Take the lead in the bidirectional circular linked list (variable-length structure)

//Take the lead in the bidirectional circular linked list (variable-length structure)

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include "list.h"

#define NAMESIZE 24

typedef struct stuinfo{
 int id;
 char name[NAMESIZE];
 int math;
}DATA;

static void print_s(const void *data) // data 接收地址是p->data
{
 const DATA *stup = data;   // 把接受到的数据放置到结构体中。
 printf("%d %s %d\n",
   stup->id,
   stup->name,
   stup->math);
}

static int IdCmp(const void *key, const void *data)
{
 const int *id = key;
 const DATA *stup = data;

 return (*id - stup->id);
}
static int NameCmp(const void *key, const void *data)
{
 const char *name = key;
 const DATA *stup = data;

 return strcmp(name, stup->name);
}

int main()
{
 int i;
 int id = 5;
 char name[NAMESIZE] = "stu3";
 DATA stu, *stup;
 LIST handle = NULL;

 handle = ListCreate(sizeof(DATA));  //handle为头节点的指针，头节点数据域大小为DATA的类型大小。
 if(NULL == handle)
  return -1;

 for(i = 0; i < 6; i++)
 {
  stu.id = i + 1;
  snprintf(stu.name,NAMESIZE,
    "stu%d", i + 1); // int snprintf(char *str, size_t size, const char *format, ...);
  stu.math = 100 - i;

  //ListInsert(handle, &stu, HEADINSERT);
  ListInsert(handle, &stu, TAILINSERT);
 }
 /*find*/
 //stup = ListFind(handle, &id, IdCmp);
 stup = ListFind(handle, name, NameCmp);
 if(stup != NULL)
  print_s(stup);
 else
  printf("not find\n");
 ListDelete(handle, name, NameCmp);
 ListDelete(handle, &id, IdCmp);

 ListDisplay(handle, print_s);
 ListDispose(handle);
 
 return 0;
}
----------------------------------------------#ifndef _LIST_H__
#define _LIST_H__

#define HEADINSERT 1
#define TAILINSERT  2

struct listnode;
struct headnode;
typedef struct headnode *LIST;
typedef struct listnode *PtrNode;

typedef void print(const void *);
typedef int cmp(const void *, const void *);

LIST ListCreate(int);
int ListInsert(LIST, const void *, int);
void *ListFind(LIST, const void *, cmp *);
int ListDelete(LIST, const void *, cmp *);
int ListFetch(LIST, const void *, cmp *, void *);
void ListDisplay(LIST, print *);
void ListDispose(LIST);

struct listnode{
 struct listnode *prev;
 struct listnode *next;
 char data[0];
};

struct headnode{
 int size;
 struct listnode head;
};

#endif
----------------------------------------------------------

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include "list.h"

LIST ListCreate(int size)  //LIST 说明返回值handle是struct node * 类型的
{
 LIST handle = malloc(sizeof(*handle));
 if(NULL == handle)
  return NULL;

 handle->size = size;
 handle->head.next = handle->head.prev = &handle->head;
 return handle;
}

int ListInsert(LIST l, const void *data, int mode)//l 为指向头节点的指针handle,  data类型为const void *类型，要接受DATA类型变量stu的地址。
{
 PtrNode cur = malloc(sizeof(*cur) + l->size); //cur为struct listnode *类型，分配指针域和数据域空间。
 if(NULL == cur)
  return -1;
 
 memcpy(cur->data, data, l->size); //

 if(mode == HEADINSERT) //先连后断
 {
  cur->prev = &l->head;
  cur->next = l->head.next;
 }
 else if(mode == TAILINSERT)
 {
  cur->prev = l->head.prev;
  cur->next = &l->head;
 }
 else
 {
  free(cur);
  return -2;
 }
 cur->next->prev = cur;
 cur->prev->next = cur;
 return 0;
}

//查找数据，id或name,通过调用main中的IdCmp或NameCmp函数（函数名为函数的地址，所以加*/ cmp * funp） 而cmp表示函数的类型为参数为（const void * ，const void*）返回值为int。
static PtrNode find(LIST l, const void *key, cmp *funp)
{
 PtrNode p = l->head.next;

 for(; p != &l->head && funp(key,p->data); p = p->next);

 return p; //查找返回值为PtrNode 类型
}

void *ListFind(LIST l, const void *key, cmp *funp)  //查找数据
{
 PtrNode p =  find(l, key, funp);
 if(p == &l->head)
  return NULL;
 return p->data; // 返回值为void *类型 //data本身是listnode节点的数据域data[0]的地址，p->data表示地址。
}

int ListDelete(LIST l, const void *key, cmp *funp)
{
 PtrNode p = find(l, key, funp);
 if(p == &l->head)
  return -1;

 p->next->prev = p->prev;
 p->prev->next = p->next;
 free(p);
 return 0;
}
int ListFetch(LIST l, const void *key, cmp *funp, void *data)
{
 PtrNode p = find(l, key, funp);
 if(p == &l->head)
  return -1;

 memcpy(data, p->data, l->size);
 p->next->prev = p->prev;
 p->prev->next = p->next;
 free(p);
 return 0;
}

void ListDisplay(LIST l, print * funp)// print为返回值为void，参数为const void * 类型，函数调传地址，
{
 PtrNode p = l->head.next;// p指向第一个节点

 while(p != &l->head)
 {
  funp(p->data);
  p = p->next;
 }
}

void ListDispose(LIST l)
{
 PtrNode p = l->head.next;
 PtrNode q;

 while(p != &l->head)
 {
  q = p;
  p = p->next;

  free(q);
 }
 free(l);
}