使用下面的插入函数向单链表插入数据时报错，报错提示为Thread 1: EXC_BAD_ACCESS (code=2, address=0x10000000a)报错的地方是insert函数的 p->next = s;部分，环境为xcode，使用c语言。
enum Status List_Insert(SqListPtr L,int pos,ElemType elem)
{
    enum Status status = fail;
    Ptr p,s;
    p = (Ptr)malloc(sizeof(Node));
    status =List_Retrieve(L,pos-1,&p);
   
    if (status==success) {
        s = (Ptr)malloc(sizeof(Node));

            s->elem = elem;
            s->next = p->next;
            p->next = s;
            status = success;
           
    }else status = range_error;
        
    return status;
}
链表的头文件定义为
typedef int ElemType;

typedef enum Status
{
    success = 1, fail = 0, fatal = -1, range_error = -2
}Status;


typedef struct Node
{
    ElemType elem;
    struct Node *next;
}Node, *Ptr,**SqListPtr;
其余相关函数为
enum Status List_Init(SqListPtr L)
{
    Status s = fail;
    Ptr p;
    if (*L==NULL)
    {
        p = (Ptr)malloc(sizeof(Node));
        if (p == NULL) return s;
        *L = p;
        (*L)->next = NULL;
        s = success;
    }
    return s;
     
}


enum Status List_Create(SqListPtr L,ElemType Data[],int Len)
{
    enum Status s;
    Ptr p;
    s = List_Init(L);
    if (s == success) {
        for (int i = Len-1;i>=0 ;--i ) {
            p = (Ptr)malloc(sizeof(Node));
            if (p) {
                p->elem = Data[i];
                p->next = (*L)->next;
                (*L)->next = p;
            }
            else{
                s = fail;
                break;
            }
        }
    }
    return s;
}


void List_Print(SqListPtr L)
{
   
    Ptr p = *L;
    while(p->next) {
        p = p->next;
        printf("%d\n",p->elem);
    }

}


enum Status List_Retrieve(SqListPtr L,int pos,ElemType *elem)
{
    enum Status s = range_error;
    Ptr p = (*L)->next;
    int i = 1;
    while ( p && i<pos) {
        i++;
        p=p->next;
    }
    if (p&&i==pos) {
        *elem = p->elem;
        s = success;
    }
    return s;
}
int main() {
 
    SqListPtr L = (SqListPtr)malloc(sizeof(Node));
   
    int len = 5;
   
    int Data[] = {1,2,3,4};
   
    List_Create(L, Data, len);
   
    int delepos = 3;
    List_Insert(L,delepos,23);

    return 0;
}