How to unmarshal objects inside array - arrays

Question

I am trying to get access to object's values inside of array
[
{
"name": "London",
"lat": 51.5073219,
"lon": -0.1276474,
"country": "GB",
"state": "England"
}
]
I use this code to unmarshal it
content, err := ioutil.ReadAll(res.Body)
if err != nil {
log.Fatal(err)
}
var data []ResponseData
err = json.Unmarshal(content, &data)
if err != nil {
log.Fatal(err)
}
This is my struct
type ResponseData struct {
Name string `json:"name"`
Lat float32 `json:"lat"`
Lon float32 `json:"lon"`
Country string `json:"country"`
State string `json:"state"`
}
I need to simply fmt.Println(data.Lat, data.Lon) later.

Answer 1

The code you presented should unmarshal your JSON successfully; the issue is with the way you are trying to use the result. You say you want to use fmt.Println(data.Lat, data.Lon) but this will not work because data is a slice ([]ResponseData) not a ResponseData. You could use fmt.Println(data[0].Lat, data[0].Lon) (after checking the number of elements!) or iterate through the elements.
The below might help you experiment (playground - this contains a little more content than below):
package main
import (
"encoding/json"
"fmt"
"log"
)
const rawJSON = `[
{
"name": "London",
"lat": 51.5073219,
"lon": -0.1276474,
"country": "GB",
"state": "England"
}
]`
type ResponseData struct {
Name string `json:"name"`
Lat float32 `json:"lat"`
Lon float32 `json:"lon"`
Country string `json:"country"`
State string `json:"state"`
}
func main() {
var data []ResponseData
err := json.Unmarshal([]byte(rawJSON), &data)
if err != nil {
log.Fatal(err)
}
if len(data) == 1 { // Would also work for 2+ but then you are throwing data away...
fmt.Println("test1", data[0].Lat, data[0].Lon)
}
for _, e := range data {
fmt.Println("test2", e.Lat, e.Lon)
}
}