fseek() 越过文件限制但不终止

Question

在最后一个 while 循环中，应该打印文件中存储的每第 5 个字符，但循环无限期地进行并且不会终止。 feof() 函数在到达 END OF FILE 时应该 return 1 并且应该退出循环但循环将无限期地进行。

#include<stdio.h>

main() {
  long n, k;
  char c;
  FILE *fp;
  fp = fopen("RANDOM", "w");

  while ((c = getchar()) != EOF) {
    putc(c, fp);
  }

  n = ftell(fp);
  printf("\nNo. of characters entered by the user is : %ld\n", n);
  fclose(fp);
  fp = fopen("RANDOM", "r");

  while(feof(fp) == 0) {
    n = ftell(fp);
    c = getc(fp);
    printf("The character at %ld position is %c\n", n, c);
    fseek(fp, 4l, 1);
  }
}

Answer 1

来自man fseek()：

A successful call to the fseek() function clears the end-of-file indicator for the stream.

和fseek()即使将位置指示器设置在EOF 之后也会成功。因此很明显，当 fseek() 是循环中的最后一个命令时，while (feof(fp) == 0) 将永远不会终止。

相反，您可以这样做：

for( ;; ) {
    n = ftell(fp);
    if( (c = getc(fp)) == EOF )
         break;
    printf("The character at %ld position is %c\n", n, c);
    fseek(fp, 4l, SEEK_CUR);
}

fseek() 越过文件限制但不终止

fseek() crossing file limit and not terminating

c

fseek