/* This Queue implementation of singly linked list in C implements 3
* operations: add, remove and print elements in the list. Well, actually,
* it implements 4 operations, lats one is list_free() but free() should not
* be considered the operation but a mandatory practice like brushing
* teeth every morning, otherwise you will end up loosing some part of
* your body(the software) Its is the modified version of my singly linked
* list suggested by Ben from comp.lang.c . I was using one struct to do
* all the operations but Ben added a 2nd struct to make things easier and
* efficient.
*
* I was always using the strategy of searching through the list to find the
* end and then addd the value there. That way list_add() was O(n). Now I
* am keeping track of tail and always use tail to add to the linked list, so
* the addition is always O(1), only at the cost of one assignment.
*
*
* VERISON 0.5
*
*/
#include "queue.h"
/* Will always return the pointer to my_list */
struct my_list* list_add_element(struct my_list* s, struct SPE_instruction* i)
{
struct my_struct* p = malloc( 1 * sizeof(*p) );
if( NULL == p )
{
fprintf(stderr, "IN %s, %s: malloc() failed\n", __FILE__, "list_add");
return s;
}
p->num = i;
p->next = NULL;
if( NULL == s )
{
printf("Queue not initialized\n");
return s;
}
else if( NULL == s->head && NULL == s->tail )
{
/* printf("Empty list, adding p->num: %d\n\n", p->num); */
s->head = s->tail = p;
return s;
}
else if( NULL == s->head || NULL == s->tail )
{
fprintf(stderr, "There is something seriously wrong with your assignment of head/tail to the list\n");
free(p);
return NULL;
}
else
{
/* printf("List not empty, adding element to tail\n"); */
s->tail->next = p;
s->tail = p;
}
return s;
}
/* This is a queue and it is FIFO, so we will always remove the first element */
struct my_list* list_remove_element( struct my_list* s )
{
struct my_struct* h = NULL;
struct my_struct* p = NULL;
if( NULL == s )
{
printf("List is empty\n");
return s;
}
else if( NULL == s->head && NULL == s->tail )
{
printf("Well, List is empty\n");
return s;
}
else if( NULL == s->head || NULL == s->tail )
{
printf("There is something seriously wrong with your list\n");
printf("One of the head/tail is empty while other is not \n");
return s;
}
h = s->head;
p = h->next;
free(h);
s->head = p;
if( NULL == s->head ) s->tail = s->head; /* The element tail was pointing to is free(), so we need an update */
return s;
}
/* ---------------------- small helper fucntions ---------------------------------- */
struct my_list* list_free( struct my_list* s )
{
while( s->head )
{
list_remove_element(s);
}
return s;
}
struct my_list* list_new(void)
{
struct my_list* p = malloc( 1 * sizeof(*p));
if( NULL == p )
{
fprintf(stderr, "LINE: %d, malloc() failed\n", __LINE__);
}
p->head = p->tail = NULL;
return p;
}
