c - stailq - tailq_first

Minimal example of TAILQ usage out of<sys/queue.h> library (1)

Can some one provide minimal example of TAILQ usage out of linux system library with explanation in c which can be compiled using gcc in Linux?

The TAILQ_ENTRY macro is used to establish the pointers used to insert items into the list. You place it into your structure that you want to list up.

struct foo {
    TAILQ_ENTRY(foo) tailq;
    int datum;
    /* ... */

The TAILQ_HEAD is used to define a structure that will act as the container for your link list elements. You provide it with a structure name, and the name of the type that it will contain.

TAILQ_HEAD(fooq, foo);

Use TAILQ_INIT to initialize an instance of your list container.

struct fooq q;

Use the TAILQ_INSERT_* macros to add elements.

struct foo data[3] = { foo(3), foo(7), foo(1) };
TAILQ_INSERT_HEAD(&q, &data[0], tailq);
TAILQ_INSERT_AFTER(&q, &data[0], &data[1], tailq);
TAILQ_INSERT_TAIL(&q, &data[2], tailq);

You can use TAILQ_FOREACH and TAILQ_FOREACH_REVERSE to traverse the list.

struct foo *p;
TAILQ_FOREACH(p, &q, tailq) {
    printf(" %d", p->datum);

If you want to iterate over the list while removing all its elements, it is probably easier to use a while loop and use the TAILQ_EMPTY and TAILQ_FIRST macros.

while (!TAILQ_EMPTY(&q)) {
    p = TAILQ_FIRST(&q);
    TAILQ_REMOVE(&q, p, tailq);
    /* ... */

The above code was mostly taken verbatim from an example I wrote and tested on IDEONE.