FIFO using pointers

AquamaN · 03-20-2004, 03:09 PM

Can someone show me show me how to create a basic First in First out (FIFO) waiting line using pointers? It needs to be dynamic because I don't know how many users are going to go into the FIFO line. I wrote one a long time ago for a program and I'm so rusty with pointers that I can't remember how do it. Thanks a lot!!

-AquamaN

aluser · 03-21-2004, 05:15 PM

You're going to have a structure like

Code:

struct fifo_element {
    struct fifo_element *next;
    void *data;
};

Then you can represent the whole FIFO as

Code:

struct fifo {
    struct fifo_element *head;
    struct fifo_element *tail;
};

To add a fifo_element *foo to a fifo bar,

Code:

struct fifo_element *foo = malloc(sizeof(*foo));
if (foo == NULL)
    barf();
foo->next = NULL;
foo->data = my_important_data;
bar.tail->next = foo;
bar.tail = foo;

To pop the first fifo_element from bar,

Code:

struct fifo_element *old = bar.head;
bar.head = bar.head->next;
free_fifo_element(old);

There are special cases when the fifo is empty, since you should have head and tail == NULL, and of course you don't want to dereference that. I leave those to you

AquamaN · 03-21-2004, 05:51 PM

Thanks a lot!!! You've helped me remember A LOT. Thanks once again!

-AquamaN