C语言实现双向链表

这个小代码是我凭自己对指针和链表的理解和认识，自己实现的，没有参考其他人的代码，如果有相同的地方，那真的只是巧合，代码我在ubuntu 15.04下测试通过，可能存在很多错误和漏洞．

doublelist.c

/*************************************************************************
  > File Name: doublelist.c
  > Author: ChenYiLiang
  > Mail: chenyiliangex@163.com 
  > Created Time: Sat 21 Mar 2015 07:32:22 PM CST
 ************************************************************************/
 
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
 
struct userdata{
  int userid;
  char username[30];
 
  struct userdata *previous;
  struct userdata *next;
};
 
 
 
struct userdata *header;
size_t scanf_id;
char scanf_name[30];
 
int yesno;
int deletePosition;
int alterPosition;
int alterId;
char alterName[30];
 
int searchPosition;
 
FILE *ptr_fpid;
 
/*向链表中插入数据*/
int insert_list(struct userdata *header, size_t position, char name[], size_t id);
/*删除链表中指定的节点*/
int delete_node(struct userdata *header, size_t position);
/*修改指定位置的节点信息*/
int alter_node(struct userdata *header, size_t position, size_t id, char name[]);
/*查找链表中的数据*/
struct userdata *search_node(struct userdata *header, size_t position);
/*遍历链表*/
int travel_list(struct userdata *header);
/*判断链表是空*/
int isempty(struct userdata *header);
 
/*将链表结构写入文件*/
int write_into_file(struct userdata *header, FILE *fp);
/*从文件读取数据放到链表中*/
int read_from_file(struct userdata *header, FILE *fp);
 
int main(){
  struct userdata *header_node = (struct userdata *)malloc(sizeof(struct userdata));
  header_node -> previous = NULL;
  header_node -> next = NULL;
 
  read_from_file(header_node, ptr_fpid);
  travel_list(header_node);
  while(1){
  //scanf("%*[^\n]");
  //scanf("%*c");
  //scanf("%*[^\n]");
  printf("please input id - ");
  scanf("%d", &scanf_id);
  //scanf("%*c");
  //scanf("%*[^\n]");
  printf("please input your name - ");
  scanf("%s", scanf_name);
 
  printf("%d - %s\n\n", scanf_id, scanf_name);
 
  //isempty(header_node);
 
  /*0表示默认插入到链表的尾部*/
  insert_list(header_node, 0, scanf_name, scanf_id);
   
  //write_into_file(header_node, ptr_fpid);
  //isempty(header_node);
 
 
    printf("input anymore - ");
    scanf("%d", &yesno);
    if(yesno == -1){
      break;
    }
 
  scanf("%*c");
  scanf("%*[^\n]");
// travel_list(header_node);
 
  }
  getchar();
  //printf("delete position data - ");
  //scanf("%d", &deletePosition);
  //delete_node(header_node, deletePosition);
 
// printf("alter data for position - ");
// scanf("%d", &alterPosition);
// printf("please inout new id - ");
// scanf("%d",&alterId);
// printf("please input new name - ");
// scanf("%s", alterName);
// alter_node(header_node, alterPosition, alterId, alterName);
  write_into_file(header_node, ptr_fpid);
  travel_list(header_node);
  printf("\n\n");
  printf("please input position to search - ");
  scanf("%d", &searchPosition);
  struct userdata *searchData = search_node(header_node, searchPosition);
  printf("%d\n", searchData -> userid);
  printf("%s\n", searchData -> username);
  return 0;
}
 
/* 插入节点 */
int insert_list(struct userdata *header, size_t position, char name[], size_t id ){
  struct userdata *temp_newuser = header;
  struct userdata *getMemory = (struct userdata *)malloc(sizeof(struct userdata));
 
  getMemory -> userid = id;
  strncpy(getMemory -> username, name, 30);
  /*当position == 0时,表示默认插入到链表的尾部*/
  if(0 == position){
    if(NULL != temp_newuser -> next){
      while(NULL != temp_newuser -> next){
        temp_newuser = temp_newuser -> next;
      }
    }
  }
 
