How do I convert []byte with zero values to string in Go?

Question

I know there are questions like this already: How do I convert [Size]byte to string in Go?, but my questions is "how do I convert []byte WITH ZERO VALUES to string"

package main

import (
    "fmt"
    "strings"
)

func main() {
    a := make([]byte, 16)

    r := strings.NewReader("test")
    _, _ = r.Read(a)

    b := "test"

    fmt.Println(string(a), b)
    fmt.Println(string(a) == b)
    fmt.Println(len(string(a)), len(b))
    fmt.Println(a, []byte(b))
}

The code above prints:

test test
false
16 4
[116 101 115 116 0 0 0 0 0 0 0 0 0 0 0 0] [116 101 115 116]

As you can see the zero values in a caused inequality between a and b, how should I treat them? How can I compare the two correctly?

Those are not empty. Zero is still a value. But if you want to remove trailing zeros, just make a slice of the appropriate length, using the same array as its backing store, using the slice operation: aShortened := a[:len]. (Note that the Read operation returns a length and you should probably save it rather than throwing it away. It also returns an error, which you should check.) — torek
– torek, Commented May 6, 2021 at 4:13
You probably should take the Tour of Go for basic language fundamentals like how slices work, what zero values are and how an io.Reader's Read method works. — Volker
– Volker, Commented May 6, 2021 at 4:40

junchaw · Accepted Answer · 2021-05-06 06:04:57Z

1

The length returned by Read helps to slice the array:

a := make([]byte, 16)

r := strings.NewReader("test")
l, _ = r.Read(a)

b := "test"

fmt.Println(string(a[:l]) == b)) // true, they are equal!

Thanks @torek

answered May 6, 2021 at 6:04

junchaw

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Comments

Matt · Accepted Answer · 2021-05-06 06:48:07Z

1

When you declare your slice a:

a := make([]byte, 16)

All of the elements are initialised with the "zero value" of a byte which is 0.

You can consider the slice full, for all intents and purposes. You are free to overwrite it in full, or partially, but it will always be a 16 element slice with a value at each index.

If you want to trim the zero values from the end of the slice, you could do that:

func trim(a []byte) []byte {
  for i := len(a) - 1; i >= 0; i-- {
    if a[i] != 0 {
      // found the first non-zero byte
      // return the slice from start to the index of the first non-zero byte
      return a[:i+1]
    }
  }

  // didn't find any non-zero bytes just return an empty slice
  return []byte{}
}

And then compare:

string(trim(a)) == b

edited May 6, 2021 at 6:48

answered May 6, 2021 at 4:13

Matt

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