swift - 在 Swift 3 中将 C 数组 ptr 转换为 native 数组

Question

我有一个来自 C 库的指向 float 数组的指针。它的类型是 UnsafeMutablePointer。如何在 Swift 3 中由此创建原生 [Float] 数组？

这是我正在尝试的:

var reconstructedFloats = [Float](repeatElement(0, count: size))
reconstructedFloats.withUnsafeMutableBufferPointer {
  let reconstructedFloatsPtr = $0
  print(type(of:$0)) // "UnsafeMutableBufferPointer<Float>"
  cFloatArrayPtr?.withMemoryRebound(to: [Float].self, capacity: size) {
    UnsafeMutableRawPointer(reconstructedFloatsPtr.baseAddress!).storeBytes(of: $0.pointee, as: Float.self)
  }

UnsafeMutableRawPointer(reconstructedFloatsPtr.baseAddress!).storeBytes(of: (cFloatArrayPtr?.pointee)!, as: Float.self)
}

这看起来过于复杂，所以希望有一个简单的方法，但即使是这段代码也会产生编译错误:Type of expression is ambiguous without more context。

如果您想将其插入 Playground ，这里有一个设计 cFloatArrayPtr 的完整示例:

// Let's contrive a C array ptr:
var size = 3
var someFloats: [Float] = [0.1, 0.2, 0.3]
var cFloatArrayPtr: UnsafeMutablePointer<Float>?

someFloats.withUnsafeMutableBufferPointer {
    cFloatArrayPtr = $0.baseAddress
}

print(type(of:cFloatArrayPtr!)) // "UnsafeMutablePointer<Float>"

var reconstructedFloats = [Float](repeatElement(0, count: size))
reconstructedFloats.withUnsafeMutableBufferPointer {
    let reconstructedFloatsPtr = $0
    print(type(of:$0))
    cFloatArrayPtr?.withMemoryRebound(to: [Float].self, capacity: size) {
        UnsafeMutableRawPointer(reconstructedFloatsPtr.baseAddress!).storeBytes(of: $0.pointee, as: Float.self)
    }

    UnsafeMutableRawPointer(reconstructedFloatsPtr.baseAddress!).storeBytes(of: (cFloatArrayPtr?.pointee)!, as: Float.self)
}

print(reconstructedFloats)

Answer 1

您可以从您的指针创建一个UnsafeBufferPointer。 UnsafeBufferPointer 是一个Sequence，因此您可以直接从中创建一个数组:

let buffer = UnsafeBufferPointer(start: cFloatArrayPtr, count: size)
var reconstructedFloats = Array(buffer)

当然，这会创建一个副本。