C Program reliant on fputs to reach conditional

I have the following snippet of a C program:

  char line[128];
  int io;
  FILE *fp = fopen("/proc/diskstats", "r");

   while(fgets(line, sizeof line, fp)) {
       fputs(line, stdout);
       if(dev_t_conversion(line) == get_file_devid("/")) {
            sscanf(line, "%*d\t%d", &io);
            printf("%d\n", io);
            fclose(fp);
        }
    }

If I remove the fputs(line, stdout); line, the if conditional is never reached. I cannot understand why that is. Why do I need to put line to stdout?