Thread: Help free structs and pointer.

hm you kind of lost me there.
So I have this list LIST_ELEM which holds a bunch of structs

pHead <-strct1<-strct2

and when I remove it i want it to look like

pHead<-struct2

or in the first case

pHead<-strct1

remove returns

pHead


but i'm not getting anything like that, I'm getting my original list when print it out, or find the size

So run the following code and play "spot the parallel":

Code:

void func1(int bob) {
    bob = 6;
}

void func2(int *bob) {
    bob = NULL;
}

int main(void) {
    int i = 11;
    int *iptr = &i;
    func1(i);
    printf("%d\n", i);
    func2(iptr);
    if (iptr == NULL) printf("Variable successfully removed.\n");
    printf("%p\n", iptr);
    return 0;
}

11 and an address is returned.

so i basically can't set something to null and say it was removed.

Even though you pass in a pointer to the function, that means you can only change the value of what is pointed to, not the value of the pointer itself (that's just a copy). So if you want to change the value of the pointer, which it seems like you do, you'll have to add an extra *.

So if:

LIST_ELEM *ptr = pHead;

and I want to free the actual item at *ptr

i would have to use

free(**ptr)? doesn't that return an invalid type error?

No you would have to use

Code:

void removePtr(LIST_ELEM **pHead, int loc)

and adjust accordingly.

Man that would make it more difficult for me.

so taking in a *pHead and then setting equal to say

Code:

 LIST_ELEM **ptr = pHead

You could do that but you're back where you started -- pHead wouldn't change just because you changed ptr.

I'm starting to worry a little bit -- all the list functions require a elem** to work (creating, adding, deleting, ...)

EDIT: And for that matter, it's not as though the change is hard: do a search-and-destroy turning pHead to *pHead everywhere in the function and you're done!

LOL you're beginning to worry me now. I've been using (LIST_ELEM *pHead) for my add, print, and find methods.

Well, okay, print just takes one star. Find could take one * if you're not trying to change the list. But if you add something to the front of the list and try to change pHead = just_created_element, that won't work.

so my program is a fluke since I use one * for add, and sizeOf returns the right size after adding in an element.

Are you in a special case where you are always adding at the end or something?

always adding to the front