使用String字面量给常量赋值
let string = "string literal value"
常量string将会自动推断为String类型
初始化一个空的String
var emptyStr = "" //使用空字符串字面量 var anotherEmptyStr = String() //使用构造方法 //两者没有区别
使用isEmpty判断空String:
if emptyStr.isEmpty { print("have nothing here") }
String的可变性
使用“+”连接字符串,当然也支持自加运算符”+=”
var variableStr = "LastName" variableStr += "and FirstName" /// variableStr is "LastName and FirstName" //**but if: let constantStr = "Gender" constantStr += "and another Highlander" ///编译器会报错,被声明为常量的字符串不能被修改!
跟oc不同,swift的String通过var/let 变量/常量 标识决定其是否可变(can be mutated),而不需要选择NSString 还是 NSMutableString。
String是值类型
区别引用类型,在String在方法间传递,或者将其赋值给一个常量或者变量时,该String将会被复制(copy),而不是指向原来的对象。
String跟Characters的连接
let str = "hello world " let char: Character = "!" str.append(char) // 结果str为: "hello world !"
遍历String
for char in "myStr".characters { print(char) } //m //y //S //t //r
字符串插值
在字符串中插入常量变量表达式等,构造一个新的字符串”通过()”:
let multiplier = 3 let message = "\(multiplier) times 2.5 is \(Double(multiplier) * 2.5)" /// message is "3 times 2.5 is 7.5"
String中使用转义字符
在字符串中输入反斜线”\” 水平制表符”t” 换行”n” 双引号”“” 单引号”’” 等都需要在前面添加”\”进行转义,同时可以在转义字符后添加Unicode来进行特殊符号表情的显示:
//**双引号转义 let wiseWords = "\"Imagination is more important than knowledge\" - Einstein" ///"Imagination is more important than knowledge" - Einstein //**Unicode转义 let dollarSign = "\u{24}" let blackHeart = "\u{2665}" let sparklingHeart = "\u{1F496}" //**扩展自行集 //**对应关系 // \u{D55C}----한 // \u{1112}----ᄒ // \u{1161}----ᅡ // \u{11AB}----ᆫ let KoreaStr = "\u{D55C}\u{1112}\u{1161}\u{11AB}"
String长度
string.characters.count
let str = "1234567890" print("str has \(str.characters.count) characters") //输出 "star has 10 characters" //**为String增加笔画不会造成长度增加: var str = "cafe" print("the number of characters in \(word) is \(word.characters.count)") // 输出 "the number of characters in cafe is 4" //**now append some Unicode: word += "\u{301}" print("the number of characters in \(word) is \(word.characters.count)") //输出 "the number of characters in café is 4" //仅仅是改变了最后一个字符,并没有增加字符串的长度
正因为swift支持扩展字形集,不同的字符,和相同的不同表示的字符可能需要不同量的存储器来存储,所以在swift中characters所占用的存储量是不一定相同的,因此不能像oc计算NSString那样使用字符串来迭代计算,而应该遍历字符串的characters来确定字符串的长度。
访问和修改字符串
字符串索引
swift中的字符串具有相关连的索引类型(String.Index),可对应其每个位置的Character
正如上面所说,不同的字符串可能需要不同数量的内存来存储,所以为了确定哪些character在特定的位置上,我们必须遍历确定每个Unicode的开始结束位置,因此,String不能使用整形作索引。
startIndex:访问String第一个位置的字符 endIndex: 访问String最后一个位置的字符
(一个空的字符串或者长度为1的字符串,startIndex和endIndex相等)
predecessor(),successor(),advancedBy()一个String.Index值可以通过调用predecessor()方法来访问其前一个index,调用successor()来访问其后一个index,或者调用advancedBy()来指定访问相对位置的index( 之后5位的index: advancedBy(5) 往前5位的index: advancedBy(-5) )
let greeting = "Guten Tag!" greeting[greeting.startIndex] //G greeting[greeting.endIndex.predecessor()] //! greeting[greeting.startIndex.successor()] //u let index = greeting.startIndex.advancedBy(7) //a greeting[index] //输出 a
indiced : 字符串Index的集合
for index in greeting.characters.indices { print("\(greeting[index])",terminator: " ") } ///prints "G u t e n T a g !"
