我的将两个顺序链表按顺序归并的sort函数为什么不成功？

求解答
代码如下：

#include<stdio.h>
#include<stdlib.h>
using namespace std;

//存储结构 
typedef struct LNode{
    int data;
    struct LNode *next;
}LNode, *LinkList;

//头插法建表 
LinkList creatlist()
{
    int data; LinkList head; LNode *p;
    head = NULL;
    
    int n;
    puts("请输入初始节点个数：");
    scanf("%d",&n);
    while(n--)
    {
        puts("请输入节点值：");
        scanf("%d",&data);
        p = (LNode *)malloc(sizeof(LNode));
        p->data = data;
        p->next = head;
        head = p;
    }
    puts("节点创建完成！");
    puts("");
    
    return head;
}

//尾插法建表
LinkList creatlist_tail()
{
    int data; LinkList head; LNode *p,*tail;
    
    p = (LNode *)malloc(sizeof(LNode));
    int n = 0;
    printf("请输出节点数值：\n");
    while(1)
    {
        scanf("%d",&data);
        if(data == 0) break;
        if(n == 0)
        {
            p->data =data;
            head = p;
            tail = p;
            p->next = NULL;
            n++;
        }
        else
        {
            p->data = data;
             tail->next = p;
             p->next = NULL;
             tail = p;
             n++;
        }
        p = (LNode *)malloc(sizeof(LNode));
    }
    return head;
} 

//按序号查找 
LNode *GetElem(LinkList head,int i)
{
    int j = 0;
    LNode *p = head;
    while(p->next&&j<i)
    {
        p = p->next;
        j++;
    }
    if(i == j) return p;
    else return NULL;
}

//在序号为x的数之前插入 
void InsertNode(LinkList head,int x,int e)
{
    LNode *p,*q;
    p = GetElem(head,x-1);
    
    //检验找到的节点 
    if(p == NULL)
    {
        puts("position error");
        return;
    } 
    
    
    q = (LNode *)malloc(sizeof(LNode));
    
    q->data = e;
    q->next = p->next;
    p->next = q;
}

//删除 
void DeletNode(LinkList head,int x)
{
    LNode *p,*q;
    p = GetElem(head,x-1);
    q = p->next;
    p->next = p->next->next;
    free(q);
}

//修改 
void ChangeNode(LinkList head,int x,int e)
{
    LNode *p;
    p = GetElem(head,x);
    p->data = e;
}

//遍历
void bianli(LinkList head)
{
    LNode *h = head;
    while(h!=NULL)
    {
        printf("%d ",h->data);
        h = h->next;
    }
    puts("");
} 

void sort(LinkList head1,LinkList head2,LinkList head3)
{
    LNode *p1,*p2,*p3;
    p1 = head1; p2 = head2;
    head3 = head1;
    p3 = head1;
    
    while(p1&&p2)
    {
        if(p1->data<=p2->data)
        {
            p3->next = p1; p3 = p1; p3->next = NULL; p1 = p1->next;
        }
        else
        {
            p3->next = p2; p3 = p2; p3->next = NULL; p2 = p2->next;
        }
    }
    p3->next = p1?p1:p2;
    free(head2);
}

int main()
{
    LinkList head = creatlist_tail();
    printf("当前链表1所有节点：\n");
    bianli(head);
    
    printf("查找序号为0的节点：\n");
    LNode *p = GetElem(head,0);
    printf("%d",p->data);
    puts("");
    
    printf("在序号为2的节点前插入数值为7的节点：\n");
    InsertNode(head,2,7);
    bianli(head);
    
    printf("删除当前序号为2的节点：\n");
    DeletNode(head,2);
    bianli(head);
    
    printf("将序号为0的节点值改为8：\n"); 
    ChangeNode(head,0,8);
    bianli(head);
    
    LinkList head2 = creatlist_tail();
    printf("当前链表2所有节点：\n");
    bianli(head2);
    
    LinkList head3;
    sort(head,head2,head3);
    
    //bianli(head3);
    puts("********************");
    LNode *p3 = GetElem(head3,0);
    printf("%d",p->data);
    puts("");
    return 0;
}

//1 2 3 4 5 0

修改如下，供参考：

#include<stdio.h>
#include<stdlib.h>
using namespace std;

