[英]golang copy pointer value from pointer type slice
type Order struct {
*Res
Status int
}
type Res struct {
ResID int64
OtaBookID string
StayDetail []*ResElement
TotalCharge float64
CustFName string
CustLName string
CreateTime time.Time
}
type ResElement struct {
Res *Res
OtaEleID string
OtaRoomID string
RoomID int
Arrival time.Time
Depart time.Time
Charge float64
CreateTime time.Time
}
I have a slice named orderList to record orders. 我有一个名为orderList的切片来记录订单。 Now i have the first order which OtaBookID is "A123", and i want to copy this order and change its OtaBookID to "B123". 现在,我具有OtaBookID为“ A123”的第一笔订单,并且我想复制此订单并将其OtaBookID更改为“ B123”。 The ResElement type have some other detail info to record this order and i hide them because it not affect my question. ResElement类型还有其他一些详细信息来记录此顺序,我将它们隐藏了,因为它不影响我的问题。 I can success change Res.OtaBookID but i have no idea how to change Res.StayDetail[0].Res.OtaBookID 我可以成功更改Res.OtaBookID,但是我不知道如何更改Res.StayDetail [0] .Res.OtaBookID
func main() {
var orderList []*Order
res := new(Res)
res.OtaBookID = "A123"
resElt := new(ResElement)
resElt.Res = res
res.StayDetail = append(res.StayDetail, resElt)
order := new(Order)
order.Res = res
orderList = append(orderList, order)
originalOrder := new(Order)
originalOrder.Res = new(Res)
*originalOrder.Res = *order.Res
//originalOrder.Res.StayDetail[0].Res.OtaBookID = "B123" //this will make all become "B123"
originalOrder.Res.OtaBookID = "B123"
orderList = append(orderList, originalOrder)
fmt.Println(orderList[0].Res.OtaBookID) //A123
fmt.Println(orderList[1].Res.OtaBookID) //B123
fmt.Println(orderList[0].Res.StayDetail[0].Res.OtaBookID) //A123
fmt.Println(orderList[1].Res.StayDetail[0].Res.OtaBookID) //A123, i want this become B123
}
The result i want is orderList[0].Res.OtaBookID and orderList[0].Res.StayDetail[0].Res.OtaBookID is "A123" and other is "B123" 我想要的结果是orderList [0] .Res.OtaBookID和orderList [0] .Res.StayDetail [0] .Res.OtaBookID是“ A123”,其他是“ B123”
ps: Because i'm taking over other's works. ps:因为我要接管别人的作品。 So the three type already fixed and can not adjust. 因此这三种类型已经固定并且无法调整。 I want to know in this situation whether have any method to arrive my goal 我想知道在这种情况下是否有任何方法可以达到我的目标
From your example and clarification we can focus on main to achieve your goal: 从您的示例和说明中,我们可以专注于主要实现您的目标:
type Order struct {
*Res
Status int
}
type Res struct {
ResID int64
OtaBookID string
StayDetail []*ResElement
TotalCharge float64
CustFName string
CustLName string
CreateTime time.Time
}
type ResElement struct {
Res *Res
OtaEleID string
OtaRoomID string
RoomID int
Arrival time.Time
Depart time.Time
Charge float64
CreateTime time.Time
}
func main() {
var orderList []*Order
res := new(Res)
res.OtaBookID = "A123"
resElt := new(ResElement)
resElt.Res = res
res.StayDetail = append(res.StayDetail, resElt)
order := new(Order)
order.Res = res
orderList = append(orderList, order)
originalOrder := new(Order)
originalOrder.Res = new(Res)
// The following statement will copy the values in the memory space of order to the memory
// space of originalOrder, but take note that a pointer contains a memory address. Thus,
// following this statement originalOrder.Res.StayDetail will point to the same address
// as order.Res.StayDetail as slices are pointers...
*originalOrder.Res = *order.Res
// We now have to manually copy the slice to ensure it is different from the one in order.
// We must create a new slice to avoid overwriting the source.
originalOrder.Res.StayDetail := make([]*ResElement, len(order.Res.StayDetail))
// Further, this slice contains pointers so we must copy these as well to ensure they do not
// point to the ResElements of order.
for i, v := range order.Res.StayDetail {
re := new(ResElement)
// copy the values of the memory in v to the values in the memory of re
*re = *v
// set re.Res to point to originalOrder.Res as it currently point to order.Res
re.Res = originalOrder.Res
// Now we must place re in the slice of originalOrder as it currently points to an
// empty array of the correct size. Thus, we will not use append (which will grow
// the size), we will just set the index to the correct value. Thus:
originalOrder.StayDetail[i] = re
}
// The pointers and structures have now been properly set up, thus the following are equivalent:
// originalOrder.OtaBookID = "B123" - Res via embedding
// originalOrder.Res.OtaBookID = "B123" - Res directly
// originalOrder.Res.StayDetail[0].Res.OtaBookID = "B123" - Res via ResElement pointer Res
// They all point to the exact same memory space
originalOrder.Res.OtaBookID = "B123"
orderList = append(orderList, originalOrder)
fmt.Println(orderList[0].Res.OtaBookID) //A123
fmt.Println(orderList[1].Res.OtaBookID) //B123
fmt.Println(orderList[0].Res.StayDetail[0].Res.OtaBookID) //A123
fmt.Println(orderList[1].Res.StayDetail[0].Res.OtaBookID) //B123
}
Always remember that a pointer is just a memory address. 永远记住,指针只是一个内存地址。 If the address value is 0xffab67e1 a copy of the pointer will also contain the same value of 0xffab67e1 and effectively point to the same thing. 如果地址值为0xffab67e1,则指针的副本也将包含相同的值0xffab67e1,并有效地指向同一对象。 Thus you must deliberately assign new memory space at a new address and copy the internal values. 因此,您必须故意在新地址处分配新的内存空间,并复制内部值。 This must be done for any structures that contain pointers. 必须对任何包含指针的结构执行此操作。 We call this a Deep Copy or a Clone. 我们称其为深拷贝或克隆。
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