var str_trim = "   !hi  !23   !"

str_trim.stringByTrimmingCharactersInSet(NSCharacterSet.whitespaceCharacterSet())//"!hi  !23   !"去掉两边的空格

str_trim.stringByTrimmingCharactersInSet(NSCharacterSet(charactersInString: "! "))//"hi  !23" 去掉两边的空格和‘!’ ，把 字符串中的每个字符进行了分解并去除