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我正在用 Swift 编写 MsgPack 解析器作为学习语言的一种方式。感觉不太适合这项任务,但我一直在进步。现在我遇到了一个我似乎无法说服它将 4 个字节转换为浮点数的块。

var bytes:Array<UInt8> = [0x9A, 0x99, 0x99, 0x41] //19.20000

var f:Float = 0

memccpy(&f, &bytes, 4, 4)

print(f)

在操场上,我得到:

致命错误:无法打开 Optional.None Playground 执行失败:错误:执行被中断,原因:EXC_BAD_INSTRUCTION(代码=EXC_I386_INVOP,子代码=0x0)。

任何想法接下来要尝试什么?

4

2 回答 2

14

放下。&_ 是一个数组。&bytesbytes

    var bytes:Array<UInt8> = [0x9A, 0x99, 0x99, 0x41] //19.20000

    var f:Float = 0.0

    memccpy(&f, bytes, 4, 4) // as per OP. memcpy(&f, bytes, 4) preferred

    println ("f=\(f)")// f=19.2000007629395

更新斯威夫特 3

memccpy似乎在 Swift 3 中不起作用。正如评论员所说,使用memcpy

import Foundation
var bytes:Array<UInt8> = [0x9A, 0x99, 0x99, 0x41] //19.20000

var f:Float = 0.0

/* Not in Swift 3
 memccpy(&f, bytes, 4, 4) // as per OP.

 print("f=\(f)")// f=19.2
 */

memcpy(&f, bytes, 4) /

print("f=\(f)")// f=19.2
于 2014-06-23T08:27:39.243 回答
3
public func parseInt32(bytes:[UInt8], offset:Int)->Int32{

    var pointer = UnsafePointer<UInt8>(bytes)
    pointer = pointer.advancedBy(offset)

    let iPointer =  UnsafePointer<Int32>(pointer)
    return iPointer.memory

}

public func parseFloat32(bytes:[UInt8], offset:Int)->Float32{
    var pointer = UnsafePointer<UInt8>(bytes)
    pointer = pointer.advancedBy(offset)

    let fPointer =  UnsafePointer<Float32>(pointer)
    return fPointer.memory

}
于 2015-10-05T02:53:54.697 回答