CODEWITHSUNDEEP
stringpointersgouint64
ecem
ecem

Reputation: 3614

Convert string to *uint64 in golang

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

Upvotes: 15

Views: 37032

Answers (3)

Eduardo A EDUARDO Fernandez Di
Eduardo A EDUARDO Fernandez Di

Reputation: 438

It is as simple as:

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

then do some error checking, hope it helps.

Upvotes: 19

Grzegorz Żur
Grzegorz Żur

Reputation: 49231

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

Upvotes: 4

nos
nos

Reputation: 229264

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..

Upvotes: 4

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