Swift結構體指針操作
C語言的指針操作
在c語言中申明一個變量并通過指針修改該變量的值
int a = 1;
int p = &a;p = 2;
printf("a value is %d\\n",a);</code></pre>
a value is 2
c語言操作結構體指針操作
-
申明一個叫User的結構體
typedef struct User{
int ID;
int age;
} User;
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申明一個結構體User變量user 設置ID值為1 age值為18
User user;
user.ID = 1;
user.age = 3;
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通過指針對變量user的值進行修改
//申明一個結構體指針變量userpointer指向user的地址
User *userpointer = &user;
//修改ID的值為2
int idPointer = (int )userpointer;
*idPointer = 2;
//獲得屬性age所在指針
int agePointer = ++ idPointer;
//修改user的age值為4agePointer = 4;
printf("user ID = %d, age = %d", user.ID, user.age);</code></pre>
user ID = 2, age = 4
Swift
Swift并不推薦對指針進行直接操作, 但仍提供了幾種可以直接操作內存的指針類型，以下是c與Swift的語法對應表 ，使用 Type 做類型占用
對于返回值、變量和參數，使用一下對應表
C 語法
Swift 語法
const Type *
UnsafePointer
Type *
UnsafeMutablePointer
對于類，使用一下語法對應
C 語法
Swift 語法
Type const
UnsafePointer
Type __strong
UnsafeMutablePointer
Type **
AutoreleasingUnsafeMutablePointer
在Swift中無類型的指針，原始內存可以用UnsafeRawPointer 和UnsafeMutableRawPointer來表示
如果像不完整結構體的這樣的c指針的值的類型無法用Swift來表示，則用OpaquePointer來表示
接下來，進行Swift版結構體指針操作
申明User結構體
struct User {
var ID: Int
var age: Int
}
申明變量，并獲取變量地址, 創建一個user變量 ID初始值問為1 age初始值為3
通過指針設置ID值為2 設置age值為3
var user = User(ID: 1, age: 3)
let userPointer = withUnsafePointer(to: &user, {$0})//UnsafePointer
//打印user指針的值
print(userPointer.pointee)
//User(ID: 1, age: 3)
//獲取user ID的指針
let userIDPointer = unsafeBitCast(userPointer, to: UnsafeMutablePointer
.self) //設置ID的值為2 userIDPointer.pointee = 2 print(userPointer.pointee) //User(ID: 2, age: 3) //獲取user age的指針 let agePointer = userIDPointer.advanced(by: 1) agePointer.pointee = 4 print(userPointer.pointee) //User(ID: 2, age: 4)
</code></pre>
雖然c和Swift的語法差距有點大，但是原理是相同的
接下來我們看一個更復雜一點的例子
public struct Person {
var age: Int
var firstName: String
var lastName: String
var phoneNumber: PhoneNumber
}
public struct PhoneNumber {
var number: String
var type: String
}
創建person變量 并通過指針操作 獲取對應的屬性值
let phone = PhoneNumber(number: "186xxxxxxxx", type: "work")
var person = Person(age: 24, firstName: "Bing", lastName: "lin", phoneNumber: phone)
let rawPointer = withUnsafePointer(to: &person, { UnsafeRawPointer($0)})
let age = rawPointer.load(fromByteOffset: 0, as: Int.self)
let firstName = rawPointer.load(fromByteOffset: 8, as: String.self)
let lastName = rawPointer.load(fromByteOffset: 32, as: String.self)
let phoneInfo = rawPointer.load(fromByteOffset: 56, as: PhoneNumber.self)
print("age: \\(age) firstName: \\(firstName) lastName: \\(lastName) , phoneNumber: \\(phoneInfo)")
//age: 24 firstName: Bing lastName: lin , phoneNumber: PhoneNumber(number: "186xxxxxxxx", type: "work")</code></pre>
到這里，我們已經學會了 通過指針獲取值，通過指針設置對應的值
接下來 就可以運用這些知識發揮自己的創造力了
參考資料
文章轉自 冰琳92的簡書
來自：http://www.cocoachina.com/swift/20161020/17802.html