//存储结构
typedef struct LNode{
    int data;
    struct LNode *next;
}LNode, *LinkList;

//头插法建表
LinkList creatlist()
{
    int data; LinkList head; LNode *p;
    head = NULL;

    int n;
    puts("请输入初始节点个数：");
    scanf("%d",&n);
    while(n--)
    {
        puts("请输入节点值：");
        scanf("%d",&data);
        p = (LNode *)malloc(sizeof(LNode));
        p->data = data;
        p->next = head;
        head = p;
    }
    puts("节点创建完成！");
    puts("");

    return head;
}

//尾插法建表
LinkList creatlist_tail()
{
    int data;
    LinkList head;
    LNode *p,*tail;

    //p = (LNode *)malloc(sizeof(LNode));
    int n = 0;
    printf("请输出节点数值：\n");
    while(1)
    {
        scanf("%d",&data);
        if(data == 0) break;
        p = (LNode *)malloc(sizeof(LNode));
        p->next = NULL;
        p->data = data;
        if(n == 0)
        {
            head = p;
            //tail = p;
            //p->next = NULL;
            //n++;
        }
        else
        {
            //p->data = data;
            tail->next = p;
            //p->next = NULL;
            //tail = p;
            //n++;
        }
        tail = p;
        n++;
    }
    return head;
} 
 
//按序号查找 
LNode *GetElem(LinkList head,int i)
{
    int j = 0;
    LNode *p = head;
    while(p->next&&j<i)
    {
        p = p->next;
        j++;
    }
    if(i == j) return p;
    else return NULL;
}
 
//在序号为x的数之前插入 
void InsertNode(LinkList head,int x,int e)
{
    LNode *p,*q;
    p = GetElem(head,x-1);
    
    //检验找到的节点
    if(p == NULL)
    {
        puts("position error");
        return;
    }
    q = (LNode *)malloc(sizeof(LNode));
    q->data = e;

    q->next = p->next;
    p->next = q;
}
 
//删除 
void DeletNode(LinkList head,int x)
{
    LNode *p,*q;
    p = GetElem(head,x-1);
    q = p->next;
    p->next = p->next->next;
    free(q);
}
 
//修改 
void ChangeNode(LinkList head,int x,int e)
{
    LNode *p;
    p = GetElem(head,x);
    p->data = e;
}
 
//遍历
void bianli(LinkList head)
{
    LNode *h = head;
    while(h!=NULL)
    {
        printf("%d ",h->data);
        h = h->next;
    }
    puts("");
}
 
LinkList sort(LinkList head1,LinkList head2,LinkList head3)
//void sort(LinkList head1,LinkList head2,LinkList head3)
{
    LNode *p1,*p2,*p3;
    p1 = head1; p2 = head2;
    p3 = head3;
    
    while(p1&&p2)
    {
        if(p1->data<=p2->data)
        {
            if(p3 == NULL)
               head3 = p1;
            else
               p3->next = p1;
            p3 = p1;
            p1 = p1->next;
        }
        else
        {
            if(p3 == NULL)
               head3 = p2;
            else
               p3->next = p2;
            p3 = p2;
            p2 = p2->next;
        }
    }
    p3->next = p1?p1:p2;
    //free(head2);
    return head3;
}
 
int main()
{
    LinkList head = creatlist_tail();
    printf("当前链表1所有节点：\n");
    bianli(head);

    printf("查找序号为0的节点：\n");
    LNode *p = GetElem(head,0);
    printf("%d",p->data);
    puts("");
    
    printf("在序号为2的节点前插入数值为7的节点：\n");
    InsertNode(head,2,7);
    bianli(head);

    printf("删除当前序号为2的节点：\n");
    DeletNode(head,2);
    bianli(head);
    
    printf("将序号为0的节点值改为3：\n");
    ChangeNode(head,0,3);
    bianli(head);

    LinkList head2 = creatlist_tail();
    printf("当前链表2所有节点：\n");
    bianli(head2);
    
    LinkList head3 = NULL;
    head3 = sort(head,head2,head3);

    bianli(head3);
    puts("********************");
    LNode *p3 = GetElem(head3,0);
    printf("%d",p3->data);
    puts("");
    return 0;
}