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

[<and...@su...>]

Crucial help!!!
Terrific!

Thank you
André

-----Mensagem original-----
De: Per Westermark [mailto:pw...@ia...]
Enviada em: sexta-feira, 6 de junho de 2003 09:44
Para: André Macário Barros
Cc: Dev-Cpp-Users
Assunto: Re: [Dev-C++] Single Linked List-IV




On Fri, 6 Jun 2003, André Macário Barros wrote:

> 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=NULL, *start=NULL, *last=NULL;
>    int i;
>
>    for(i=0; i<MAX; i++)
>    {
>       init(&info);
>       printf("Enter name: ");
>       gets(info->name);
>       printf("Entre com phone: ");
>       gets(info->phone);
>       slstore(info, &start, &last);
>    }
>    printf("List Recorded:\n");
>    list(&start);
>    while (start)
>    {
>       info = start;
>       start = start->next;
>       free(info);
>    }
>    system("PAUSE");
>    return(0);
> }
>
> void slstore(struct address *i, struct address **start_arg,
>              struct address **last_arg)
> {
}
>    if(*last_arg==NULL) *start_arg=i;
>    else (*last_arg)->next=i;
>    i->next=NULL;
>    *last_arg=i;
> }
>
> void display(struct address *info)
> {
>    printf("Actual address-->%p\n", info);
>    printf("%s\n", info->name);
>    printf("%s\n", info->phone);
>    printf("Next address-->%p\n", info->next);
>    printf("\n");
>    system("PAUSE");
> }
>
> void list(struct address **start_arg)
> {
>    struct address *info;
>
PWM: Don't allocate any info - the list already contains the entries, and
PWM: you only want to use info as a pointer poiting to the entries
PWM: available in  the list.
PWM: Remove this line.>    init(&info);
>    info = *start_arg;
>    while(info)
>    {
>       display(info);
>       info = info->next;
>    }
> }
>
> void init(struct address **arg)
> {
>    *arg= malloc(1*sizeof(struct address));
>    if(!(*arg))
>    {
>       printf("sem memória\n");
>       system("PAUSE");
>       exit(EXIT_FAILURE);
>    }
> }
>
> ==>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?

PWM: Because the memory library have to allocate some extra space for
book-keeping. Normally malloc() will store the size of the memory block (4
byte) and a pointer to the previously allocated block (4 byte).

>
> B) Could the final loop:
>    while (start)
>    {
>       info = start;
>       start = 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=NULL;
>
>       while (*arg)
>       {
>          info = *arg;
>          *arg = (*arg)->next;
>          free(info);
>       }
>    }
PWM: Yes, but you might consider adding a line
PWM: *arg = NULL;
PWM: to make sure that the caller knows that start doesn't point to any
PWM: elements anymore.

>
> Thanks
> Andre
>
>
>
>
>
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