C 언어 --- - 링크 에 고리 가 있 는 지 판단

#include <stdio.h>
#include <stdlib.h>

#define CNT 10

typedef struct node{
	int value;
	struct node *next;
}list_node_t;

list_node_t *creat_node(int value);

void list_print_node(list_node_t *node_p);
void list_print_all(list_node_t *node_p);

list_node_t *list_insert_end_node(list_node_t *node_p, int value);
void list_is_ring(list_node_t *node_p);

void list_free(list_node_t *node_p);

int main(int argc, char **argv)
{
	int i;
	list_node_t *head = NULL;

	for(i = 0; i < CNT; i++)
	{
		head = list_insert_end_node(head, i+1);
	}
	list_print_all(head);

	list_is_ring(head);

	list_free(head);

	return 0;
}

list_node_t *creat_node(int value)
{
	list_node_t *node_p;

	node_p = malloc(sizeof(list_node_t));
	if(node_p == NULL)
	{
		fprintf(stderr, "Malloc for creating node failed.
");
		exit(1);
	}

	node_p->value = value;
	node_p->next = NULL;

	return node_p;
}

void list_print_node(list_node_t *node_p)
{
	fprintf(stdout, "p = %p value = %2d p->next = %p
", node_p, node_p->value, node_p->next);
}

void list_print_all(list_node_t *node_p)
{
	list_node_t *head = node_p;

	while(head)
	{
		list_print_node(head);
		head = head->next;

		if(head == node_p)
			break;
	}
}

list_node_t *list_insert_end_node(list_node_t *node_p, int value)
{
	list_node_t *new_node = creat_node(value);

	if(new_node == NULL)
	{
		fprintf(stderr, "Creat new node failed.
");
		exit(1);
	}

	if(node_p == NULL)
	{
		node_p = new_node;
		new_node->next = node_p;
		return node_p;
	}

	list_node_t *p = node_p;
	while(p->next)
	{
		p = p->next;
		if(p->next == node_p)
			break;
	}

	p->next = new_node;
	new_node->next = node_p;

	return node_p;
}

void list_is_ring(list_node_t *node_p)
{
	list_node_t *prev, *cur;

	prev = cur = node_p;

	while(1)
	{
		prev = prev->next;
		//cur = cur->next->next;

		if(prev == NULL)
		{
			fprintf(stdout, "Is not ring.
");
			break;
		}
		else
		{
			fprintf(stdout, "Is ring.
");
			break;
		}
	}
}

void list_free(list_node_t *node_p)
{
	list_node_t *p = node_p;

	while(p->next)
	{
		if(p->next == node_p)
			break;
		free(p);
		p = p->next;
	}
	free(p);
}