c - 从文件读取结构到终端，段错误

Question

我正在尝试从具有相似行的文本文件中读取(大约 200 行不时有一些空行)。我知道有些东西可以未初始化，但我对它是什么一无所知。我现在想做的只是从文件中读取并将其打印到终端窗口。

我真的希望你能帮助我!谢谢。

几行文本文件的例子:

Fre     19/07 18.30     AGF - FCM      0 - 2     9.364   
Lor     20/07 17.00     VFF - RFC      2 - 2     4.771   
Son     21/07 14.00     OB - SDR       1 - 1     7.114   

我的结构看起来像这样:

struct match {
    char weekday[MAX_NAME_LEN];
    int day;
    int month;
    int hours;
    int minutes;
    char home_team[MAX_NAME_LEN];
    char away_team[MAX_NAME_LEN];
    int home_team_goals;
    int away_team_goals;
    int spectators_thds;
    int spectators_hdrs;
};

我的 read_file 函数如下所示:

void read_file(struct match *match) {
    FILE *fp;
    int i;
    fp = fopen("superliga-2013-2014", "r"); 
    while (!fp) {
        error("Cannot open file.");
    }

    struct match *matches = (struct match *) malloc(sizeof(match) * MAX_MATCHES);
    while(!feof(fp)) {
        fscanf(fp, " %s %i/%i %i.%i %s - %s %i - %i %i.%i \n", 
               matches[i].weekday, &matches[i].day, &matches[i].month, &matches[i].hours,
               &matches[i].minutes, matches[i].home_team, matches[i].away_team,
               &matches[i].home_team_goals, &matches[i].away_team_goals,
               &matches[i].spectators_thds, &matches[i].spectators_hdrs);
    }
    fclose(fp);
    free(fp);
}

我的 main 函数如下所示:

int main(int argc, char *argv[]) {
    int i;
    struct match *matches;
    void read_file(struct match *matches);
    for (i = 0; i < MAX_MATCHES; ++i) {
        printf(" %s %i/%i %i.%i %s - %s %i - %i %i.%i ",
               matches[i].weekday, matches[i].day, matches[i].month, matches[i].hours,
               matches[i].minutes, matches[i].home_team, matches[i].away_team,
               matches[i].home_team_goals, matches[i].away_team_goals,
               matches[i].spectators_thds, matches[i].spectators_hdrs);
    }

    return 0;
}

编译没有问题，但是当我尝试运行它时出现Segmentation fault。然后我使用 Valgrind，它给了我这条消息:

==12799== Use of uninitialised value of size 8
==12799==    at 0x4007B8: main (in /home/dradee/Dropbox/UNI/Programmering/C/readfile)
==12799== 
==12799== Invalid read of size 4
==12799==    at 0x4007B8: main (in /home/dradee/Dropbox/UNI/Programmering/C/readfile)
==12799==  Address 0x34 is not stack'd, malloc'd or (recently) free'd
==12799== 
==12799== 
==12799== Process terminating with default action of signal 11 (SIGSEGV)
==12799==  Access not within mapped region at address 0x34
==12799==    at 0x4007B8: main (in /home/dradee/Dropbox/UNI/Programmering/C/readfile)

Answer 1

1. Don't转换 malloc()

   struct match *matches = (struct match *) malloc(sizeof(match) * MAX_MATCHES);
   

   更好的是

   struct match *matches = malloc(sizeof(struct match) * MAX_MATCHES);
   

2. 检查malloc()的结果，失败返回NULL。

3. 不要检查 !feof() 因为它是 always wrong , 所以改变这个

   while(!feof(fp))
   

   与

   while (fscanf(fp, " %s %i/%i %i.%i %s - %s %i - %i %i.%i \n", 
          matches[i].weekday, &matches[i].day, &matches[i].month, &matches[i].hours,
          &matches[i].minutes, matches[i].home_team, matches[i].away_team,
          &matches[i].home_team_goals, &matches[i].away_team_goals,
          &matches[i].spectators_thds, &matches[i].spectators_hdrs) == 11)
   

4. 这是最重要的:您在 printf() 循环中迭代直到 MAX_MATCHES，当您不这样做时必须阅读 MAX_MATCHES。因此，您需要记录成功读取的项目数，并在第二个 for 循环中使用它。

   例如，您可以将读取的项目数从 read_file 返回到 main，并使用它。

   您在 read_file() 中已有一个计数器，但请阅读下一点。

5. 您永远不会在 read_file() 的 while 循环中递增 i。

6. 这很奇怪

   void read_file(struct match *matches);
   

   你是说

   read_file(matches);
   

7. 这是不正确的

   free(fp);
   

   您已经执行了fclose(fp)，这是释放FILE * 资源的正确方法，那里的free()将导致未定义的行为，这可能是段错误或其他任何事情，因为它是未定义的。

8. 这没有意义

   while (!fp) { ... }
   

   你的意思是

   if (!fp) { ... }
   

9. 您的read_file() 函数仅在本地分配结构，然后您无法从main() 访问它们，你能做的就是这个

   int read_file(struct match **matches)
   {
       FILE         *fp;
       int           i;
       struct match *match;        
       if (matches == NULL)
           return 0;
       *matches = NULL;
       fp       = fopen("superliga-2013-2014", "r");
       if (!fp)
       {
           error("Cannot open file.");
           return 0;
       }        
       match = malloc(sizeof(struct match) * MAX_MATCHES);
       if (match == NULL)
           return 0;
       while ((fscanf(fp, " %s %i/%i %i.%i %s - %s %i - %i %i.%i \n",
                  match[i].weekday, &match[i].day, &match[i].month, &match[i].hours,
                  &match[i].minutes, match[i].home_team, match[i].away_team,
                  &match[i].home_team_goals, &match[i].away_team_goals,
                  &match[i].spectators_thds, &match[i].spectators_hdrs) == 11) && (i < MAX_MATCHES))
       {
           i++;
       }
       fclose(fp);
   
       *matches = match;
       return i;
   }
   

   然后是你的 main()

   int main(int argc, char *argv[]) 
   {
       int           i;
       struct match *matches;
       int           count;
       count = read_file(&matches);
       for (i = 0 ; i < MAX_count ; ++i) 
       {
           printf(" %s %i/%i %i.%i %s - %s %i - %i %i.%i ",
                  matches[i].weekday, matches[i].day, matches[i].month, matches[i].hours,
                  matches[i].minutes, matches[i].home_team, matches[i].away_team,
                  matches[i].home_team_goals, matches[i].away_team_goals,
                  matches[i].spectators_thds, matches[i].spectators_hdrs);
       }
       free(matches);        
       return 0;
   }