Re: [Dev-C++] Single Linked List Problem-II

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

Before going for how to use free(), let's have a look at how you use
malloc()...

See below:

/Per W


On Thu, 5 Jun 2003, Andr=E9 Mac=E1rio Barros wrote:

>
> I forgot the "int i;" variable declaration, ok?
> And this is a "C" program (aswering for the orientation "allways say if y=
ou
> are working
> with a C or C++ program").
>
> -----Mensagem original-----
> De: Andr=E9 Mac=E1rio Barros [mailto:and...@su...]
> Enviada em: quinta-feira, 5 de junho de 2003 22:58
> Para: Dev-Cpp-Users
> Assunto: Single Linked List Problem
>
>
> Dear Users,
>
> I need to discover a way to use the "free" command to correctly avoid 5
> records dinamically allocated in a simple Single Linked List program.
> Here are some pieces of it:
>
> ...
>
> #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 **);
>
> ...
> int main()
> {
>
>    struct address *info, *start, *last;
>
PWM: Here you allocate a buffer to start
>    init(&start);
PWM: And here you trow away your reference to it by setting start to NULL
>    start=3DNULL;
PWM: Here you allocate a buffer to last
>    init(&last);
PWM: And here the second buffer is thrown away
>    last=3DNULL;
>    for(i=3D0; i<MAX; i++)
>    {
>       init(&info);
>       printf("Enter name: ");
>       gets(info->name);
>       printf("Enter phone: ");
>       gets(info->phone);
>       slstore(info, &start, &last);
>    }
>    ...
>    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;
> }
>
> void init(struct address **arg)
> {
>    *arg=3D malloc(1*sizeof(struct address));
>    if(!(*arg))
>    {
>       printf("sem mem=F3ria\n");
>       system("PAUSE");
>       exit(EXIT_FAILURE);
>    }
PWM: Should initialize the allocated address too:
     *arg->next =3D NULL;
     *arg->name[0] =3D '\0';
     *arg->phone[0] =3D '\0';
> }
>

PWM: Try something like:

    // No need to allocate anything until you read in entries.
    start =3D last =3D NULL;

    for (...) {
        init(&info);
        ...

        if (!start) {
            start =3D last =3D info;
        } else {
            last->next =3D info;
            last =3D info;
        }
    }


PWM: To then release everything do:
    while (start) {
        info =3D start;
        start =3D start->next;
        free(info);
    }

> ***
> The slstore function stores the new element in the last position. It=B4s
> "next" record is filled
> with the NULL address to mean that there aren=B4t more elements in the li=
st.
> At the end of the program 5 memory spaces of 64 bytes each one, are
> allocated for each element.
> How can I use the free command to return the memory for the computer?
>
> Thanx
> Andre
>
>
>
>
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