Question

我试图转换此源代码：

BluetoothDeviceAddress *deviceAddress = malloc(sizeof(BluetoothDeviceAddress));

对斯威夫特来说，这给了我：

let deviceAddress: BluetoothDeviceAddress = malloc(sizeof(BluetoothDeviceAddress))

但是，我发现在Swift 3/4中，sizeof不再使用了，但这不是我的错误，Xcode返回：

＆＃34;无法转换类型＆＃39; UnsafeMutableRawPointer的值！＆＃39;指定类型＆＃39; BluetoothDeviceAddress＆＃39;＆＃34;

我尝试更改为malloc(MemoryLayout<BluetoothDeviceAddress>.size)，但仍然是同样的错误。

编辑：正如MartinR的评论中提出的那样，我尝试改为let deviceAddress = BluetoothDeviceAddress() 但是当我想初始化IOBluetoothDevice时，我仍然会收到错误（selectedDevice是IOBluetoothDevice的var）：

self.selectedDevice = IOBluetoothDevice(address: deviceAddress)

错误：无法转换类型＆＃39; BluetoothDeviceAddress＆＃39;的值预期参数类型＆＃39; UnsafePointer！＆＃39;

最佳，

安托

Answer 1

回答直接问题：从原始内容中获取键入的指针指针在Swift中称为“绑定”，并使用bindMemory()：

完成

let ptr = malloc(MemoryLayout<BluetoothDeviceAddress>.size)! // Assuming that the allocation does not fail
let deviceAddressPtr = ptr.bindMemory(to: BluetoothDeviceAddress.self, capacity: 1)
deviceAddressPtr.initialize(to: BluetoothDeviceAddress())
// Use deviceAddressPtr.pointee to access pointed-to memory ...

let selectedDevice = IOBluetoothDevice(address: deviceAddressPtr)
// ...

deviceAddressPtr.deinitialize(count: 1)
free(ptr)

不使用malloc / free，而是使用allocate / release方法斯威夫特的Unsafe(Mutable)Pointer：

let deviceAddressPtr = UnsafeMutablePointer<BluetoothDeviceAddress>.allocate(capacity: 1)
deviceAddressPtr.initialize(to: BluetoothDeviceAddress())
// Use deviceAddressPtr.pointee to access pointed-to memory ...

let selectedDevice = IOBluetoothDevice(address: deviceAddressPtr)
// ...

deviceAddressPtr.deinitialize(count: 1)
deviceAddressPtr.deallocate(capacity: 1)

参见SE-0107 UnsafeRawPointer API 有关原始指针和绑定的更多信息。

但是，通常更容易直接创建该类型的值并将其作为inout表达式传递给&。例如：

var deviceAddress = BluetoothDeviceAddress()
// ...

let selectedDevice = IOBluetoothDevice(address: &deviceAddress)
// ...

无法将UnsafeMutableRawPointer的值转换为BluetoothDeviceAddress

1 个答案: