英文:
How to store the address pointed to by a pointer?
问题
我正在尝试创建一个地址映射表，用于存储我使用new()创建的对象的地址和分配时间。键是通过调用new()返回的地址。如何获取new()返回的地址？
type T struct{a, b int }
func main(){
var t int64 = time.Nanoseconds()
memmap := make(map[uintptr]int64)
fmt.Printf("%d\n", t)
var ptr *T = new(T)
ptr.a = 1
ptr.b = 2
fmt.Printf("%d %d %p %T\n", ptr.a, ptr.b, ptr, ptr)
memmap[uintptr(unsafe.Pointer(ptr))] = t
}
请告诉我在映射表中键字段的类型应该是什么，以便我可以存储new()返回的地址？我计划使用不同类型的new()，获取分配的地址并将其与创建时间进行映射。
英文:
I am trying to create a map of addresses of objects that I create with the time at which it is allocated. The key is the address returned by the call to new(). How do I get the address returned by new()?
type T struct{a, b int }
func main(){
var t int64 = time.Nanoseconds()
memmap := make(map[uint8]int64)
fmt.Printf("%d\n", t)
var ptr *T = new(T)
ptr.a = 1
ptr.b = 2
fmt.Printf("%d %d %p %T\n", ptr.a, ptr.b, ptr, ptr)
//memmap[ptr] = t //gives error
//var temp uint8 = ptr//gives error
}
Please tell me what should be the type of the key field in the map so that I can store the address returned by new()? I plan to use new() with different types, get the allocated address and map it with the creation time.
答案1
得分: 7
你可以使用unsafe包中的Pointer类型，但是正如包名所暗示的那样，它是不安全的。地址本身是一个不透明的东西，实际上仅使用地址值本身来进行映射是很少有用的，最好使用类型和地址的元组。这就是unsafe.Reflect提供的功能。reflect包提供了UnsafeAddr函数和更多功能。
我建议你阅读reflect和unsafe包的文档。
英文:
You can use the type Pointer from the unsafe package, but that is, the package name implies it, unsafe. The address itself is a opaque thing and there's only little use in actually using a address value alone for a map, better use a tuple of type and address. That's what unsafe.Reflect does provide you. The package reflect offers you the function UnsafeAddr and a lot more.
I suggest you read the package documentation for reflect and unsafe packages.
答案2
得分: 3
使用uintptr，一个足够大的无符号整数来存储指针值的未解释位，作为内存映射的键类型。
例如，
package main
import (
"fmt"
"time"
"unsafe"
)
type T struct{ a, b int }
func main() {
memmap := make(map[uintptr]int64)
pT := new(T)
memmap[uintptr(unsafe.Pointer(pT))] = time.Nanoseconds()
pT.a = 1
pT.b = 2
fmt.Printf("%d %d %p %T\n", pT.a, pT.b, pT, pT)
pI := new(int)
memmap[uintptr(unsafe.Pointer(pI))] = time.Nanoseconds()
*pI = 42
fmt.Printf("%d %p %T\n", *pI, pI, pI)
fmt.Printf("\n%T\n", memmap)
for k, v := range memmap {
fmt.Printf("%x: %d\n", k, v)
}
}
输出：
1 2 0xf8400001f8 *main.T
42 0xf8400001f0 *int
map[uintptr] int64
f8400001f0: 1306837191421330000
f8400001f8: 1306837191421293000
英文:
Use uintptr, an unsigned integer large enough to store the uninterpreted bits of a pointer value, as the memory map key type.
For example,
package main
import (
"fmt"
"time"
"unsafe"
)
type T struct{ a, b int }
func main() {
memmap := make(map[uintptr]int64)
pT := new(T)
memmap[uintptr(unsafe.Pointer(pT))] = time.Nanoseconds()
pT.a = 1
pT.b = 2
fmt.Printf("%d %d %p %T\n", pT.a, pT.b, pT, pT)
pI := new(int)
memmap[uintptr(unsafe.Pointer(pI))] = time.Nanoseconds()
*pI = 42
fmt.Printf("%d %p %T\n", *pI, pI, pI)
fmt.Printf("\n%T\n", memmap)
for k, v := range memmap {
fmt.Printf("%x: %d\n", k, v)
}
}
Output:
1 2 0xf8400001f8 *main.T
42 0xf8400001f0 *int
map[uintptr] int64
f8400001f0: 1306837191421330000
f8400001f8: 1306837191421293000
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