Convert string to *uint64 in golang

Question

Assume there is a string holding the address of an uint64 type variable, can we parse this address back to an *uint64?

For example:

i := uint64(23473824)
ip := &i
str := fmt.Sprintf("%v", ip)

u, _ := strconv.ParseUint(str, 0, 64)

u is uint64. How to get pointer out of this value?

Playground link: https://play.golang.org/p/1KXFQcozRk

I don't understand golang, but is this page helpful (http://stackoverflow.com/questions/5367961/casting-from-one-pointer-to-pointer-type-to-another-in-golang-error)? It deals with casting pointers. — Jonny, Mar 10 '15 at 15:26
@Rambatino that's a great question, but let's just say I was on the dark side once. — ecem, Apr 16 '19 at 16:32

score 17 · Answer 1 · answered Apr 16 '20 at 18:44

17

It is as simple as:

number, err := strconv.ParseUint(string("90"), 10, 64)

then do some error checking, hope it helps.

answered Apr 16 '20 at 18:44

Eduardo A EDUARDO Fernandez Di

402
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1

this doesn't work if `uint` is a 32-bit type, so it won't work in 32-bit builds – phuclv Dec 05 '22 at 12:46

score 4 · Answer 2 · answered Mar 10 '15 at 15:34

4

You can do it with

 ip = (*uint64)(unsafe.Pointer(uintptr(u)))

playground link

Albeit I don't know what guarantees Go gives you about the validity of such a pointer, nor can I think of any use case where this code should be used..

answered Mar 10 '15 at 15:34

nos

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score 4 · Answer 3 · edited May 23 '17 at 12:22

Based on nos answer.

Although it is technically possible there are reasons not to trust the code you wrote. Garbage collection will use the memory you point to (with string).

Take a look at result of the following code.

package main

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

func produce() string {
    i := uint64(23473824)
    ip := &i
    str := fmt.Sprintf("%v", ip)
    fmt.Println(i, ip, str)
    return str
}

func main() {
    str := produce()

    for i := 0; i < 10; i++ {
         x := make([]int, 1024*1024)
         x[0] = i
    }        

    u, _ := strconv.ParseUint(str, 0, 64) 

    ip := (*uint64)(unsafe.Pointer(uintptr(u)))
    fmt.Println(ip,*ip, reflect.TypeOf(u)) // u is uint64, how to get pointer out of this value?
}

https://play.golang.org/p/85XOhsMTf3

Convert string to *uint64 in golang

3 Answers3