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

[Ioannis V. <iv...@em...>]

> -----Original Message-----
> From: dev...@li...=20
> [mailto:dev...@li...] On Behalf=20
> Of Andr? Macario Barros
> Sent: Friday, June 06, 2003 3:16 PM
> To: Dev-Cpp-Users
> Subject: [Dev-C++] Single Linked List-IV
>=20
>=20
> Dear users,
>    Please consider this (modificated) Single Linked List Code:
>=20
>=20
> #include <stdio.h>
> #include <stdlib.h>
>=20
> #define MAX 5
>=20
> struct address
> {
>    char name[40];
>    char phone[20];
>    struct address *next;
> };
>=20
> void slstore(struct address *, struct address **, struct address **);
> void display(struct address *);
> void list(struct address **);
> void init(struct address **);
>=20
> int main()
> {
>    struct address *info=3DNULL, *start=3DNULL, *last=3DNULL;
>    int i;
>=20
>    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 =
and
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);
> }
>=20
> 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 =
struct
**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 =
becomes:

void slstore(struct address *i, struct address *start_arg,
             struct address *last_arg)
{
   if(last_arg=3D=3DNULL)=20
      start_arg=3Di;
  =20
    else
        last_arg->next=3Di;
  =20
   i->next=3DNULL;
}



>=20
> void display(struct address *info)
> {
>    printf("Actual address-->%p\n", info);

When you pass a different pointer than expected in a variadic function =
you
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");
> }
>=20
> void list(struct address **start_arg)
> {
>    struct address *info;
>=20
>    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=20
> 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.





>=20
> 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
>=20
>    free_ptr(&start);
>=20
>    void free_ptr(struct address **arg)
>    {
>       struct address *info=3DNULL;
>=20
>       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;
=20
    while (arg)
    {
       info =3D arg;
       arg =3D arg->next;
       free(info);
    }
}






Ioannis Vranos
=20
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