Swift 取子字符串

        let str =
"0123456�画画……％……"

        let s1 = (str
as NSString).substringFromIndex(3)

        print(s1)

        

        let index = str.startIndex.advancedBy(2)

        debugPrint(index.dynamicType)

        let s2 = str.substringFromIndex(index)

        print(s2)

        let tart = str.startIndex

        let end = str.endIndex.advancedBy(-1)

        let s3 = str.substringWithRange(tart..<end)

        print(s3)