Swift结构体指针操作
shannon
8年前
<h2><strong>C语言的指针操作</strong></h2> <p><strong>在c语言中申明一个变量并通过指针修改该变量的值</strong></p> <pre> <code class="language-swift">int a = 1; int *p = &a; *p = 2; printf("a value is %d\\\\n",a);</code></pre> <p><strong>a value is 2</strong></p> <p><strong>c语言操作结构体指针操作</strong></p> <ul> <li> <p>申明一个叫User的结构体</p> </li> </ul> <pre> <code class="language-swift">typedef struct User{ int ID; int age; } User;</code></pre> <ul> <li> <p>申明一个结构体User变量user 设置ID值为1 age值为18</p> </li> </ul> <pre> <code class="language-swift">User user; user.ID = 1; user.age = 3;</code></pre> <ul> <li> <p>通过指针对变量user的值进行修改</p> </li> </ul> <pre> <code class="language-swift">//申明一个结构体指针变量userpointer指向user的地址 User *userpointer = &user; //修改ID的值为2 int *idPointer = (int *)userpointer; *idPointer = 2; //获得属性age所在指针 int *agePointer = ++ idPointer; //修改user的age值为4 *agePointer = 4; printf("user ID = %d, age = %d", user.ID, user.age);</code></pre> <p><strong>user ID = 2, age = 4</strong></p> <h2><strong>Swift</strong></h2> <p>Swift并不推荐对指针进行直接操作, 但仍提供了几种可以直接操作内存的指针类型，以下是c与Swift的语法对应表 ，使用 Type 做类型占用</p> <p>对于返回值、变量和参数，使用一下对应表</p> <table> <thead> <tr> <th>C 语法</th> <th>Swift 语法</th> </tr> </thead> <tbody> <tr> <td>const Type *</td> <td>UnsafePointer</td> </tr> <tr> <td>Type *</td> <td>UnsafeMutablePointer</td> </tr> </tbody> </table> <p>对于类，使用一下语法对应</p> <table> <thead> <tr> <th>C 语法</th> <th>Swift 语法</th> </tr> </thead> <tbody> <tr> <td>Type <em>const</em></td> <td>UnsafePointer</td> </tr> <tr> <td>Type <em>__strong</em></td> <td>UnsafeMutablePointer</td> </tr> <tr> <td>Type **</td> <td>AutoreleasingUnsafeMutablePointer</td> </tr> </tbody> </table> <p>在Swift中无类型的指针，原始内存可以用UnsafeRawPointer 和UnsafeMutableRawPointer来表示</p> <p>如果像不完整结构体的这样的c指针的值的类型无法用Swift来表示，则用OpaquePointer来表示</p> <p><strong>接下来，进行Swift版结构体指针操</strong>作</p> <p>申明User结构体</p> <pre> <code class="language-swift">struct User { var ID: Int var age: Int }</code></pre> <p>申明变量，并获取变量地址, 创建一个user变量 ID初始值问为1 age初始值为3</p> <p>通过指针设置ID值为2 设置age值为3</p> <pre> <code class="language-swift">var user = User(ID: 1, age: 3) let userPointer = withUnsafePointer(to: &user, {$0})//UnsafePointer //打印user指针的值 print(userPointer.pointee) //User(ID: 1, age: 3) //获取user ID的指针 let userIDPointer = unsafeBitCast(userPointer, to: UnsafeMutablePointer .self) //设置ID的值为2 userIDPointer.pointee = 2 print(userPointer.pointee) //User(ID: 2, age: 3) //获取user age的指针 let agePointer = userIDPointer.advanced(by: 1) agePointer.pointee = 4 print(userPointer.pointee) //User(ID: 2, age: 4) </code></pre> <p><strong>虽然c和Swift的语法差距有点大，但是原理是相同的</strong></p> <p>接下来我们看一个更复杂一点的例子</p> <pre> <code class="language-swift">public struct Person { var age: Int var firstName: String var lastName: String var phoneNumber: PhoneNumber } public struct PhoneNumber { var number: String var type: String }</code></pre> <p>创建person变量 并通过指针操作 获取对应的属性值</p> <pre> <code class="language-swift">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> <p>到这里，我们已经学会了 通过指针获取值，通过指针设置对应的值</p> <p>接下来 就可以运用这些知识发挥自己的创造力了</p> <p><strong>参考资料</strong></p> <p><a href="/misc/goto?guid=4959721632613144169" rel="nofollow,noindex">结构体的内存空间分配原理</a></p> <p><a href="/misc/goto?guid=4959721632704307919" rel="nofollow,noindex">Swift 中的指针使用</a></p> <p>文章转自 <a href="/misc/goto?guid=4959721632787158299" rel="nofollow,noindex">冰琳92的简书</a></p> <p> </p> <p>来自：http://www.cocoachina.com/swift/20161020/17802.html</p> <p> </p>