Warning: fread(): Length parameter must be greater than 0. in /home/test/test.php on line xxxxxx

// ÁöÁ¤µÈ ÆÄÀÏÀÇ ³»¿ëÀ» Àоî¿È
 function test($filename) {
  if(!file_exists($filename)) return '';

  $f = fopen($filename,"r");
==>>  $str = fread($f, filesize($filename));
  fclose($f);
  return $str;
 }
 
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$str = @fread($f, filesize($filename));