How do I iterate over a JSON array in Golang?

Question

I am trying to decode a JSON array and put it in a slice of a struct. I've read how to do this, but only if the JSON array contains keys. My JSON array does not contain keys.

I have stripped the program down to only the part where it handles the JSON data. It compiles and can be found below.

package main

// 2014-04-19

import (
    "fmt"
    "encoding/json"
)

type itemdata struct {
    data1 int // I have tried making these strings
    data2 int
    data3 int
}

func main() {
    datas := []itemdata{}

    json.Unmarshal([]byte(`[["7293","1434","99646"],["4657","1051","23795"]]`), &datas)
    // I have tried the JSON string without the qoutes around the numbers
    fmt.Println(len(datas)) // This prints '2'
    fmt.Println("This prints") // This does print 
    for i := range datas {
        fmt.Println(datas[i].data1)  // This prints '0', two times 
    }
    fmt.Println("And so does this") // This does print
}

I've searched for things like 'Go Lang JSON decode without keys' and read articles (and 'package pages') on the Go Lang website. I can find enough information on how to work with Go and JSON, but none of my found articles explain how to do it without keys in the JSON array.

I wouldn't find it odd if I would get an error; The JSON values are stringy-numbers (that's how I get them as input), but I am trying to put them in integers. I am not getting an error though. I have tried making the values in the 'itemdata' struct strings, that didn't help much. Removing the quotes from the JSON values didn't help either.

I would like to know how I can make my JSON array in a slice of 'itemdata'. The first out of three values would go into 'itemdata.data1', the second in 'itemdata.data2' and the third in 'itemdata.data3'.

Please let me know if you think I can improve my question.

Thanks in advance,
Remi

Answer 1

What you have here is a bi-dimensional array of strings. You can decode it like this :

type itemdata [][]string

func main() {
   var datas itemdata

    json.Unmarshal([]byte(`[["7293","1434","99646"],["4657","1051","23795"]]`), &datas)
    fmt.Println(len(datas))
    fmt.Println("This prints")
    for i := range datas {
        fmt.Println(datas[i][1]) 
    }
    fmt.Println("And so does this")
}

Demonstration