C Primer Plus（第六版）中文版 中的错误1

 #include<stdio.h>
 #include<stdlib.h>
 #include<string.h>
 #define TSIZE 45

 struct film {
     char title[TSIZE];
     int rating;
     struct film *next;
 };
 char * s_gets(char * st, int n);

 int main(void)
 {
     struct film * head = NULL;
     struct film * prev;
     struct film * current;
     char input[TSIZE];

     puts("Enter first movie title:");
     while(s_gets(input, TSIZE) != NULL && input[] != '\0')
     {
         current = (struct film *) malloc(sizeof(struct film));
         if(head == NULL)
             head = current;
         else
             prev->next = current;
         current->next = NULL;
         strcpy(current->title, input);
         puts("Enter your rating <0-10>:");
         scanf("%d", &current->rating);
         while(getchar() != '\n')
             continue;
         puts("Enter next movie title (empty line to stop):");
         prev = current;
     }

     if(head == NULL)
         printf("No data entered. ");
     else
         printf("Here is the movie list:\n");
     current = head;
     while(current != NULL)
     {
         printf("Movie: %s Rating: %d\n",
                current->title, current->rating);
         current = current->next;
     }

     current = head;
     while(current != NULL)
     {
         current = head;
         head = current->next;
         free(current);
     }
     printf("Bye!\n");

     return ;
 }

 char * s_gets(char * st, int n)
 {
     char * ret_val;
     char * find;

     ret_val = fgets(st, n, stdin);
     if(ret_val)
     {
         find = strchr(st, '\n');
         if(find)
             *find = '\0';
         else
             while(getchar() != '\n')
                 continue;
     }

     return ret_val;
 }

上面的代码来自《C Primer Plus》（第六版）中文版，第573-574页。

其中代码的第51行有错误。

不知道这个错误是印刷有错，还是原书有错。在此指出。

改正代码：

是将第51行的while（current != NULL）改为

while (head != NULL)就可以了。

原因如下：

将第51-56行代码之间添加一些输出，代码如下：

     while(current != NULL)
     {
         printf("current1 = %p\n", current);
         printf("head1 = %p\n\n",head);
         current = head;
         printf("current2 = %p\n", current);
         printf("head2 = %p\n\n",head);
         head = current->next;
         printf("current3 = %p\n", current);
         printf("head3 = %p\n\n",head);
         free(current);
         printf("current4 = %p\n", current);
         printf("head4 = %p\n\n",head);
     }

输出结果如下：

从上面的输出结果可以看出，最后一个head2指针已经是00000000了，是一个指向未知地址的指针。所以再次释放一个current就会出错。

改正后的输出：