On 6 May, 03:33, "Michael.Z" <zhangqiuy...@[EMAIL PROTECTED]
> wrote:
> Hi Flash Gordon:
> The Table.c was required to be implemented as generic type.
I'm not sure what a "generic type" is and I have been programming
for quite a while.
>=A0If I am
> right, Table is declared as void * in header file, the reason is that,
> when used later on, it can be casted to any other type of pointers.
It may be you trying to hide implementation details from users
of your code. The outside world uses a void* and your
code (the library) casts it to the right type before use.
This is good. The internal data structure can change
without causing a recompile of the user code.
/* pippo.h */
typedef void* Table_handle;
Table_handle create();
void befunge (Table_handle);
/* pippo.c */
void befunge (Table_handle handle)
{
Table* table =3D (Table*)handle;
...
}
/* user.c */
int main (void)
{
Table_handle* my_table;
my_table =3D create();
befunge(my_table);
return 0;
}
The point is I *don't* try and have two differing
definitions of Table.
> The implementation of Table in Table.c was defined as pointer to
> struct Table, because I need to implement the members of Table.
>
> My professor told us, void * in header indicates a generic type.
> He has some sample codes where List was typedef'd void pointer but the
> definition was struct List Pointer:
so he had two different types didn't he?
> /* Header file List.h*/
> #ifndef LIST_H
> #define LIST_H
>
> #include "bool.h"
>
> =A0 =A0 =A0 =A0 typedef void * List ;
> =A0 =A0 =A0 =A0 typedef void * DataL ;
> =A0 =A0 =A0 =A0 typedef void * ListIt ;
>
> =A0 =A0 =A0 =A0 List makeList ( int , void * (*copy)() , void (*free)()
) =
;
> =A0 =A0 =A0 =A0 void freeList ( List ) ;
> =A0 =A0 =A0 =A0 void clearList ( List ) ;
>
> =A0 =A0 =A0 =A0 boolean accessList ( List , DataL , int ) ;
> =A0 =A0 =A0 =A0 int lengthList ( List ) ;
>
> =A0 =A0 =A0 =A0 boolean accessHead ( List , DataL ) ;
> =A0 =A0 =A0 =A0 boolean insertHead ( List , DataL ) ;
> =A0 =A0 =A0 =A0 boolean deleteHead ( List , DataL ) ;
>
> =A0 =A0 =A0/* not all the header file is copied here*/
>
> /* List.c */
>
> #include "bool.h"
> #include <stdio.h>
> #include <stdlib.h>
>
> #ifndef DATA
> #define DATA
> typedef void * Data ;
> #endif
>
> typedef struct ListNode {
> =A0 =A0 =A0 =A0 struct ListNode * next ; =A0 =A0 =A0 =A0/* reference to
fo=
llowing ListNode */
> =A0 =A0 =A0 =A0 struct ListNode * previous ; =A0 =A0/* reference to
preced=
ing ListNode */
> =A0 =A0 =A0 =A0 Data dptr ;
>
> } ListNode ;
>
> typedef struct List {
> =A0 =A0 =A0 =A0 ListNode * head ; =A0 =A0 =A0 =A0 =A0 =A0 =A0 /* Head
end =
of List =A0 =A0 =A0 =A0 =A0 =A0 */
> =A0 =A0 =A0 =A0 ListNode * tail ; =A0 =A0 =A0 =A0 =A0 =A0 =A0 /* Tail
end =
of List =A0 =A0 =A0 =A0 =A0 =A0 */
> =A0 =A0 =A0 =A0 int _lengthList ; =A0 =A0 =A0 =A0 =A0 =A0 =A0 /* number
of=
items within List =A0*/
> =A0 =A0 =A0 =A0 int _sizeData ; =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 /* byte
si=
ze of data to be stored */
> =A0 =A0 =A0 =A0 void (*_freeData)( ) ; =A0 =A0 =A0 =A0 =A0/* returns
data =
item to heap =A0 =A0*/
> =A0 =A0 =A0 =A0 void * (*_copyData)( ) ; =A0 =A0 =A0 =A0/* copies data
ite=
m to another =A0*/
>
> } * List ;
arg!!!
don't top post. Please put your reply after the text you are
replying to.
> On May 3, 2:32 am, Flash Gordon <s...@[EMAIL PROTECTED]
> wrote:
>
>
>
> > Michael.Z wrote, On 03/05/08 08:22:
>
> > > Anyone who can help:
>
> > > Given a Table.h file I am writing a Table.c file.
> > > I keep getting the compile error:
>
> > > previous declaration of Table was here / =A0conflicting types for
>
> > > I think the problem was the result of two pieces of code.
> > > First:typedefstruct Table; =A0/* in Table.c*/
>
> > This says that Table is a struct.
>
> > > Second: struct Table { /*struct definition */ } =A0*Table; =A0/* in
> > > Table.h */
>
> > This says it is a pointer to a struct, that is what the * means.
>
> > > How can I solve the problems?
>
> > By not providing different definitions.
>
> > > Here are the two files
>
> > <snip>
>
> > >typedefvoid * Table ;
>
> > This is not what you said you had and is defining table as yet another
t=
ype.
>
> > <snip>
>
> > >typedefstruct Table{
> > > =A0 =A0 int sizeTable;
> > > =A0 =A0 unsigned sizeData;
> > > =A0 =A0 int (*diff)();
> > > =A0 =A0 unsigned (*hash)();
> > > =A0 =A0 void *(*copy)();
> > > =A0 =A0 void (*free)();
> > > } * Table;
>
> > This is what you said. However pointers to void and pointers to
structs
> > are different things for the simple reason that void and struct are
> > different.
>
> > Also hiding pointers behind atypedefis generally considered a bad
thing.=
> > --
> > Flash Gordon-
don't quote sigs (the bit after the "-- ")
--
Nick Keighley
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