如何将字节转换为浮点值在swift中? [英] How to convert bytes to a float value in swift?
问题描述
static func returnFloatValue(mutableData:NSMutableData) - > Float
{
let qtyRange = mutableData.subdataWithRange(NSMakeRange(0,4))
let qtyString = String(qtyRange)
let qtyTrimString = qtyString.stringByTrimmingCharactersInSet(NSCharacterSet(charactersInString: <>)
let qtyValue = Float(strtoul(qtyTrimString,nil,16)/ 10)
return qtyValue
}
谢谢
< 44fa0000>
是
二进制浮点数 2000.0
的big-endian 内存表示。要从
数据中获得数字,首先必须将其读入 UInt32
,然后从
big-endian转换为主机字节顺序,然后将结果转换为
a Float
。
在 Swift 2 将会是
pre $ func floatValueFromData(data:NSData) - >浮动{
返回unsafeBitCast(UInt32(bigEndian:UnsafePointer(data.bytes).memory),Float.self)
}
示例:
let bytes:[UInt8] = [0x44,0xFA,0x00 ,0x00]
let data = NSData(bytes:bytes,length:4)
print(data)//< 44fa0000>
let f = floatValueFromData(data)
print(f)// 2000.0
在 Swift 3 中,您可以使用 Data
而不是 NSData
,
unsafeBitCast
可以被浮动(bitPattern:)
初始值设定项:
func floatValue(data:Data) - >浮动{
返回浮动(bitPattern:UInt32(bigEndian:data.withUnsafeBytes {$ 0.pointee}))
}
This is my code to convert byte data to float. I tried every answers given in this site. I am getting exponential value for this "<44fa0000>" byte data
static func returnFloatValue(mutableData:NSMutableData)->Float
{
let qtyRange = mutableData.subdataWithRange(NSMakeRange(0, 4))
let qtyString = String(qtyRange)
let qtyTrimString = qtyString.stringByTrimmingCharactersInSet(NSCharacterSet(charactersInString: "<>"))
let qtyValue = Float(strtoul(qtyTrimString, nil, 16)/10)
return qtyValue
}
Thanks
<44fa0000>
is the big-endian memory representation of the
binary floating point number 2000.0
. To get the number back from
the data, you have to read it into an UInt32
first, convert from
big-endian to host byteorder, and then cast the result to
a Float
.
In Swift 2 that would be
func floatValueFromData(data: NSData) -> Float {
return unsafeBitCast(UInt32(bigEndian: UnsafePointer(data.bytes).memory), Float.self)
}
Example:
let bytes: [UInt8] = [0x44, 0xFA, 0x00, 0x00]
let data = NSData(bytes: bytes, length: 4)
print(data) // <44fa0000>
let f = floatValueFromData(data)
print(f) // 2000.0
In Swift 3 you would use Data
instead of NSData
, and the
unsafeBitCast
can be replaced by the Float(bitPattern:)
initializer:
func floatValue(data: Data) -> Float {
return Float(bitPattern: UInt32(bigEndian: data.withUnsafeBytes { $0.pointee } ))
}
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