Swift: 无法将类型 'UnsafeMutablePointer' 的值转换为预期的参数类型 'UnsafeMutablePointer'

Question

更新到 Swift 后我的代码有点问题 3. 我在转换前有这个代码：

extension NSData {
  func castToCPointer<T>() -> T {
    let mem = UnsafeMutablePointer<T>.alloc(sizeof(T.Type))
    self.getBytes(mem, length: sizeof(T.Type))
    return mem.move()
  }
}

然后我将其转换为此代码，在第 3 行出现错误

... Cannot convert value of type 'UnsafeMutablePointer' to expected argument type 'UnsafeMutablePointer'

extension Data {
  func castToCPointer<T>() -> T{
    let mem = UnsafeMutablePointer<T>.allocate(capacity: MemoryLayout<T.Type>.size)
    self.copyBytes(to: mem, count: MemoryLayout<T.Type>.size)
    //self.copyBytes(to: mem, count: MemoryLayout<T.Type>.size)
    return mem.move()
  }
}

有谁知道如何摆脱这个？

Answer 1

copyBytes 期望 UnsafeMutableBufferPointer 作为参数：

extension Data {
    func castToCPointer<T>() -> T {
        let mem = UnsafeMutablePointer<T>.allocate(capacity: 1)
        _ = self.copyBytes(to: UnsafeMutableBufferPointer(start: mem, count: 1))
        return mem.move()
    }
}

(allocate() 将 "items" 的个数作为参数，而不是字节。)

但是注意你的方法会泄漏内存，分配的内存被取消初始化（move()）但也必须是释放：

extension Data {
    func castToCPointer<T>() -> T {
        let mem = UnsafeMutablePointer<T>.allocate(capacity: 1)
        _ = self.copyBytes(to: UnsafeMutableBufferPointer(start: mem, count: 1))
        let val =  mem.move()
        mem.deallocate(capacity: 1)
        return val
    }
}

一个更简单的解决方案是（来自 ):

extension Data {
    func castToCPointer<T>() -> T {
        return self.withUnsafeBytes { [=12=].pointee }
    }
}

Answer 2

您还可以在扩展中使用以下语法

extension Data {
    func castToCPointer<T>() -> T {
        var bytes = self.bytes
        var val = withUnsafePointer(to: &bytes) { (temp) in
            return unsafeBitCast(temp, to: T.self)
        }
        return val
    }
}

var data:NSData/NSMutableData
var bytes = data.bytes
var val = withUnsafePointer(to: &bytes) { (temp) in
   return unsafeBitCast(temp, to: T.self)
}

Swift: 无法将类型 'UnsafeMutablePointer' 的值转换为预期的参数类型 'UnsafeMutablePointer'

Swift: Cannot convert value of type 'UnsafeMutablePointer' to expected argument type 'UnsafeMutablePointer'

swift

unsafemutablepointer