Question

我目前正在第一次学习C，而且我需要创建一个链接列表。我在过去没有遇到过简单的问题，但功能性抽象和指针传递似乎让我感到困惑，因为我无法理解这一点。运行程序时，我一直收到分段错误。基本上我正在从2个单独的文件中读取数据，然后填充列表。从那里我做了另外的数据，但在这个阶段它是无关紧要的，因为我甚至无法从文件加载数据。使用从主函数传递给各种函数的tm结构来控制列表。

我一直在使用Valgrind和gdb来尝试和诊断，但是对于调试来说，新手很难。经过两天的反复试验，我觉得我有一些重要的事情。这是我的代码和错误消息：

/* global type definitions */
typedef struct tm * tm_type_ptr;
typedef struct stock_list * stock_list_ptr;
typedef struct coin * coin_list_ptr;
typedef struct tm {
   coin_list_ptr coins;
   stock_list_ptr stock;
} tm_type;

/*coin structs*/
enum coin_types {
   FIVE_CENTS=5,
   TEN_CENTS=10,
   TWENTY_CENTS=20,
   FIFTY_CENTS=50,
   ONE_DOLLAR=100,
TWO_DOLLARS=200
};

struct coin {
   enum coin_types denomination;
   unsigned count;
};

/* stock structs*/
struct stock_data 
{
   char ticket_name[TICKET_NAME_LEN+1];
   char ticket_type;
   char ticket_zone[TICKET_ZONE_LEN+1];
   unsigned int ticket_price;
   unsigned int stock_level;
};

typedef struct stock_node 
{
   struct stock_data * data;
   struct stock_node * next_node;
} stock_node;

struct stock_list
{
   stock_node * head_stock;
   unsigned int num_stock_items;
};

然后填充结构我使用以下函数：

BOOLEAN system_init(tm_type * tm)
{

  tm->coins=malloc(sizeof(struct coin) * NUM_COINS);
  tm->stock=malloc(sizeof(struct stock_list));
  tm->stock->head_stock = malloc(sizeof(stock_node));
  tm->stock->head_stock->data = malloc(sizeof (struct stock_data));
  tm->coins->count = 0;
  tm->stock->num_stock_items =0;
  if (tm == NULL)
  {
     return FALSE;
  }
  else
  {
     return TRUE;
  } 
}

BOOLEAN load_data(tm_type * tm, char * stockfile, char * coinsfile)
{
  FILE *stock_fp = fopen(stockfile, "r");
  FILE *coins_fp = fopen(coinsfile, "r");
  char *input= NULL, *token = NULL;
  unsigned coin_type, amount;
  /*stock variables*/
  unsigned stock_count=0;
  unsigned int ticket_price, stock_level;

  char *ticket_name = NULL, ticket_type, *ticket_zone= NULL;
     while(fgets(input, buffer_size, coins_fp) != NULL)
     {
        token= strtok(input, ",");
        coin_type = strtol(token, NULL, 10);
        if(token != NULL)
        {
           token= strtok(NULL, ",");
           amount = strtol(token, NULL, 10);
        }

        if(!populate_coin_array(tm, coin_type, amount))
        {
           printf("OMG YOU SUCK!\n");
        } 
     }   
  } 
  /*display_coin_array(tm); */   
 }
 fclose(coins_fp);
 free(input);
 /*read stock file and populate stock structure */
 if(fseek(stock_fp ,0, SEEK_END) == 0)
 {
  long buffer_size = ftell(stock_fp);
  if(buffer_size == -1)
  {
     printf("Error! Exiting!\n");
     return FALSE;
  }
  input = malloc(sizeof(char) * (buffer_size+1));  /*allocate buffer size plus one for      `     '\0'*/

  if(fseek(stock_fp,0,SEEK_SET) == 0)
  {
     while(fgets(input, buffer_size, stock_fp) != NULL)
     {
        ticket_name = strtok(input, ",");
        ticket_type = *(strtok(NULL, ","));
        ticket_zone = strtok(NULL, ",");
        token = strtok(NULL, ",");
        ticket_price = strtol(token, NULL, 10);
        token = strtok(NULL,",");
        stock_level = strtol(token, NULL, 10);
        stock_count++;
        if(!populate_stock_list(tm, ticket_name, ticket_type, ticket_zone, 
        ticket_price, stock_level, stock_count))
        {
           printf("ERROR!!!\n");
        } 

