//栈的链式存储企业版（即结点只维护指针域，数据域由用户自己维护）
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

//结点的结构体
struct stackNode{
    struct stackNode *next; //只维护指针域
};

//栈的结构体
struct  LStack{
    struct stackNode pHeader;
    int m_size;
};

typedef void * LinkStack;

//初始化链栈
//头结点端做栈顶，方便出栈入栈。因为尾端做栈顶每次出栈入栈都要遍历找尾结点。
LinkStack init_stack(){
    struct LStack *mylstack=malloc(sizeof(struct LStack));
    if (mylstack==NULL)
    {
        return NULL;
    }
    mylstack->pHeader.next=NULL;
    mylstack->m_size=0;
    return mylstack;
}

//入栈
void push_stack(LinkStack lstack,void *data){
    if (lstack==NULL)
    {
        return;
    }
    if (data==NULL)
    {
        return;
    }
    struct LStack *mylstack=lstack;

    //将用户数据取前四个字节用
    struct stackNode *pNode=data;

    pNode->next=mylstack->pHeader.next;
    mylstack->pHeader.next=pNode;

    //更新链表长度
    mylstack->m_size++;
}

//出栈
void pop_LinkStack(LinkStack stack)
{
	//出栈本质 --- 链表头删
	if (stack == NULL)
	{
		return;
	}

	struct LStack * myStack = stack;

	if (myStack->m_size == 0) //栈为空
	{
		return;
	}

	//更改指针指向
	//缓存第一个有数据节点
	struct stackNode * pFirst = myStack->pHeader.next;

	myStack->pHeader.next = pFirst->next;

	//更新栈大小
	myStack->m_size--;

}

//返回栈顶元素
void * top_LinkStack(LinkStack stack)
{
	if (stack == NULL)
	{
		return NULL;
	}
	struct LStack * myStack = stack;

	if (myStack->m_size == 0)
	{
		return NULL;
	}

	return myStack->pHeader.next;

}

//返回栈个数
int size_LinkStack(LinkStack stack)
{
	if (stack == NULL)
	{
		return -1;
	}
	struct LStack * myStack = stack;

	return myStack->m_size;
}

//判断是否为空
int isEmpty_LinkStack(LinkStack stack)
{
	if (stack == NULL)
	{
		return -1;
	}
	struct LStack * myStack = stack;

	if (myStack->m_size == 0)
	{
		return 1;
	}

	return 0;
}

//销毁
void destroy_LinkStack(LinkStack stack)
{
	if (stack == NULL)
	{
		return;
	}
	free(stack);
	stack = NULL;
}