在Swift中将NSData转换为Integer

Question

在Objective-C中,代码看起来很喜欢这个并且工作得很完美,

NSInteger random = arc4random_uniform(99) + 1 
NSData *data = [NSData dataWithBytes:& random length: sizeof(random)];
int value = *(int*)([data bytes]);

怎么能在Swift中完成？

Answer 1

像这样:

var src: NSInteger = 2525
var out: NSInteger = 0

let data = NSData(bytes: &src, length: sizeof(NSInteger))
data.getBytes(&out, length: sizeof(NSInteger))
println(out) // ==> 2525

Answer 2

在Swift 4中:

从Data流中提取整数值时,需要考虑几件事情.符号性和字节序.所以我在扩展中提出了一个函数,它从你想要提取的整数类型中Data推断出Signness,并传递Endianess和Index参数.可以提取的整数类型都符合FixedWidthInteger协议.

提醒:此函数不会检查Index范围是否在Data缓冲区的边界内,因此它可能会崩溃,具体取决于相对于缓冲区末端提取的类型的大小.

extension Data {
    enum Endianness {
        case BigEndian
        case LittleEndian
    }
    func scanValue<T: FixedWidthInteger>(at index: Data.Index, endianess: Endianness) -> T {
        let number: T = self.subdata(in: index..<index + MemoryLayout<T>.size).withUnsafeBytes({ $0.pointee })
        switch endianess {
        case .BigEndian:
            return number.bigEndian
        case .LittleEndian:
            return number.littleEndian
        }
    }
}

例:

let data = Data(bytes: [0xFF,0x1F,0x1F,0xFF])

let number1 = data.scanValue(at: 0, endianess: .LittleEndian) as UInt16
let number2 = data.scanValue(at: 0, endianess: .BigEndian) as UInt16

let number3: Int16 = data.scanValue(at: 2, endianess: .LittleEndian)
let number4: Int16 = data.scanValue(at: 2, endianess: .BigEndian)

结果:

number1 is 8191
number2 is 65311
number3 is -225
number4 is 8191

观察函数调用以查看如何推断要提取的类型.当然字节序没有意义的Int8或UInt8,但功能正常工作.

Int如果需要,稍后可以转换为值.

Answer 3

对于Swift 3,你可以这样做(小端,但类似于大):

func getInt(fromData data: Data, start: Int) -> Int32 {
  let intBits = data.withUnsafeBytes({(bytePointer: UnsafePointer<UInt8>) -> Int32 in
    bytePointer.advanced(by: start).withMemoryRebound(to: Int32.self, capacity: 4) { pointer in
      return pointer.pointee
    }
  })
  return Int32(littleEndian: intBits)
}

您可以修改它,添加泛型等以适应其他基本类型(并根据数据字节的字节顺序来改变它).

Answer 4

您可以根据需要扩展数据类型、创建泛型方法、获取字节并对其进行转换或显式设置结果类型：

extension Data {
    func object<T>(at index: Index = 0) -> T {
        subdata(in: index..<self.index(index, offsetBy: MemoryLayout<T>.size))
        .withUnsafeBytes { $0.load(as: T.self) }
    }
}

extension Numeric {
    var data: Data {
        var source = self
        return Data(bytes: &source, count: MemoryLayout<Self>.size)
    }
}

let data = Data([0xFF, 0x1F])   // 2 bytes

let uint16: UInt16 = data.object()      // 8191  littleEndian
let number1 = uint16.littleEndian       // 8191
let number2 = uint16.bigEndian          // 65311

let int16 = data.object() as Int16      // 8191   littleEndian
let number3 = int16.littleEndian        // 8191
let number4 = int16.bigEndian           // -225

print(number1) // 8191
print(number2) // 65311
print(number3) // 8191
print(number4) // -225

测试 Int

let random = Int.random(in: 1...100)    // 15 UInt32
let data = random.data                  // 8 bytes  [15, 0, 0, 0, 0, 0, 0, 0]

测试 UInt32

let random = UInt32.random(in: 1...100)  // 90 UInt32
let data = random.data                   // 4 bytes  [90, 0, 0, 0]

用双重测试

let random = Double.random(in: 0...1)  // 0.2463145485351322 Double
let data = random.data                 // 8 bytes  [12, 99, 62, 49, 60, 135, 207, 63]

如果要提取子数据：

let data = Data([0xFF, 0x1F, 0x1F, 0xFF])      // 4 bytes

let uint16: UInt16 = data.object(at: 2)        //  65311 littleEndian
let number1 = uint16.littleEndian              // 65311
let number2 = uint16.bigEndian                 // 8191

let int16: Int16 = data.object(at: 2)          // -225   littleEndian
let number3 = int16.littleEndian               // -225
let number4 = int16.bigEndian                  // 8191

number1 // 65311
number2 // 8191
number3 // -225
number4 // 8191

Answer 5

如果您经常这样做,您可能会发现此方法很有用:

func readInteger<T : IntegerType>(data : NSData, start : Int) -> T {
    var d : T = 0
    data.getBytes(&d, range: NSRange(location: start, length: sizeof(T)))
    return d
}

该函数将数据中的起始位置作为参数读取数字类型,并返回从您分配给它的任何内容推断出的类型的值.

例如:

let i : UInt32 = readInteger(data, 10);

从数据中的位置10读取4字节整数.

如果更改UInt32为UInt16它将读取两个字节.