swift-字符串的截取

// 1, 字符串的截取let url = "www:xiaoyu.com"// 1.1 方式一：将string类型转成nsstring   as NSStringlet header = (url as NSString).substring(to: 3)let range = NSMakeRange(4, 8)let middle = (url as NSString).substring(with: range)// 1.2 方式二：直接使用stringlet headerIndex = url.index(url.startIndex, offsetBy: 3)let header1 = url.substring(to: headerIndex)let startIndex = url.index(url.startIndex, offsetBy: 4)let endIndex = url.index(url.startIndex, offsetBy: 10)let range2 = Range(startIndex..<endIndex)let middle2 = url.substring(with: range2)let strart3 = url.index(url.startIndex, offsetBy: 11)let end3 = url.index(url.startIndex, offsetBy: 14)let rang3 = Range(strart3..<end3)let endStr = url.substring(with: rang3)