  /*当position > 1时则寻找合适的位置插入*/
  if(1 <= position){
    for(int i = 0; i <= position; i++){
      /*当执行此处的代码时表示,链表已经到达尾部或者是空链表*/
      if(NULL == temp_newuser -> next){
        break;
      }
      temp_newuser = temp_newuser -> next;
    }
  }
 
  getMemory -> previous = temp_newuser;
  if(temp_newuser -> next == NULL){
    temp_newuser -> next = getMemory;
    getMemory -> next = NULL; 
  }else{
    temp_newuser -> next -> previous = getMemory;
    getMemory -> next = temp_newuser -> next;
    temp_newuser -> next = getMemory;
  }
 
  return 0;
}
 
/*删除链表中指定的节点*/
int delete_node(struct userdata *header, size_t position){
  int is_empty = isempty(header);
  if(0 == is_empty){
    printf("this si a empty list!\n\n");
    return -1;
  }
 
  struct userdata *deleteNode = header;
 
    for(int i = 0; i < position; i++ ){
      /*当执行此处的代码时表示,链表已经到达尾部或者是空链表*/
      if(NULL == deleteNode -> next){
        break;
      }
      deleteNode = deleteNode -> next;
    }
 
  /**/
  deleteNode -> next -> previous = deleteNode -> previous;
  deleteNode -> previous -> next = deleteNode -> next;
  free(deleteNode);
 
  return 0;  
}
 
/*修改指定位置的节点信息*/
int alter_node(struct userdata *header, size_t position, size_t id, char name[]){
  int isEmpty = isempty(header);
  if(0 == isEmpty){
    printf("this is a empty list\n\n");
    return -1;
  }
   
  struct userdata *alterNode = header; 
    for(int i = 0; i < position; i++ ){
      /*当执行此处的代码时表示,链表已经到达尾部或者是空链表*/
      if(NULL == alterNode -> next){
        break;
      }
      alterNode = alterNode -> next;
    }
 
    alterNode -> userid = id;
    strncpy(alterNode -> username, name, 30);
 
  return 0;
}
 
/*查找链表中的数据*/
struct userdata *search_node(struct userdata *header, size_t position){
  int isEmpty = isempty(header); 
  if(0 == isEmpty){
    printf("this is a empty!\n");
    return NULL;
  }
 
  struct userdata *searchNode = header;
  for(int i = 0; i < position; i++){
    if(NULL == searchNode -> next){
      break;
    }
    searchNode = searchNode -> next;
  }
 
  return searchNode;
}
 
/*遍历链表*/
int travel_list(struct userdata *header){
  struct userdata *travel = header;
  if(NULL == travel -> next){
    printf("This is a empty list!!\n");
    return 1;
  }
   
  for(travel = travel -> next ; ; travel = travel -> next){
    printf("%d\n",travel -> userid);
    printf("%s\n", travel -> username);
    if(NULL == travel -> next){
      break;
    }
  }  
 
  return 1;
}
 
/*判断链表是空*/
int isempty(struct userdata *header){
  if(header -> next == NULL){
    return 0;
  }else{
    return 1;
  }
}
 
/*将链表结构写入文件*/
int write_into_file(struct userdata *header, FILE *fp){
  fp = fopen("listdata", "wb");
  if(NULL == fp){
    perror("open file failed when write into file!"),exit(-1);
  }
 
  printf("come into write!\n");
  for(struct userdata *move = header -> next; ; move = move -> next){
    fwrite(move,sizeof(struct userdata), 1, fp);
    if(NULL == move -> next){
      break;
    }
  }
  fclose(fp);
  fp = NULL;
  return 0;
}
/*从文件读取数据放到链表中*/
int read_from_file(struct userdata *header, FILE *fp){
  struct userdata *readfile = header;
  fp = fopen("listdata", "rb");
  if(NULL == fp){
    perror("open file failed when read - ");
    return -1;
  }
 
  while(1){
    struct userdata *newread = (struct userdata *)malloc(sizeof(struct userdata));
    fread(newread, sizeof(struct userdata), 1, fp);
    if(feof(fp)){/*当读取到文件的尾部时．跳出循环*/
      break;
    }
    readfile -> next = newread;
    newread -> next = NULL;
    newread -> previous = readfile;
    readfile = newread;
  }
  fclose(fp);
  fp = NULL;
  return 0;
}