FIFO (first in first out) queue structure

Structs

Queue is a linked list with queue-based operations available

#define Queue List

Functions

queue_init

Initializes the queue. The user is responsible for creating the initial Queue structure and freeing memory with queue_destroy(). destroy is a deallocation function for the members of Queue, pass NULL if the memory is stack-allocated

void queue_init(Queue *queue, void (*destroy)(void *data));

/* Usage */
Queue *queue = malloc(sizeof(Queue));

// Pass NULL for stack-allocated memory
queue_init(queue, NULL);

// Pass free or a custom freeing function for heap allocated memory
queue_init(queue, free);

queue_destroy

Destroys the nodes inside a Queue and calls the deallocation function on the data if one was provided. Does not destroy the queue itself, that is left up to the user.

void queue_destroy(Queue *queue);

queue_enqueue

Adds an element to the back of the queue. Returns 0 on success, -1 on error.

int queue_enqueue(Queue *queue, const void *data);

/* Usage */
int a = 1;
queue_enqueue(queue, &a);

queue_dequeue

Removes the element at the front of the queue and stores its data in data. Returns 0 on success, -1 if the queue is empty.

int queue_dequeue(Queue *queue, void **data);

/* Usage */
// queue: 1 2 3
int *t;
queue_dequeue(queue, (void **)&t);
assert(*t == 1);
// queue: 2 3

queue_peek

Returns a void * to the front element of the queue without removing it. Returns NULL if the queue is empty.

void *queue_peek(Queue *queue);

/* Usage */
// queue: 1 2 3
int *t = (int *)queue_peek(queue);
assert(*t == 1);
// queue: 1 2 3

Macros

queue_size

Returns the number of elements in the queue.

#define queue_size(q) ((q)->size)

queue_is_empty

Returns true if the queue has no elements.

#define queue_is_empty(q) ((q)->size == 0)