Swift 中的字符串操作

Update: Swift 4

• 字符串截取

var string = "www.stackoverflow.com"

var index = string.index(string.startIndex, offsetBy: 17)
var substring0 = string[string.startIndex..<index] // www.stackoverflow
var substring1 = string[index..<string.endIndex]   // .com
// 或(Swift4 新增语法糖)
var substring2 = string[..<index] // www.stackoverflow
var substring3 = string[index...] // .com

var substring4 = string[string.index(string.startIndex, offsetBy: 4)..<index] // stackoverflow

// 掐头去尾
let substring5 = String(string.characters.dropFirst(4)) // stackoverflow.com
let substring6 = String(string.characters.dropLast(4)) // www.stackoverflow

• 删除空格

var string = " www.stackoverflow.com "

// 删除两端空格
string.trimmingCharacters(in: CharacterSet.whitespaces)
// 删除两端空格和换行符
string.trimmingCharacters(in: CharacterSet.whitespacesAndNewlines)

• 范围替换

var string = "www.stackoverflow.com"

let range = string.index(string.startIndex, offsetBy: 4)..<string.index(string.endIndex, offsetBy: -4)
string.replaceSubrange(range, with: "segmentfault") // www.segmentfault.com

• String 转 Int

let string = "123"          // "123"
let intValue = Int(string)  // 123

• String 转 Double

let string = "3.1415926"          // "3.1415926"
let doubleValue = Double(string)  // 3.1415926