Swift筆記之 UInt8 那些事

2021-10-08 14:40:11 字數 4624 閱讀 5676

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[uint8]是swift中的陣列型別，也是作用比較特殊的一種陣列型別, 常用於底層互動與記憶體操作與管理。如: 字串編譯碼, 充當位元組緩衝區等等

string有對應的直接從[uint8]或[int8]轉換成string的建構函式

/// "這是乙個字串" 的utf8編碼


let bytes:


[uint8]=


[232


,191


,153


,230


,152


,175


,228


,184


,128


,228


,184


,170


,229


,173


,151


,231


,172


,166


,228


,184


,178


]/// 轉換成字串


iflet msg =


string


(bytes: bytes, encoding:


.utf8)
string轉[uint8]或[int8]時需要借助中間角色data

let msg =


"這是乙個字串"


iflet data = msg.


data


(using:


.utf8)
這裡的轉換指的是使用同一塊記憶體位址

c語言指標型別

swift語言指標物件型別

char *

unsafemutablepointer

const char *

unsafepointer

unsigned char *

unsafemutablepointer

const unsigned char *

unsafepointer

void *

unsafemutablerawpointer

const void *

unsaferawpointer

這些帶有buffer的指標型別， 可以理解為對應的不帶buffer的指標型別加上了緩衝區大小, 比如:

unsafepointer對應 const int *, 表示僅有位址

那unsafebufferpointer對應 const int * 加 size, 表示該位址與記憶體大小所對應的一塊緩衝區

[uint8]->unsaferawbufferpointer->unsafebufferpointer->unsafepointer(int8同理)

/// 0. 原始位元組資料 8位元組


let buffer =


[uint8


](repeating:0,


count:8


)/// 1. [uint8] -> unsaferawbufferpointer


let unsaferawbufferpointer = buffer.withunsafebytes 


/// 2. unsaferawbufferpointer -> unsafebufferpointer


let unsafebufferpointer = unsaferawbufferpointer.


bindmemory


(to:


uint8


.self


)/// 3. unsafebufferpointer-> unsafepointer


let unsafepointer = unsafebufferpointer.baseaddress
其中步驟1和步驟2可以合併

/// 0. 原始位元組資料 8位元組


let buffer =


[uint8


](repeating:0,


count:8


)/// 1. [uint8] -> unsafebufferpointer


let unsafebufferpointer = buffer.withunsafebufferpointer 


/// 2.. unsafebufferpointer-> unsafepointer


let unsafepointer = unsafebufferpointer.baseaddress
[uint8]->unsafemutablerawbufferpointer->unsafemutablebufferpointer->unsafemutablepointer(int8同理)

/// 0. 原始位元組資料 8位元組


var buffer =


[uint8


](repeating:0,


count:8


)/// 1. [uint8] -> unsafemutablerawbufferpointer


let unsafemutablerawbufferpointer = buffer.withunsafemutablebytes 


/// 2. unsafemutablerawbufferpointer -> unsafemutablebufferpointer


let unsafemutablebufferpointer = unsafemutablerawbufferpointer.


bindmemory


(to:


uint8


.self


)/// 3. unsafemutablebufferpointer-> unsafemutablepointer


let unsafemutablepointer = unsafemutablebufferpointer.baseaddress
其中的步驟1和步驟2也是可以合併的

/// [uint8] -> unsafemutablebufferpointer


let unsafemutablebufferpointer = buffer.withunsafemutablebufferpointer
在上述的步驟裡, 在步驟1得到的unsafemutablerawbufferpointer就可以通過該物件的baseaddress欄位就能獲取到對應的void *如:

/// 獲取 const void *


let unsaferawpointer = unsaferawbufferpointer.baseaddress


/// 獲取void *


let unsafemutablerawpointer = unsafemutablerawbufferpointer.baseaddress
/// 這裡是示例， 型別為 unsafemutablepointer， 也就是 char *


/// message可能來自任何c語言的介面


let message =


strerror


(errno)


/// 通過指標和大小來構造 unsafebufferpointer


let unsafebufferpointer =


unsafebufferpointer


<


int8


>


(start: message,


count


:strlen


(msg!))


/// 構造data


let data =


data


(buffer: unsafebufferpointer)
但是如果需要拷貝出來乙份 [uint8]或者[int8]，可以使用map函式

/// 緩衝區裡的資料    


let data =


data


(buffer: unsafebufferpointer)


/// [uint8]


let u8a = data.


map/// [int8]


let s8a = data.


map
let text =


string


(data: data, encoding:


.utf8)

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