swift中String和Character的使用与总结
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Stringvar 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!
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Stringfor 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
let wiseWords = ""Imagination is more important than knowledge" - Einstein"
///"Imagination is more important than knowledge" - Einstein
//**Unicode
let dollarSign = "u{24}" // $,Unicode scalar U+0024
let blackHeart = "u{2665}" // ?,Unicode scalar U+2665
let sparklingHeart = "u{1F496}" // ??,Unicode scalar U+1F496
//**扩展自行集
//**对应关系
// u{D55C}----?
// u{1112}----?
// u{1161}----?
// u{11AB}----?
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 cafe? 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
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 predecessor(),successor(),advancedBy() 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 cafu{E9}?"
//Voulez-vous un café?
let anotherStr = "Voulez-vous un cafu{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 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 strsing"
String使用UTF-8编码表示呢复习一下,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。 //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
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