swift指針及內(nèi)存管理內(nèi)存綁定實(shí)例詳解

更新時(shí)間：2022年11月24日 11:35:01 作者：i_erlich

這篇文章主要為大家介紹了swift指針及內(nèi)存管理內(nèi)存綁定實(shí)例詳解，有需要的朋友可以借鑒參考下，希望能夠有所幫助，祝大家多多進(jìn)步，早日升職加薪

swift API 綁定

swift提供了3種不同的API來(lái)綁定/重新綁定指針

assumingMemoryBound(to:)
bindMemory(to: capacity:)
withMemoryRebound(to: capacity: body:)

繞過(guò)編譯器檢查 - assumingMemoryBound

就是假定內(nèi)存綁定

func testPointer(_ p: UnsafePointer<Int>) {
    print(p)
}
let tuple = (30, 40)
withUnsafePointer(to: tuple) { (tuplePtr: UnsafePointer<(Int, Int)>) in
    testPointer(UnsafeRawPointer(tuplePtr)
    .assumingMemoryBound(to: Int.self))
}

其實(shí) 兩者本質(zhì)沒(méi)什么區(qū)別，都是指向內(nèi)存的指針

UnsafePointer 指向1塊Int內(nèi)存

UnsafePointer<Int, Int> 指向一個(gè)元組tuple內(nèi)存, 也就是一塊連續(xù)的內(nèi)存，包含連個(gè)連續(xù)的Int

兩者都是首地址

一種方式就是不強(qiáng)轉(zhuǎn) UnsafePointer<Int, Int> 為 UnsafePointer

先把元組指針轉(zhuǎn)換成原始指針 UnsafeRawPointer(tuplePtr)
原始指針調(diào)用 assumingMemoryBound 綁定成Int 指針 UnsafeRawPointer(tuplePtr).assumingMemoryBound(to: Int.self)

func testPointer(_ p: UnsafePointer<Int>) {
    print(p[0])
    print(p[1])
}
let tuple = (30, 40)
withUnsafePointer(to: tuple) { (tuplePtr: UnsafePointer<(Int, Int)>) in
    testPointer(UnsafeRawPointer(tuplePtr).assumingMemoryBound(to: Int.self))
}

結(jié)果

30

40

assumingMemoryBound的意義在于：

有時(shí)候不想做指針類型轉(zhuǎn)換來(lái)增加代碼的復(fù)雜度

就可以調(diào)用此api繞過(guò)編譯器檢查，但是并沒(méi)有發(fā)生實(shí)際的指針轉(zhuǎn)換

內(nèi)存轉(zhuǎn)換 - bindMemory

實(shí)際發(fā)生了轉(zhuǎn)換，改變當(dāng)前內(nèi)存指針綁定的類型

func testPointer(_ p: UnsafePointer<Int>) {
    print(p[0])
    print(p[1])
}
let tuple = (30, 40)
withUnsafePointer(to: tuple) { (tuplePtr: UnsafePointer<(Int, Int)>) in
    testPointer(UnsafeRawPointer(tuplePtr)
    .bindMemory(to: Int.self, capacity: 1))
}

結(jié)果

30

40

bindMemory - 相比于assumingMemoryBound，就是改變內(nèi)存綁定類型

臨時(shí)改變內(nèi)存綁定 - withMemoryRebound

func testPointer(_ p: UnsafePointer<Int8>) {
    print(p)
}
let UInt8Ptr = UnsafePointer<UInt8>.init(bitPattern: 30)
UInt8Ptr?.withMemoryRebound(to: Int8.self, capacity: 1, 
	{ (Int8Ptr: UnsafePointer<Int8>) in
    testPointer(Int8Ptr)
})

結(jié)果