Swift指针

Swift指针为结构体表示分为两种，一种是带有格式的，一种是不带格式的。

如：

UnsafePointer这种是带格式的，带格式的指针实现了Pointee，所以可以使用.pointee来取值；

UnsafeRawPointer这种是不带格式的 ，可以理解为一段的纯粹的二进制，要对UnsafeRawPointer这种指针取值，需要将其转化为带格式的指针。

带有mutale的为值可变指针，即可以对指针对应的值赋值，不带的mutale的为只读指针

指针初始化
注意：使用alloc初始化的指针，释放的时候都要调用deallocate来释放

方法一:

var str = "test"

let pointer = withUnsafePointer(to: &str, {

      return $0

})

得到的是一个UnsafePointer

方法二：

let pointer = UnsafeMutablePointer.allocate(capacity: 8)

得到的是一段长度为8个字节的指针UnsafeMutablePointer

如果要得到一个空指针怎么办呢？

在oc中我们通常会用：(float *)NULL来表示

swift 提供了类似的函数使用：UnsafePointer(bitPattern: 0)

方法三：

先初始化无格式指针，再将无格式指针转化为有格式指针

let rawPointer = calloc(8, MemoryLayout<UInt8>.size)!

let pointer = rawPointer.assumingMemoryBound(to: UInt32)

方法四：

使用&,只能用于函数传递，例如：

var testStr = "test"

test(&testStr)

print(testStr)

func test(_ pointer: UnsafeMutablePointer) {

      pointer.pointee = "changed"

}

指针类型变化

如果我有一个UnsafeMutablePointer<UInt8>想按照UnsafeMutablePointer<UInt32>读取怎么办？

let point = UnsafeMutablePointer<UInt8>.allocate(capacity: 8)

 let newPointer = point.withMemoryRebound(to: UInt32, capacity: 2, {

       return $0

  })

赋值和取值

        var testStr = "123456789"

        let testP = withUnsafeMutablePointer(to: &testStr, {

            return $0

        })

        print(testP.pointee)

        testP.pointee = "abcdefg"

        print(testP)

data与bytes

        let str = "aaaaaaabbbbbbbccccccc"

        var data = str.data(using: .utf8)!

        data.withUnsafeMutableBytes { (bytes: UnsafeMutablePointer) -> Void in

            var bytesStart = bytes

            for _ in 0..

                print(bytesStart.pointee)

                bytesStart += 1

            }

        }

UnsafeBufferPointer（类似于bytes），用法与UnsafePointer差不多，实现了Sequence

        let str = "aaaaaaabbbbbbbccccccc"

        var data = str.data(using: .utf8)!

        let pointer = UnsafeMutableBufferPointer.allocate(capacity: data.count)

        data.copyBytes(to: pointer)

        for i in 0..10

            print(pointer[i])

        }