Question

更新到Swift 3后，我的代码有点问题。转换前我有这个代码：

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

我将它转换为此代码，在第3行我得到了错误

...无法转换类型的值＆＃39; UnsafeMutablePointer＆＃39;预期参数类型＆＃39; UnsafeMutablePointer＆＃39;

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()
  }
}

有谁知道怎么摆脱这个？

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”的数量作为参数，而不是数量字节）。

但请注意，您的方法会泄漏内存，分配内存被取消初始化（move()）但也必须解除分配的：

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
    }
}

更简单的解决方案是（来自 {{3}}）：

extension Data {
    func castToCPointer<T>() -> T {
        return self.withUnsafeBytes { $0.pointee }
    }
}

Answer 2

您还可以在扩展程序

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：无法转换类型＆＃39; UnsafeMutablePointer＆＃39;预期参数类型＆＃39; UnsafeMutablePointer＆＃39;

2 个答案: