swift5处理子字符串 swift 字符串长度

let someString = "Some string literal Value"

字符串字面两包括以下特殊字符：
1.转义特殊字符 \0 (空字符)、\(反斜线)、\t (水平制表符)、\n (换行符)、\r (回车符)、\” (双引号)、\’ (单引号)。
2.单字节 Unicode 标量,写成 \xnn,其中 nn 为两位十六进制数。
3.双字节 Unicode 标量,写成 \unnnn,其中 nnnn 为四位十六进制数。
4.四字节 Unicode 标量,写成 \Unnnnnnnn,其中 nnnnnnnn 为八位十六进制数

let wiseWords = "\"Imageination is more important than knowledge\"-Einstein"
／／""Imageination 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

初始化空字符串

var emptyString = ""
var anotherEmptyString = String()

通过检查 Boolean 类型的 isEmpty 属性来判断该字符串是否为空

if emptyString.isEmpty {
    print("Nothing to see here")
}
// Prints "Nothing to see here"

使用字符(Characters)

for character in "Dog!��".characters {
    print(character)
}
// D
// o
// g
// !
// ��

• 字符串可变性
• 通过将一个特定字符串分配给一个变量(对其进行修改)或者常量(保证其不会被修改)来指定该字符串是否可以被修

var variableString = "Horse"
variableString += "add carriage"

for-in 循环在 For Loops 中

let exclamationMark: Character = "!"

let catCharacters: [Character] = ["C", "a", "t", "!", "��"]
let catString = String(catCharacters)
print(catString)
// Prints "Cat!��"

//连接字符串和字符: 通过加法运算符 (+) 
let string1 = "hello"
let string2 = " there"
var welcome = string1 + string2
// prints: "hello there"

//也可以通过加法赋值运算符 (+=) 
var instruction = "look over"
instruction += string2
// instruction now equals "look over there"

//使用 append（）方法
 welcome.append(exclamationMark)
// welcome now equals "hello there!"

使用字符(Characters),利用for－in循环来遍历字符串的每一个字符

for char in "dog".characters {
    print(char)
}

字符串插值

let multiplier = 3
let message = "\(multiplier) times 2.5 is \(Double(multiplier) * 2.5)"

字符串长度

let unusualMenagerie = "Koala ��, Snail ��, Penguin ��, Dromedary ��"
print("unusualMenagerie has \(unusualMenagerie.characters.count) characters")
// Prints "unusualMenagerie has 40 characters"


var word = "cafe"
print("the number of characters in \(word) is \(word.characters.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.characters.count)")
// Prints "the number of characters in café is 4"

*访问和修改字符串
*可以通过其方法和属性，或者下标，来访问或者修改字符串
*字符串索引swift的字符串具有相关联的索引类型(String.Index),可对应其没个位置的Character
*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.advancedBy(2)] //t

indiced:字符串Index的集合

for index in greeting.characters.indices {
    print("\(greeting[index])",terminator:"!")
}
// G!u!t!e!n! !T!a!g!!!

插入/移除

//插入／移除 insert(_:atIndex:)方法
var welcome1 = "hello"
welcome.insert("!", atIndex: welcome1.endIndex)
// welcome now equals "hello!"

//使用insertContentsOf(_:at:) 方法
welcome.insertContentsOf(" there".characters, at: welcome.endIndex.predecessor())
// welcome now equals "hello there!"

//使用removeAtIndex(_:)方法
welcome.removeAtIndex(welcome.endIndex.predecessor())
// welcome now equals "hello there"

//使用removeRange(_:)方法
let range = welcome.endIndex.advancedBy(-6)..<welcome.endIndex
welcome.removeRange(range)
// welcome now equals "hello"

移除（index）

var helloStr3 = "hello world!"
let range = helloStr3.endIndex.advancedBy(-6) ..< helloStr3.endIndex //6..<12
helloStr3.removeRange(range)  //"hello"

字符串比较
字符串相等

let quotation = "We're a lot alike, you and I."
let sameQuotation = "We're a lot alike, you and I."
if quotation == sameQuotation {
    print("These two strings are considered equal")
}
// Prints "These two strings are considered equal"

前缀和后缀比较 使用 hasPrefix()和hasSuffix()去匹配String的前缀和后缀返回一个Boolean

let remeoAndJuliet = [
    "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"
]
//遍历字符数组 匹配前缀
var count = 0
for str in remeoAndJuliet {
    if str.hasPrefix("Act 1") {
        count++
    }
}
print("There are \(count) string with Act 1")
//"There are 5 string with Act 1\n"

利用 hasPrefix 方法使用 romeoAndJuliet 数组来计算话剧中第一幕的场景数:

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"

使用 hasSuffix 方法来计算发生在 Capulet 公馆和 Lawrence 牢房内以及周围的场 景数。

var mansionCount = 0
var cellCount = 0
for scene in romeoAndJuliet {
    if scene.hasSuffix("Capulet's mansion") {
        mansionCount += 1
    } else if scene.hasSuffix("Friar Lawrence's cell") {
        cellCount += 1
    }
}
print("\(mansionCount) mansion scenes; \(cellCount) cell scenes")
// Prints "6 mansion scenes; 2 cell scenes"

大写和小写字符串

let normal = "Could you help me, please"
let shouty = normal.uppercaseString  //"COULD YOU HELP ME, PLEASE"
let whispered = normal.lowercaseString //"could you help me, please"
let captital = normal.capitalizedString //"Could You Help Me, Please"

Unicode 术语(Terminology)

let dogString = "Dog!????"

for codeUnit in dogString.utf8 {
    print("\(codeUnit)")
}
print("\n")
//68 111 103 33 240 159 144 182

for scalar in dogString.unicodeScalars {
    print("\(scalar) ")
    }
/*
D
o
g
!
?
?
?
?
*/