Creating a new queue
We'd like our large programs to have more than a single queue -
thus we don't want a single, global, variable,
and we don't know until run-time how many queues we'll require.
We thus need a function to allocate space for,
and to initialize,
a new queue:
QUEUE *queue_new(void)
{
QUEUE *q = malloc( sizeof(QUEUE) );
if(q == NULL) {
perror( __func__ );
exit(EXIT_FAILURE);
}
q->head = NULL;
q->tail = NULL;
return q;
}
....
QUEUE *people_queue = queue_new();
QUEUE *truck_queue = queue_new();
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QUEUE *queue_new(void) // same outcome, often seen
{
QUEUE *q = calloc( 1, sizeof(QUEUE) );
if(q == NULL) {
perror( __func__ );
exit(EXIT_FAILURE);
}
return q;
}
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If we remember that:
- the calloc function both allocates memory
and sets all of its bytes to the zero-bit-pattern, and
- that (most) C11 implementations
represent the NULL pointer as the zero-bit-pattern,
then we appreciate the simplicity of allocating new items with calloc.
CITS2002 Systems Programming, Lecture 19, p14, 3rd October 2023.
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CITS2002