     }    

  } 
  display_stock_list(tm, stock_count);  
}
fclose(stock_fp);
free(input);
return TRUE;
}

BOOLEAN populate_coin_array(tm_type *tm, unsigned coin_type, unsigned amount)
{
  struct coin single_coin;
  struct coin *coin_array;
  coin_array = malloc(sizeof(struct coin) * NUM_COINS);
  single_coin = *(tm->coins);
  single_coin.denomination = coin_type;
  single_coin.count = amount;
  *coin_array = single_coin;
  tm->coins = coin_array;
  return TRUE;
}

BOOLEAN populate_stock_list(tm_type *tm, char  *ticket_name, char ticket_type,
char *ticket_zone, unsigned int ticket_price, unsigned int stock_level, 
unsigned int stock_count)
{
   tm_type temp_list;
   struct stock_node *new_node;
   temp_list = *tm;
   new_node = malloc(sizeof(stock_node*));
   if(new_node != NULL)
   {
      strcpy(new_node->data->ticket_name, ticket_name);
      new_node->data->ticket_type = ticket_type;
      strcpy(new_node->data->ticket_zone , ticket_zone);
      new_node->data->ticket_price = ticket_price;
      new_node->data->stock_level = stock_level;
      new_node->next_node = temp_list.stock->head_stock;
      temp_list.stock->head_stock = new_node;
      temp_list.stock->num_stock_items = stock_count;
   }
   return TRUE;
 }

我很抱歉大量的乱码，我从一些.c和.h文件中取出它。我试图尽可能地削减它以便更容易进行故障排除。

Valgrind正在给我这个：

==16716== Use of uninitialised value of size 8
==16716==    at 0x4C2BFFC: strcpy (in /usr/lib/valgrind/vgpreload_memcheck-amd64- 
linux.so)
==16716==    by 0x400D37: populate_stock_list (tm_stock.c:37)
==16716==    by 0x40128F: load_data (tm_utility.c:129)
==16716==    by 0x40098F: main (tm.c:57)
==16716== 
==16716== Invalid write of size 1
==16716==    at 0x4C2BFFC: strcpy (in /usr/lib/valgrind/vgpreload_memcheck-amd64-
linux.so)
==16716==    by 0x400D37: populate_stock_list (tm_stock.c:37)
==16716==    by 0x40128F: load_data (tm_utility.c:129)
==16716==    by 0x40098F: main (tm.c:57)
==16716==  Address 0x0 is not stack'd, malloc'd or (recently) free'd
==16716== 
==16716== 
==16716== Process terminating with default action of signal 11 (SIGSEGV)
==16716==  Access not within mapped region at address 0x0
==16716==    at 0x4C2BFFC: strcpy (in /usr/lib/valgrind/vgpreload_memcheck-amd64-
linux.so)
==16716==    by 0x400D37: populate_stock_list (tm_stock.c:37)
==16716==    by 0x40128F: load_data (tm_utility.c:129)
==16716==    by 0x40098F: main (tm.c:57)

可以帮我指出正确的方向吗？我不希望有人给我答案，我只想知道为什么会这样。

谢谢！

Answer 1

在使用之前，您需要为new_node->data分配struct stock_data *。此外，在malloc()传递结构大小中，您分配的不是其指针的大小。

更新将是

//--------------------------------v no * here
new_node = malloc(sizeof(*new_node));
if(new_node != NULL)
{
    new_node->data = malloc(sizeof(*(new_node->data)));
    ...
    //your code

Segmentation Fault尝试创建链表

1 个答案: