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我有一个使用 ungetc 和 fefo 函数的代码，但我注意到 fefo 没有检查 EOF 下面是我的代码

 #include<stdio.h>
 int main ()
{
 FILE *fp;
  int c;
 char buffer [200];

 fp = fopen("", "r");
 if( fp == NULL ) 
 {
  perror("Error in opening file");
  return(-1);
  }
 while(!feof(fp)) 
 {
   c = getc (fp);
  if(c==EOF) // **why i need to check for EOF if fefo does?**
   break;
   /* replace ! with + */
   if( c == '!' ) 
   {
     ungetc ('@', fp);
   }
   else 
   {
     ungetc(c, fp);
   }
   fgets(buffer, 255, fp);
   fputs(buffer, stdout);
  }
  return(0);
}

输入是：

   hello !world

如果没有明确检查 EOF，则输出

     hello @world
     hello @world // Bad its repeat

显式检查 EOF 时输出

   hello @world // Good

为什么我需要检查 EOF 并在 fefo 时中断？

4

1 回答 1

2

如果我理解正确，您是从文件读取到缓冲区并在它发生时'@'替换它。上面的每一条评论都为您提供了为什么在循环中读取字符并使用测试是不好'!'的原因和链接。whilefeof

将注释放在一起，并稍微清理一下逻辑，下面显示了完成此任务的标准方法。我已将您的代码内联注释以使更改更加明显。如果您有任何问题，请查看并发表评论：

#include <stdio.h>

#define MAXC 255

int main (int argc, char **argv) {

    FILE *fp = NULL;
    int c;
    char input[MAXC];
    char buffer[MAXC];
    size_t idx = 0;

    if (argc < 2) {
        fprintf (stderr, "\n error: insufficient input, filename required.\n");
        return 1;
    }

    if (!(fp = fopen (argv[1], "r")))  {
        fprintf (stderr, "\n error: file open failed '%s' (%p)\n", argv[1], fp);
        return 1;
    }

    while ( (c = getc (fp)) != EOF ) 
    {
        input[idx] = c;

        if (c == '!') c = '@';
        buffer[idx++] = c;

        if (idx == MAXC) {  /* normally realloc if buffer is allocated */
            printf (" warning: maximum size of buffer reached  (%d char)\n", MAXC);
            break;
        }
        // {
        //     ungetc ('@', fp);
        // } else {
        //     ungetc (c, fp);
        // }
        // fgets (buffer, 255, fp);
        // fputs (buffer, stdout);
    }
    fclose (fp);

    input[idx] = buffer[idx] = 0;
    // fputs (buffer, stdout);

    printf ("\n characters in input & buffer are:\n\n");
    printf ("\n  original : %s\n  modified : %s\n\n", input, buffer);

    return 0;
}

输出

$ ./bin/whyfeofbad dat/qbfox2.txt

 characters in input & buffer are:


  original : The quick! brown fox jumps over the lazy! dog. He never says "Hi!", he just saunters up and jumps!

  modified : The quick@ brown fox jumps over the lazy@ dog. He never says "Hi@", he just saunters up and jumps@
于 2015-08-16T08:03:40.137 回答