将指针保存到golang中的String数据结构中

Question

This question already has an answer here:

• Pointers golang from string 1 answer

I have a data structure that only accepts strings and I want to store pointers to another data structure.

Enssentially I can save the pointers as string as such:

ptr := fmt.Sprint(&data) // ptr is now something like : 0xc82000a308

then later on I want to get the stuff store at the ptr, is there a way to cast this ptr to a pointer type?

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Answer 1

Sure, you can do that using the unsafe package:

https://play.golang.org/p/Wd7hWn9Zsu

package main

import (
    "fmt"
    "strconv"
    "unsafe"
)

func main() {
    //Given:
    data := "Hello"
    ptrString := fmt.Sprintf("%d", &data)

    //Convert it to a uint64
    ptrInt, _ := strconv.ParseUint(ptrString, 10, 64)

    //They should match
    fmt.Printf("Address as String: %s as Int: %d
", ptrString, ptrInt)

    //Convert the integer to a uintptr type
    ptrVal := uintptr(ptrInt)

    //Convert the uintptr to a Pointer type
    ptr := unsafe.Pointer(ptrVal)

    //Get the string pointer by address
    stringPtr := (*string)(ptr)

    //Get the value at that pointer
    newData := *stringPtr

    //Got it:
    fmt.Println(newData)

    //Test
    if(stringPtr == &data && data == newData) {
        fmt.Println("successful round trip!")
    } else {
        fmt.Println("uhoh! Something went wrong...")
    }
}

However, keep in mind the various warnings on the unsafe package. For example:

"A uintptr is an integer, not a reference. Converting a Pointer to a uintptr creates an integer value with no pointer semantics. Even if a uintptr holds the address of some object, the garbage collector will not update that uintptr's value if the object moves, nor will that uintptr keep the object from being reclaimed." - https://golang.org/pkg/unsafe/#Pointer