How to parse JSON array in Go

Question

How to parse a string (which is an array) in Go using json package?

type JsonType struct{     Array []string }  func main(){     dataJson = `["1","2","3"]`     arr := JsonType{}     unmarshaled := json.Unmarshal([]byte(dataJson), &arr.Array)     log.Printf("Unmarshaled: %v", unmarshaled) } 

Answer 1

The return value of Unmarshal is an error, and this is what you are printing out:

// Return value type of Unmarshal is error. err := json.Unmarshal([]byte(dataJson), &arr) 

You can get rid of the JsonType as well and just use a slice:

package main  import (     "encoding/json"     "log" )  func main() {     dataJson := `["1","2","3"]`     var arr []string     _ = json.Unmarshal([]byte(dataJson), &arr)     log.Printf("Unmarshaled: %v", arr) }  // prints out: // 2009/11/10 23:00:00 Unmarshaled: [1 2 3] 

Code on play: https://play.golang.org/p/GNWlylavam

Background: Passing in a pointer allows Unmarshal to reduce (or get entirely rid of) memory allocations. Also, in a processing context, the caller may reuse the same value to repeatedly - saving allocations as well.

Answer 2

Note: This answer was written before the question was edited. In the original question &arr was passed to json.Unmarshal():

unmarshaled := json.Unmarshal([]byte(dataJson), &arr) 

---

You pass the address of arr to json.Unmarshal() to unmarshal a JSON array, but arr is not an array (or slice), it is a struct value.

Arrays can be unmarshaled into Go arrays or slices. So pass arr.Array:

dataJson := `["1","2","3"]` arr := JsonType{} err := json.Unmarshal([]byte(dataJson), &arr.Array) log.Printf("Unmarshaled: %v, error: %v", arr.Array, err) 

Output (try it on the Go Playground):

2009/11/10 23:00:00 Unmarshaled: [1 2 3], error: <nil> 

Of course you don't even need the JsonType wrapper, just use a simple []string slice:

dataJson := `["1","2","3"]` var s []string err := json.Unmarshal([]byte(dataJson), &s)