In C, and many other languages, the file stream error state is saved after each operation, so you can skip error checking on every output line and only do

  if (fflush(stdout) != 0 || ferror(stdout) != 0)
  {
    perror("stdout");
    return EXIT_FAILURE;
  }

at the end of the program. The same should be done for stderr as well.

In GNU programs you can use atexit(close_stdout) to do this automatically.