > Sent: Saturday, February 28, 2004 5:27 AM
> > > Subject: 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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