插入/移除
利用index,在制定位置插入字符character
var helloStr = "hello" helloStr.insert("~",atIndex: helloStr.endIndex) // hello~
同理,插入字符串(字符的集合)
var helloStr = "hello!" helloStr.insertContentOf(" world!".characters,at: hello.endIndex) // hello! world //用上面的知识,再追求下完美: var helloStr = "hello!" helloStr.insertContentOf(" world".characters,at: hello.endIndex.predecessor()) // hello world!
移除(index):
var helloStr = "hello world!" helloStr.removeAtIndex(helloStr.endIndex.predecessor()) // hello world //注意: // endIndex是指最后一个index位(将要输入内容的index位) //所以删除最后一个字符使用的index是endIndex.predecessor()(将要输入内容的index的前一个index位) //而不是endIndex
移除(Range):
var helloStr = "hello world!" let range = Range(start: helloStr.endIndex.advancedBy(-6),end: helloStr.endIndex.predecessor()) // 顺便贴一个new Range的简易写法: // let range = helloStr.endIndex.advancedBy(-6)..<helloStr.endIndex // 效果是一样的 helloStr.removeRange(range) // hello
字符串比较
两个纯字符串比较
let oneStr = "We're a lot alike,you and I." let anotherStr = "We're a lot alike,you and I." if oneStr == anotherStr { print("These two strings are considered equal") } //输出: These two strings are considered equal //相等
两个由characters组成的字符串比较
let oneStr = "Voulez-vous un caf\u{E9}?" //Voulez-vous un café? let anotherStr = "Voulez-vous un caf\u{65}\u{301}?" //Voulez-vous un café? //两者虽然看起来内容字符不同,其实\u{65}\u{301}是一个e和一个音调符号,根据上面的知识,结果组合成é(\u{E9}) if oneStr == anotherStr { print("These two strings are considered equal") } //输出: These two strings are considered equal //相等
两个表现相同的character比较
let oneChar: Character = "\u{41}" //拉丁字母中的A let anotherChar: Character = "\u{0410}" //西里尔字母中的A if oneChar != anotherChar { print(These two characters are not equivalent) } //输出: These two characters are not equivalent //不相等!
前缀和后缀的比较 我们可以使用hasPrefix()方法和hasSuffix()去匹配String的前缀和后缀,并返回一个Boolean值
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" ] //----遍历这个字符数组,匹配下前缀看看效果 var count = 0 for str in romeoAndJuliet { if str.hasPrefix("Act 1 ") { count++ } } print("There are \(count) string with Act 1 ") // 输出: "There are 5 string with Act 1" //----后缀呢 var count = 0 for str in romeoAndJuliet { if str.hasSuffix("Capulet's mansion") { count++ } } print("There are \(count) mansion string") // 输出: "There are 6 mansion stressing"
String使用UTF-8编码表示
复习一下,上面也提到,Swift中的String支持emoji表情和众多特殊字符,这也是String一个单位长度不一定等于两个character(汉字)或者1个character(英文字母)的原因。 先回到我们的话题。String和UTF-8的对应关系,我们来看一张官方电子书中的表: ![]/content/images/2015/12/utf8.png()
//上图中对应的String: //let dogString = "Dog!!" //同时String中的UTF-8编码也是可以像char那样遍历的 for unitCode in dogString.utf8 { print("\(unitCode) ",terminator: "") } //输出: 68 111 103 226 128 188 240 159 144 182
同理String也可以以UTF-16 和Unicode的方式遍历
for unitCode in dogString.utf16 { } for scalar in dogString.unicodeScalars { print("\(scalar.value) ",terminator: "") } // 68 111 103 8252 128054 for scalar in dogString.unicodeScalars { print("\(scalar) ",terminator: "") } // D o g !! //注意: 直接printunicodeScalar的话跟String的输出是一样效果的 //我们print出他的value,才是我们想要的编码