myqueue.h

// This header file provides a basic queue implementation

// ========== Forward Declarations ==========

// create and empty-initialize the queue
void create();

// returns 1 if queue is empty, 0 otherwise
int empty();

// returns the length of the queue
unsigned size();

// insert an element at the back of the queue
void push(unsigned value);

// get the first element from the front of the queue
unsigned front();

// remove the first element from the front of the queue
void pop();

// ========== Implementation Detail ==========

#include <sys/queue.h>  // provides the internal queue implementation

unsigned myQueueLength = 0;

STAILQ_HEAD(stailhead, entry) head = STAILQ_HEAD_INITIALIZER(head);

struct stailhead* headp;

struct entry {
    unsigned content;
    STAILQ_ENTRY(entry) entries;
};

void create() { STAILQ_INIT(&head); }

int empty() { return STAILQ_EMPTY(&head); }

unsigned size() { return myQueueLength; }

void push(unsigned value) {
    struct entry* myElement = malloc(sizeof(struct entry));
    myElement->content = value;
    STAILQ_INSERT_TAIL(&head, myElement, entries);
    myQueueLength++;
}

unsigned front() {
    struct entry* myElement = STAILQ_FIRST(&head);
    return myElement->content;
}

void pop() {
    struct entry* myElement = STAILQ_FIRST(&head);
    STAILQ_REMOVE_HEAD(&head, entries);
    free(myElement);
    myQueueLength--;
}