如何在Swift 3中将UInt16转换为UInt8?

问题描述：

我想将UInt16转换为UInt8数组，但收到以下错误消息:

I want to convert UInt16 to UInt8 array, but am getting the following error message:

'init'不可用:使用'withMemoryRebound(to:capacity:_)' 暂时将内存视为另一种与布局兼容的类型.

'init' is unavailable: use 'withMemoryRebound(to:capacity:_)' to temporarily view memory as another layout-compatible type.

代码:

    let statusByte: UInt8 = UInt8(status)
    let lenghtByte: UInt16 = UInt16(passwordBytes.count)

    var bigEndian = lenghtByte.bigEndian

    let bytePtr = withUnsafePointer(to: &bigEndian) {
        UnsafeBufferPointer<UInt8>(start: UnsafePointer($0), count: MemoryLayout.size(ofValue: bigEndian))
    }

答

如错误消息所示，您必须使用withMemoryRebound() 将UInt16的指针重新解释为UInt8的指针:

As the error message indicates, you have to use withMemoryRebound() to reinterpret the pointer to UInt16 as a pointer to UInt8:

let bytes = withUnsafePointer(to: &bigEndian) {
    $0.withMemoryRebound(to: UInt8.self, capacity: MemoryLayout.size(ofValue: bigEndian)) {
        Array(UnsafeBufferPointer(start: $0, count: MemoryLayout.size(ofValue: bigEndian)))
    }
}

使用仅有效的指针($0)调用闭包在关闭的整个生命周期内，不得传递到外部供以后使用.这就是创建Array并将其用作返回值的原因.

The closures are invoked with pointers ($0) which are only valid for the lifetime of the closure and must not be passed to the outside for later use. That's why an Array is created and used as return value.

但是有一个更简单的解决方案:

There is a simpler solution however:

let bytes = withUnsafeBytes(of: &bigEndian) { Array($0) }

说明: withUnsafeBytes用UnsafeRawBufferPointer调用闭包来存储bigEndian变量. 由于UnsafeRawBufferPointer是UInt8的Sequence，因此需要一个数组可以使用Array($0)从中创建.

Explanation: withUnsafeBytes invokes the closure with a UnsafeRawBufferPointer to the storage of the bigEndian variable. Since UnsafeRawBufferPointer is a Sequence of UInt8, an array can be created from that with Array($0).

如何在Swift 3中将UInt16转换为UInt8?

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