stack.c

calc大数库

/* File: stack.c
 * Desc: implementation of the Stack interface using opaque types.
 * Cristina Cifuentes
 * 13 Aug 1997
 */

#include <assert.h>
#include <stdlib.h>
#include "stack.h"

struct _Stack {
    int count;			/* # elements */
    struct elem {
	void        *x;		/* actual element */
	struct elem *link;	/* next element of the stack */
    } *head;
};


Stack stackNew (void)
{ Stack stk;

	stk = (Stack)malloc(sizeof(struct _Stack));
	stk->count = 0;
	stk->head = NULL;
	return stk;
}


int stackEmpty (Stack stk)
{
	assert (stk);
	return (stk->count == 0);
}


void stackPush (Stack stk, void *x)
{ struct elem *t;

	assert (stk);
	t = (struct elem *)malloc(sizeof(struct elem));
	t->x = x;
	t->link = stk->head;
	stk->head = t;
	stk->count++;
}


void *stackPop (Stack stk)
{ void *x;
  struct elem *t;

	assert (stk);
	assert (stk->count > 0);
	t = stk->head;
	stk->head = t->link;
	stk->count--;
	x = t->x;
	free (t);
	t = NULL;
	return x;
}


void stackFree (Stack *stk)
{ struct elem *t, *u;

	assert (stk && *stk);
	for (t = (*stk)->head; t; t = u)
	{
		u = t->link;
		free (t);
		t = NULL;
	}
	free (*stk);
	*stk = NULL;
}