Swift string

Swift is a set of strings of characters. For example, the set of values of character type "Hello, World!" So ordered, its data typeString.

Creating strings

You can create an instance of the string by using a string literal or String class:

import Cocoa

// 使用字符串字面量
var stringA = "Hello, World!"
print( stringA )

// String 实例化
var stringB = String("Hello, World!")
print( stringB )

The above program execution output is:

Hello, World!
Hello, World!

Empty string

You can use an empty literal string assigned to the variable or initialize an instance of the String class to the initial value of an empty string. We can use isEmpty string property to determine whether a string is empty:

import Cocoa

// 使用字符串字面量创建空字符串
var stringA = ""

if stringA.isEmpty {
   print( "stringA 是空的" )
} else {
   print( "stringA 不是空的" )
}

// 实例化 String 类来创建空字符串
let stringB = String()

if stringB.isEmpty {
   print( "stringB 是空的" )
} else {
   print( "stringB 不是空的" )
}

The above program execution output is:

stringA 是空的
stringB 是空的

String Constants

You can assign a string to a variable or constant variable is modifiable, constants can not be modified.

import Cocoa

// stringA 可被修改
var stringA = "本教程："
stringA += "https://w3big.com"
print( stringA )

// stringB 不能修改
let stringB = String("本教程：")
stringB += "https://w3big.com"
print( stringB )

The output of the above program execution error will result, that stringB constant can not be modified:

error: left side of mutating operator isn't mutable: 'stringB' is a 'let' constant
stringB += "https://w3big.com"

Insert the string value

String interpolation is a new way to build a string that can contain constants, variables, literals, and expressions therein. Each insert your string literals are prefixed with a backslash in parentheses:

import Cocoa

var varA   = 20
let constA = 100
var varC:Float = 20.0

var stringA = "\(varA) 乘于 \(constA) 等于 \(varC * 100)"
print( stringA )

The above program execution output is:

20 乘于 100 等于 2000.0

String concatenation

Strings can be connected bya + sign, examples are as follows:

import Cocoa

let constA = "本教程："
let constB = "https://w3big.com"

var stringA = constA + constB

print( stringA )

The above program execution output is:

本教程：https://w3big.com

String length

String length is calculated usingString.characters.count properties, examples are as follows:

import Cocoa

var varA   = "w3big.com"

print( "\(varA), 长度为 \(varA.characters.count)" )

The above program execution output is:

w3big.com, 长度为 14

String comparison

You can use== to compare two strings are equal:

import Cocoa

var varA   = "Hello, Swift!"
var varB   = "Hello, World!"

if varA == varB {
   print( "\(varA) 与 \(varB) 是相等的" )
} else {
   print( "\(varA) 与 \(varB) 是不相等的" )
}

The above program execution output is:

Hello, Swift! 与 Hello, World! 是不相等的

Unicode strings

Unicode is an international standard for encoding text, Swift's String type is based on the Unicode built. You can loop iteration the string encoding UTF-8 and UTF-16, the examples are as follows:

import Cocoa

var unicodeString   = "本教程"

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

print("\n")

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

The above program execution output is:

UTF-8 编码: 
232 
143 
156 
233 
184 
159 
230 
149 
153 
231 
168 
139 
UTF-16 编码: 
33756 
40479 
25945 
31243 

String Functions and Operators

Swift supports the following string functions and operators:

let myString: String = "256"
let myInt: Int? = Int(myString)