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📜  Swift-字符串

📅  最后修改于: 2020-12-25 04:27:51             🧑  作者: Mango

Swift 4中的字符串是字符的有序集合，例如“ Hello，World！”。它们由Swift 4数据类型String表示，该数据类型又表示字符类型的值的集合。

创建一个字符串

您可以通过使用字符串字面量或创建String类的实例来创建字符串，如下所示：

现场演示
// String creation using String literal
var stringA = "Hello, Swift 4!"
print( stringA )

// String creation using String instance
var stringB = String("Hello, Swift 4!")
print( stringB )

//Multiple line string

let stringC = """
Hey this is a
example of multiple Line
string by tutorialsPoint 

"""
print(stringC)

编译并执行上述代码后，将产生以下结果

Hello, Swift 4!
Hello, Swift 4!
Hey this is a
example of multiple Line
string by tutorialsPoint

空字符串

您可以通过使用空字符串字面量或创建String类的实例来创建空字符串，如下所示。您还可以使用布尔属性isEmpty检查字符串是否为空。

现场演示
// Empty string creation using String literal
var stringA = ""

if stringA.isEmpty {
   print( "stringA is empty" )
} else {
   print( "stringA is not empty" )
}

// Empty string creation using String instance
let stringB = String()

if stringB.isEmpty {
   print( "stringB is empty" )
} else {
   print( "stringB is not empty" )
}

编译并执行上述代码后，将产生以下结果-

stringA is empty
stringB is empty

字符串常量

您可以通过将String分配给变量来指定是对其进行修改(或变异)，还是使用let关键字将其分配给常量来将其保持不变，如下所示-

// stringA can be modified
var stringA = "Hello, Swift 4!"
stringA + = "--Readers--"
print( stringA )

// stringB can not be modified
let stringB = String("Hello, Swift 4!")
stringB + = "--Readers--"
print( stringB )

编译并执行上述代码后，将产生以下结果-

Playground execution failed: error: :10:1: error: 'String' is not
convertible to '@lvalue UInt8'
stringB + = "--Readers--"

字符串插值

字符串插值是通过将常量，变量，字面量和表达式的值包含在字符串字面量来构造新的String值的方法。

您插入字符串字面量的每个项目(变量或常量)都用一对括号括起来，并以反斜杠为前缀。这是一个简单的例子-

现场演示
var varA = 20
let constA = 100
var varC:Float = 20.0

var stringA = "\(varA) times \(constA) is equal to \(varC * 100)"
print( stringA )

编译并执行上述代码后，将产生以下结果-

20 times 100 is equal to 2000.0

字符串串联

您可以使用+运算符来连接两个字符串或一个字符串和一个字符或两个字符。这是一个简单的例子-

现场演示
let constA = "Hello,"
let constB = "World!"

var stringA = constA + constB
print( stringA )

编译并执行上述代码后，将产生以下结果-

Hello,World!

弦长

Swift 4字符串没有length属性，但是您可以使用global count()函数对字符串的字符数进行计数。这是一个简单的例子-

现场演示
var varA = "Hello, Swift 4!"

print( "\(varA), length is \((varA.count))" )

编译并执行上述代码后，将产生以下结果-

Hello, Swift 4!, length is 15

字符串比较

您可以使用==运算符比较两个字符串变量或常量。这是一个简单的例子-

现场演示
var varA = "Hello, Swift 4!"
var varB = "Hello, World!"

if varA == varB {
   print( "\(varA) and \(varB) are equal" )
} else {
   print( "\(varA) and \(varB) are not equal" )
}

编译并执行上述代码后，将产生以下结果-

Hello, Swift 4! and Hello, World! are not equal

字符串迭代

字符串再次是swift 4中值的集合，因此我们可以使用循环在字符串进行迭代。 –

现场演示
for chars in "ThisString" {
   print(chars, terminator: " ")
}

编译并执行上述代码后，将产生以下结果-

T h i s S t r i n g

Unicode字符串

您可以通过迭代字符串的utf8和utf16属性来访问字符串的UTF-8和UTF-16表示形式，如以下示例所示-

现场演示
var unicodeString = "Dog???"

print("UTF-8 Codes: ")
for code in unicodeString.utf8 {
   print("\(code) ")
}

print("\n")

print("UTF-16 Codes: ")
for code in unicodeString.utf16 {
   print("\(code) ")
}

编译并执行上述代码后，将产生以下结果-

UTF-8 Codes: 
68 
111 
103 
63 
63 
63 


UTF-16 Codes: 
68 
111 
103 
63 
63 
63

字符串函数和运算符

Swift 4支持与字符串有关的各种方法和运算符-

Sr.No Functions/Operators & Purpose
1

isEmpty

A Boolean value that determines whether a string is empty or not.
2

hasPrefix(prefix: String)

Function to check whether a given parameter string exists as a prefix of the string or not.
3

hasSuffix(suffix: String)

Function to check whether a given parameter string exists as a suffix of the string or not.
4

toInt()

Function to convert numeric String value into Integer.
5

count()

Global function to count the number of Characters in a string.
6

utf8

Property to return a UTF-8 representation of a string.
7

utf16

Property to return a UTF-16 representation of a string.
8

unicodeScalars

Property to return a Unicode Scalar representation of a string.
9

+

Operator to concatenate two strings, or a string and a character, or two characters.
10

+=

Operator to append a string or character to an existing string.
11

==

Operator to determine the equality of two strings.
12

<

Operator to perform a lexicographical comparison to determine whether one string evaluates as less than another.
13

startIndex

To get the value at starting index of string.
14

endIndex

To get the value at ending index of string.
15

Indices

To access the indeces one by one. i.e all the characters of string one by one.
16

insert(“Value”, at: position)

To insert a value at a position.
17

remove(at: position)

removeSubrange(range)

to remove a value at a position, or to remove a range of values from string.
18

reversed()

returns the reverse of a string