指针

• Swift中也有专门的指针类型,这些都被定性为Unsafe不安全的,常见的又一下四种类型
  1.UnsafePonter<Pointee>类似于const Pointee
  2.UnsafeMutablePointer<Pointee>类似于Pointee *
  3.UnsafeRawPointer类似于const void *
  4.UnsafeMutableRawPointer类似于void *

var age = 10
func test1 (_ ptr: UnsafeMutablePointer<Int>){
    ptr.pointee += 10
    print(ptr.pointee)
}

func test2(_ ptr: UnsafePointer<Int>) {
    print(ptr.pointee)
}
test1(&age)//20
test2(&age)//20
print(age)//20

var age = 10
func test3(_ ptr: UnsafeMutableRawPointer) {
    ptr.storeBytes(of: 20, as: Int.self)
}

func test4(_ ptr: UnsafeRawPointer) {
    print(ptr.load(as: Int.self))
}
test3(&age)
test4(&age)//20
print(age)//20

• 指针的应用示例

import Foundation

var arr = NSArray(objects: 11,22,33,44)
arr.enumerateObjects { (obj, idx, stop) in
    print(idx,obj)
    
    if idx == 2 {//下标为2就停止遍历
        stop.pointee = true
    }
}
/* 打印结果
 0 11
 1 22
 2 33
 */
var arr1 = NSArray(objects: 11,22,33,44)
for (idx, obj) in arr1.enumerated() {
    print(idx,obj)
    if idx == 2 {
        break
    }
}
/* 打印结果
 0 11
 1 22
 2 33
 */

• 获得指向某个变量的指针

var age = 11
var ptr1 = withUnsafeMutablePointer(to: &age) { $0 }

var ptr2 = withUnsafePointer(to: &age, { $0 })

ptr1.pointee = 22
print(ptr2.pointee)//2
print(age)//22

var ptr3 = withUnsafeMutablePointer(to: &age) { UnsafeMutableRawPointer($0)}

var ptr4 = withUnsafePointer(to: &age) { UnsafeRawPointer($0)
}

ptr3.storeBytes(of: 33, as: Int.self)
print(ptr4.load(as: Int.self))//33
print(age)//33

• 获得指向堆空间实例的指针

class Person { }
var person = Person()
var ptr = withUnsafePointer(to: &person) { UnsafeRawPointer($0)
}

var heapPtr = UnsafeRawPointer(bitPattern: ptr.load(as: UInt.self))
print(ptr)//0x00000001000021c0 全局区的指针
print(heapPtr!)//0x0000000100508610 堆区指针

• 创建指针

import Foundation
var ptr = UnsafeRawPointer(bitPattern: 0x0000000100508610)

//创建
var ptr = malloc(16)
//存
ptr?.storeBytes(of: 11, as: Int.self)
ptr?.storeBytes(of: 22, toByteOffset: 8, as: Int.self)
//取
print((ptr?.load(as: Int.self))!)//11
print((ptr?.load(fromByteOffset: 8, as: Int.self))!)//22
//销毁
free(ptr)

var ptr = UnsafeMutableRawPointer.allocate(byteCount: 16, alignment: 1)
ptr.storeBytes(of: 11, as: Int.self)
ptr.advanced(by: 8).storeBytes(of: 22, as: Int.self)
print(ptr.load(as: Int.self))//11
print(ptr.advanced(by: 8).load(as: Int.self))//22
ptr.deallocate()

var ptr = UnsafeMutablePointer<Int>.allocate(capacity: 3)
ptr.initialize(to: 11)
ptr.successor().initialize(to: 32)
ptr.successor().successor().initialize(to: 33)
print(ptr.pointee)//11
print((ptr + 1).pointee)//22
print((ptr + 2).pointee)//33
print(ptr[0])//11
print(ptr[1])//22
print(ptr[2])//33
ptr.deinitialize(count: 3)
ptr.deallocate()

class Person {
    var age: Int
    var name: String
    init(age: Int, name: String) {
        self.age = age
        self.name = name
    }
    deinit {
        print(name,"deinit")
    }
}

var ptr = UnsafeMutablePointer<Person>.allocate(capacity: 3)
ptr.initialize(to: Person(age: 10, name: "Jack"))
(ptr + 1).initialize(to: Person(age: 11, name: "Rose"))
(ptr + 2).initialize(to: Person(age: 12, name: "Kate"))
//Jack deinit
//Rose deinit
//Kate deinit
ptr.deinitialize(count: 3)
ptr.deallocate()

• 指针之间的转换

var ptr = UnsafeMutableRawPointer.allocate(byteCount: 16, alignment: 1)
ptr.assumingMemoryBound(to: Int.self).pointee = 11
(ptr + 8).assumingMemoryBound(to: Double.self).pointee = 22.0
print(unsafeBitCast(ptr, to: UnsafePointer<Int>.self).pointee)//11
print(unsafeBitCast(ptr + 8, to: UnsafePointer<Double>.self).pointee)//22.0

ptr.deallocate()

• unsafeBitCast是忽略数据类型的强制转换,不会因为数据类型的变化而改编原来的内存数据
• 类似C++中的reinterpret_cast

class Person { }
var person = Person()
var ptr = unsafeBitCast(person, to: UnsafeRawPointer.self)
print(ptr)//0x0000000100508b80