code: public static function convertEncoding($str, $to, $from=null)
  	{
  		if ($str == '')
  		{
  			return '';
  		}
  
  		if (!$from)
  		{
  			$from = mb_detect_encoding($str, 'ASCII,ISO-2022-JP,UTF-8,EUC-JP,ISO-8859-1');
  		}
  
  		if ($from == $to)
  		{
  			return $str;
  		}
  
  		if ($from == 'UTF-8' && $to == 'ISO-8859-1')
  		{
  			return utf8_decode($str);
  		}
  
  		if ($from == 'ISO-8859-1' && $to == 'UTF-8')
  		{
  			return utf8_encode($str);
  		}
  
  		return mb_convert_encoding($str, $to, $from);
  	}
docs: Convert the character encoding
  
  @param string $str  The input string
  @param string $to   The target character set
  @param string $from An optional source character set
  
  @return string The converted string