指针分类
使用swift提供指针类型：
- UnsafePointer
- UnsafeMutablePointer
- UnsafeRawPointer
- UnsafeMutableRawPointer
UnsafePointer / UnsafeMutablePointer用法：
使用 pointee 属性可以进行读写操作;
var age = 10
func change1(_ ptr: UnsafeMutablePointer<Int>) {
ptr.pointee += 20
}
func change2(_ ptr: UnsafePointer<Int>) {
print(ptr.pointee)
}
change1(&age)
change2(&age) // 30
print(age) // 30
UnsafeRawPointer / UnsafeMutableRawPointer
var age = 10
func change3(_ ptr: UnsafeMutableRawPointer) {
ptr.storeBytes(of: 20, as: Int.self)
}
func change4(_ ptr: UnsafeRawPointer) {
print(ptr.load(as: Int.self))
}
change3(&age)
change4(&age) // 20
print(age) // 20
获取堆空间地址
class Person {}
var person = Person()
//获取person指针的地址值
var ptr = withUnsafePointer(to: &person) { UnsafeRawPointer($0) }
// 获取person指针的指向的地址，就是为Person的堆空间地址
var headPtr = UnsafeRawPointer(bitPattern: ptr.load(as: UInt.self))
print(ptr)
print(headPtr)
print(person)
0x00000001000031f8
0x00000001006b6340
- withUnsafePointer 的闭包返回类型就是person变量指针的地址值（栈空间）；
- headPtr 是获取 ptr指向的地址值，就是Person实例对象的地址（堆空间）；
创建 UnsafeRawPointer / UnsafeMutableRawPointer 创建指针
- 方式一：通过地址值创建
var ptr = UnsafeRawPointer(bitPattern: 0x0000000100003008)
- 方式二：
var ptr = malloc(16) // UnsafeMutableRawPointer
ptr?.storeBytes(of: 10, as: Int.self) // 8字节
ptr?.storeBytes(of: 20, toByteOffset: 8, as: Int.self) // 存放在后8字节中
print( (ptr?.load(as: Int.self))! ) // 10
print( (ptr?.load(fromByteOffset: 8, as: Int.self))! ) // 20
free(ptr)
- 方式三：
var ptr = UnsafeMutableRawPointer.allocate(byteCount: 16, alignment: 1)
ptr.storeBytes(of: 10, as: Int.self)
//ptr.advanced(by: 8).storeBytes(of: 20, as: Int.self)
(ptr + 8).storeBytes(of: 20, as: Int.self)
print( ptr.load(as: Int.self) ) // 10
print( ptr.load(fromByteOffset: 8, as: Int.self) ) // 20
print( ptr.advanced(by: 8).load(as: Int.self) ) // 20
print( (ptr + 8).load(as: Int.self) ) //20
ptr.deallocate()
fromByteOffset 与 advanced都能让指针进行偏移；创建指针后，记得释放；
UnsafePointer / UnsafeMutablePointer 创建指针
var ptr = UnsafeMutablePointer<Int>.allocate(capacity: 3)
ptr.initialize(to: 10)
ptr.successor().initialize(to: 20)
ptr.successor().successor().initialize(to: 30)
print(ptr.pointee) // 10
print(ptr.successor().pointee) // 20
print(ptr.successor().successor().pointee) // 30
ptr.deinitialize(count: 3)
ptr.deallocate()
或者：
var ptr = UnsafeMutablePointer<Int>.allocate(capacity: 3)
ptr.initialize(to: 10)
(ptr + 1).initialize(to: 20)
(ptr + 2).initialize(to: 30)
print(ptr.pointee) // 10
print((ptr + 1).pointee) // 20
print((ptr + 2).pointee) // 30
ptr.deinitialize(count: 3)
ptr.deallocate()
ptr表示创建3个整形的指针；initialize为初始化；successor表示每次偏移8字节（整形）；
指针之间的转换
var ptr = UnsafeMutableRawPointer.allocate(byteCount: 16, alignment: 1)
// assumingMemoryBound 返回 UnsafeMutablePointer<T>类型
ptr.assumingMemoryBound(to: Int.self).pointee = 10
(ptr + 8).assumingMemoryBound(to: Int.self).pointee = 20
print( unsafeBitCast(ptr, to: UnsafePointer<Int>.self).pointee ) // 10
print( unsafeBitCast(ptr + 8, to: UnsafePointer<Int>.self).pointee ) // 20
ptr.deallocate()
- unsafeBitCast 忽略数据类型的强制转换，不会因为数据类型的变化而改变原来的内存结构；
总结
- 以上都是使用整形存储在指针中，实际上存储对象，结构体等；
- UnsafeMutableRawPointer指针+1表示一个字节；UnsafeMutablePointer+1表示泛型对象占用内存字节数+1，即下一个对象；
源代码demo
