如何使用 feof(FILE *f)？

发布于 2024-10-05 09:32:42 字数 969 浏览 7 评论 0原文

我在 do-while 循环上遇到了困难，它应该停止当我们到达文件末尾时。这是循环代码：

do  {
    if (pcompanyRow[0] != '#' && pass == 1) {
        strtok(pcompanyRow, ":");
        pcompanyName = strcpy(pcompanyName, strtok(NULL, ""));
        pass = 2;
        fgets(pcompanyRow, 1024, f);
    }
    if (pcompanyRow[0] != '#' && pass == 2) {
        strtok(pcompanyRow, ":");
        pcompanySMSPrice = strcpy(pcompanySMSPrice, strtok(NULL , ""));
        pass = 3;
        fgets(pcompanyRow, 1024 , f);
    }
    if (pcompanyRow[0] != '#' && pass == 3) {
        strtok(pcompanyRow, ":");
        pcompanyMMSPrice = strcpy(pcompanyMMSPrice, strtok(NULL, ""));
        pass = 4;
        fgets(pcompanyRow, 1024, f);
    }
    if (pass == 4)  {
        AppendCompanyNode(pcompanyList, pcompanyName, pcompanySMSPrice, pcompanyMMSPrice);
        pass = 1;
    }
} while (!feof(f));

使用调试器运行后，我注意到我遇到的所有崩溃问题都是因为即使它到达整行，它也不会退出此循环。

应该怎样写才能正确呢？

原文

I'm having a hard time with a do-while loop, that is supposed to stop
when we reach the end of the file. Here's the loop code:

do  {
    if (pcompanyRow[0] != '#' && pass == 1) {
        strtok(pcompanyRow, ":");
        pcompanyName = strcpy(pcompanyName, strtok(NULL, ""));
        pass = 2;
        fgets(pcompanyRow, 1024, f);
    }
    if (pcompanyRow[0] != '#' && pass == 2) {
        strtok(pcompanyRow, ":");
        pcompanySMSPrice = strcpy(pcompanySMSPrice, strtok(NULL , ""));
        pass = 3;
        fgets(pcompanyRow, 1024 , f);
    }
    if (pcompanyRow[0] != '#' && pass == 3) {
        strtok(pcompanyRow, ":");
        pcompanyMMSPrice = strcpy(pcompanyMMSPrice, strtok(NULL, ""));
        pass = 4;
        fgets(pcompanyRow, 1024, f);
    }
    if (pass == 4)  {
        AppendCompanyNode(pcompanyList, pcompanyName, pcompanySMSPrice, pcompanyMMSPrice);
        pass = 1;
    }
} while (!feof(f));

After running with the debugger, I noticed that all the crash problems I have are because it doesn't go out of this loop even when it reached the whole lines.

How should I write it correctly?

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⒈起吃苦の倖褔 2024-10-12 09:32:42

永远不应该使用 feof() 作为循环的退出指示符。 feof() 仅在读取文件末尾 (EOF) 后才为 TRUE，而不是在到达 EOF 时为 TRUE

来源在这里。它还详细解释了问题以及如何解决它。

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花辞树 2024-10-12 09:32:42

我会改变你的循环和逻辑来使用它：

while (fgets(pcompanyRow, 1024, f) != NULL) {

    /* do things */

}

当 fgets() 尝试读取文件末尾之后，它将返回 NULL 并且你将跳出循环。您仍然可以继续使用 pass 和其他标志/逻辑，但您检查的条件会略有不同。

I would change your loop and logic to use this:

while (fgets(pcompanyRow, 1024, f) != NULL) {

    /* do things */

}

when fgets() attempts to read past the end of the file, it will return NULL and you'll break out of the loop. You can still continue to use pass and your other flags/logic, but the conditions you check for will be slightly different.

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亂 2024-10-12 09:32:42

我建议同时使用 fgets() 和 feof()。
文件中的最后一个字符串可能有 \n，也可能没有。如果您只使用 feof()，您可以跳过（丢失）最后一行。

 for(;;)
 {char *pc;

  pc=fgets(buf,sizeof(buf),fd);

  if(!pc)
    {//it may be read error or end of file
      if(feof(fd))
        {//it is end of file, normal exit from for
         break;      
        }
       else
        {//it is i/o error 
         fclose(fd);
         return 2;
        }
    }
}//for

I suggest use both fgets() and feof().
Last string in file might have \n or might not. If you use only feof(), you can skip (lost) last line.

 for(;;)
 {char *pc;

  pc=fgets(buf,sizeof(buf),fd);

  if(!pc)
    {//it may be read error or end of file
      if(feof(fd))
        {//it is end of file, normal exit from for
         break;      
        }
       else
        {//it is i/o error 
         fclose(fd);
         return 2;
        }
    }
}//for

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