RE: [Dev-C++] Single Linked List-IV

[Per W. <pw...@ia...>]

The slstore() function DOES need it's last line, or else the list will not
get a pointer to the last element. The pointer to the last element is used
to allow insert of new elements last, without having to iterate throught
the list.

I know it's a bit extra noisy with dual indirection, but since the code
is C and not C++, slstore() can't take references to pointers.

/Per W

On Sat, 7 Jun 2003, Ioannis Vranos wrote:

> > -----Original Message-----
> > From: dev...@li...
> > [mailto:dev...@li...] On Behalf
> > Of Andr? Macario Barros
> > Sent: Friday, June 06, 2003 3:16 PM
> > To: Dev-Cpp-Users
> > Subject: [Dev-C++] Single Linked List-IV
> >
> >
> > Dear users,
> >    Please consider this (modificated) Single Linked List Code:
> >
> >
> > #include <stdio.h>
> > #include <stdlib.h>
> >
> > #define MAX 5
> >
> > struct address
> > {
> >    char name[40];
> >    char phone[20];
> >    struct address *next;
> > };
> >
> > void slstore(struct address *, struct address **, struct address **);
> > void display(struct address *);
> > void list(struct address **);
> > void init(struct address **);
> >
> > int main()
> > {
> >    struct address *info=3DNULL, *start=3DNULL, *last=3DNULL;
> >    int i;
> >
> >    for(i=3D0; i<MAX; i++)
> >    {
> >       init(&info);
> >       printf("Enter name: ");
> >       gets(info->name);
>
>
> Dangerous, you can't expect the user to know the internals of your code a=
nd
> limit himself to 39 characters. Use fgets() instead. Avoid gets() in
> general.
>
> fgets(info->name, 40, stdin);
>
>
> >       printf("Entre com phone: ");
> >       gets(info->phone);
>
>
> fgets(info->phone, 20, stdin);
>
>
> >       slstore(info, &start, &last);
> >    }
> >    printf("List Recorded:\n");
> >    list(&start);
> >    while (start)
> >    {
> >       info =3D start;
> >       start =3D start->next;
> >       free(info);
> >    }
> >    system("PAUSE");
> >    return(0);
> > }
> >
> > void slstore(struct address *i, struct address **start_arg,
> >              struct address **last_arg)
> > {
> >    if(*last_arg=3D=3DNULL)
>            *start_arg=3Di;
> >    else
>            (*last_arg)->next=3Di;
>
> >    i->next=3DNULL;
> >    *last_arg=3Di;
> > }
>
>
> I made the above more readable so as to understand it. Why do you use str=
uct
> **s and not struct *s and avoid those *s?
>
> I cannot understand the last line, it seems to contradict with the else
> statement at least. I suspect a bug here. Ommiting the last line it becom=
es:
>
> void slstore(struct address *i, struct address *start_arg,
>              struct address *last_arg)
> {
>    if(last_arg=3D=3DNULL)
>       start_arg=3Di;
>
>     else
>         last_arg->next=3Di;
>
>    i->next=3DNULL;
> }
>
>
>
> >
> > void display(struct address *info)
> > {
> >    printf("Actual address-->%p\n", info);
>
> When you pass a different pointer than expected in a variadic function yo=
u
> must cast:
>
> printf("Actual address-->%p\n", (void *)info);
>
>
>
>
> >    printf("%s\n", info->name);
> >    printf("%s\n", info->phone);
> >    printf("Next address-->%p\n", info->next);
>
>
> printf("Next address-->%p\n", (void *) info->next);
>
>
> >    printf("\n");
> >    system("PAUSE");
> > }
> >
> > void list(struct address **start_arg)
> > {
> >    struct address *info;
> >
> >    init(&info);
> >    info =3D *start_arg;
> >    while(info)
> >    {
> >       display(info);
> >       info =3D info->next;
> >    }
> > }
>
>
> You use **s while they are not needed in the whole program.
>
>
>
>
> > void init(struct address **arg)
> > {
> >    *arg=3D malloc(1*sizeof(struct address));
> >    if(!(*arg))
> >    {
> >       printf("sem mem=F3ria\n");
> >       system("PAUSE");
> >       exit(EXIT_FAILURE);
> >    }
> > }
>
>
> The same here. Without **s:
>
>
> void init(struct address *arg)
> {
>    arg=3D malloc(sizeof(*arg));
>
>    if(!arg)
>    {
>       printf("He was a good man, always to remember him\n");
>       system("PAUSE");
>       exit(EXIT_FAILURE);
>    }
> }
>
>
> > =3D=3D>My questions:
> > A) One example of addresses that are printed on the screen are:
> >    002224C8
> >    00222510
> >    00222558
> >    002225A0
> >    002225E8
> >    The distance between theese addresses is 72 bytes, not 64
> > as expected
> >    because the size of the struct address.
> >    WHY?
>
>
>
> If I recall correctly you create them on the free store, so their address
> can be anywhere.
>
>
>
>
>
> >
> > B) Could the final loop:
> >    while (start)
> >    {
> >       info =3D start;
> >       start =3D start->next;
> >       free(info);
> >    }
> >    be changed by a function call for a function like
> >
> >    free_ptr(&start);
> >
> >    void free_ptr(struct address **arg)
> >    {
> >       struct address *info=3DNULL;
> >
> >       while (*arg)
> >       {
> >          info =3D *arg;
> >          *arg =3D (*arg)->next;
> >          free(info);
> >       }
> >    }
>
>
> Yes, isn't it exactly the same with the unneeded use of **s? Better:
>
>
> void free_ptr(struct address *arg)
> {
>     struct address *info;
>
>     while (arg)
>     {
>        info =3D arg;
>        arg =3D arg->next;
>        free(info);
>     }
> }
>
>
>
>
>
>
> Ioannis Vranos
>
> * Programming pages: http://www.noicys.freeurl.com
> * Alternative URL 1: http://run.to/noicys
> * Alternative URL 2: http://www.noicys.cjb.net
>
>
>
>
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