let softWrappedQuotation =""" The White Rabbit put on his spectacles. "Where shall I begin, \ please your Majesty?" he asked. "Begin at the beginning," the King said gravely, "and go on \ till you come to the end; then stop." """
let lineBreaks =""" This string starts with a line break. It also ends with a line break. """
缩进的时候。下面这样写不会有多余的空格。
let lineBreaks =""" This string starts with a line break. It also ends with a line break. """
字符串中有下面这些特殊字符。
转意特殊字符，\0 空字符串，\\ 反斜杠，\t tab，\n line feed，\r 回车，\" 双引号，\' 单引号。
Unicode 字符 \u{n}。n 是 1-8 位的十六进制数字。
let wiseWords ="\"Imagination is more important than knowledge\" - Einstein" // "Imagination is more important than knowledge" - Einstein let dollarSign ="\u{24}"// $, Unicode scalar U+0024 let blackHeart ="\u{2665}"// ♥, Unicode scalar U+2665 let sparklingHeart ="\u{1F496}"// 💖, Unicode scalar U+1F496
声明一个空字符串。
var emptyString =""// empty string literal var anotherEmptyString =String() // initializer syntax // these two strings are both empty, and are equivalent to each other
判断一个字符串是否为空。
if emptyString.isEmpty { print("Nothing to see here") } // Prints "Nothing to see here"
修改字符串。
var variableString ="Horse" variableString +=" and carriage" // variableString is now "Horse and carriage"
let constantString ="Highlander" constantString +=" and another Highlander" // this reports a compile-time error - a constant string cannot be modified
for character in"Dog!🐶" { print(character) } // D // o // g // ! // 🐶
如果要声明一个字符变量需要提供类型。
let exclamationMark: Character="!"
字符数组可以初始化一个字符串。
let catCharacters: [Character] = ["C", "a", "t", "!", "🐱"] let catString =String(catCharacters) print(catString) // Prints "Cat!🐱"
链接字符串
可以用字符串的 append 方法将一个字符加入到字符串。
let string1 ="hello" let string2 =" there" var welcome = string1 + string2 // welcome now equals "hello there" let exclamationMark: Character="!" welcome.append(exclamationMark) // welcome now equals "hello there!"
let badStart =""" one two """ let end =""" three """ print(badStart + end) // Prints two lines: // one // twothree
let goodStart =""" one two """ print(goodStart + end) // Prints three lines: // one // two // three
字符串插值
模版字符串。
let multiplier =3 let message ="\(multiplier) times 2.5 is \(Double(multiplier) *2.5)" // message is "3 times 2.5 is 7.5"
字符计数
字符串的 .count 可以获得字符的计数。
let unusualMenagerie ="Koala 🐨, Snail 🐌, Penguin 🐧, Dromedary 🐪" print("unusualMenagerie has \(unusualMenagerie.count) characters") // Prints "unusualMenagerie has 40 characters"
swift 对 character 类型值使用扩展的字位簇（grapheme clusters），这意味着字符串的拼接和修改并不总是会影响字符串的长度。例如给 cafe 这个单词加上法语的重音符号，修改后的字符串仍然是 4 位。
var word ="cafe" print("the number of characters in \(word) is \(word.count)") // Prints "the number of characters in cafe is 4"
word +="\u{301}"// COMBINING ACUTE ACCENT, U+0301
print("the number of characters in \(word) is \(word.count)") // Prints "the number of characters in café is 4"
let greeting ="Guten Tag!" greeting[greeting.startIndex] // G greeting[greeting.index(before: greeting.endIndex)] // ! greeting[greeting.index(after: greeting.startIndex)] // u let index = greeting.index(greeting.startIndex, offsetBy: 7) greeting[index] // a
welcome.remove(at: welcome.index(before: welcome.endIndex)) // welcome now equals "hello there"
let range = welcome.index(welcome.endIndex, offsetBy: -6)..<welcome.endIndex welcome.removeSubrange(range) // welcome now equals "hello"
分隔字符串。
let greeting ="Hello, world!" let index = greeting.firstIndex(of: ",") ?? greeting.endIndex let beginning = greeting[..<index] // beginning is "Hello"
// Convert the result to a String for long-term storage. let newString =String(beginning)
前缀和后缀。
let romeoAndJuliet = [ "Act 1 Scene 1: Verona, A public place", "Act 1 Scene 2: Capulet's mansion", "Act 1 Scene 3: A room in Capulet's mansion", "Act 1 Scene 4: A street outside Capulet's mansion", "Act 1 Scene 5: The Great Hall in Capulet's mansion", "Act 2 Scene 1: Outside Capulet's mansion", "Act 2 Scene 2: Capulet's orchard", "Act 2 Scene 3: Outside Friar Lawrence's cell", "Act 2 Scene 4: A street in Verona", "Act 2 Scene 5: Capulet's mansion", "Act 2 Scene 6: Friar Lawrence's cell" ]
var act1SceneCount =0 for scene in romeoAndJuliet { if scene.hasPrefix("Act 1 ") { act1SceneCount +=1 } } print("There are \(act1SceneCount) scenes in Act 1") // Prints "There are 5 scenes in Act 1"
var mansionCount =0 var cellCount =0 for scene in romeoAndJuliet { if scene.hasSuffix("Capulet's mansion") { mansionCount +=1 } elseif scene.hasSuffix("Friar Lawrence's cell") { cellCount +=1 } } print("\(mansionCount) mansion scenes; \(cellCount) cell scenes") // Prints "6 mansion scenes; 2 cell scenes"