Swift 字符串String

OC的字符串是NSString，swift中字符串类型时String
String 是一个结构体，性能更高
NSString是一个OC对象，性能略差
String支持直接遍历
Swift提供了String和NSString之间的无缝转换

let cname="jack"

let age=18

let height=1.87

let infoStr="my name is \(cname),age is\(age),heiht is \(height)"

 

 

//字符串格式化 03:04

let min=3

let second=4

let timeStr=String(format: "%02d:%02d", min,second)

 

let str=String("adfsfds")

 

//字符串的截取

let urlString="www.abcde.com"

//方式一

//将String类型转成NSString类型，再进行截取 as NSString

let header1=(urlString as NSString).substring(to: 3)

let middle1=(urlString as NSString).substring(with: NSMakeRange(4, 5))

let footer1=(urlString as NSString).substring(from: 10)

 

//方式二

let headerIndex=urlString.index(urlString.startIndex, offsetBy: 3)

//String[range]的返回类型为String.SubSequence，表示返回的是原string的子集，两者的内存是一样的。

//想要获取一份新的string需要使用以下方法

let SubSequence=urlString[..<headerIndex]

let header2=String(SubSequence)

 

let middleIndex1=urlString.index(urlString.startIndex, offsetBy: 4)

let middleIndex2=urlString.index(urlString.startIndex, offsetBy: 8)

let range2:ClosedRange=middleIndex1...middleIndex2

let middle2=String(urlString[range2])

 

let footerIndex1=urlString.index(urlString.endIndex, offsetBy: -3)

let range3:PartialRangeFrom=footerIndex1...

let footer2=urlString[range3]