Golang - unable to parse JSON

Question

I've started learning GO, and i have encountered this issue. I have this code

package main

import (
  "log"
  "encoding/json"
)


func main(){
  type Weather struct {
    name string
    cod float64
    dt float64
    id float64
  }

  var rawWeather = []byte(`{"name":"London","cod":200,"dt":1407100800,"id":2643743}`)
  var w Weather
  err := json.Unmarshal(rawWeather, &w)
  if err != nil {
    log.Fatalf("%s : while parsing json", err)
  }
  log.Printf("%+v\n",w)
}

when i run it, it shows this

[nap@rhel projects]$ go run euler.go 
{name: cod:0 dt:0 id:0}

So, the JSON is not parsed into the weather struct.

Any ideas, why do this happens like this?

Make the struct fields as exported.

Shudipta Sharma
– Shudipta Sharma

2021-10-03 15:06:44 +00:00
Commented Oct 3, 2021 at 15:06 — Shudipta Sharma
– Shudipta Sharma, Commented Oct 3, 2021 at 15:06

Simon Whitehead · Accepted Answer · 2014-08-03 23:06:15Z

7

You need to capitalise your struct fields. E.g:

Name string
Cod  float64
// etc..

This is because they are not visible to the json package when attempting to unmarshal.

Playground link: http://play.golang.org/p/cOJD4itfIS

answered Aug 3, 2014 at 23:06

Simon Whitehead

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Comments

evanmcdonnal · Accepted Answer · 2014-08-04 16:17:43Z

1

This is because Weather does not export any fields. This;

type Weather struct {
   name string
   cod float64
   dt float64
   id float64
}

Needs to be;

type Weather struct {
   Name string
   Cod float64
   Dt float64
   Id float64
}

If a field is not exported then the json package will not be able to access it. You can find more information about it here http://blog.golang.org/json-and-go but the short version is;

" The json package only accesses the exported fields of struct types (those that begin with an uppercase letter). Therefore only the the exported fields of a struct will be present in the JSON output."

answered Aug 4, 2014 at 16:17

evanmcdonnal

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Comments

vodolaz095 · Accepted Answer · 2014-08-03 23:03:02Z

0

By quessing, i found, that this code works:

package main

import (
  "fmt"
  "encoding/json"
//  "net/html"
)


func main(){
  type Weather struct {
    Name string
    Cod float64
    Dt float64
    Id float64
  }

  var rawWeather = []byte(`[{"name":"London","cod":200,"dt":1407100800,"id":2643743}]`)
  var w []Weather
  err := json.Unmarshal(rawWeather, &w)
  if err != nil {
    fmt.Println("Some error", err)
  }
  fmt.Printf("%+v\n",w)
}

So, the struct field names have to be Capitalized to work properly!

answered Aug 3, 2014 at 23:03

vodolaz095

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2 Comments

ilpaijin Over a year ago

Capitalizing its properties means give them a "public visibility" in an instance scope, I suppose... Am I wrong or sounds weird a struct defined inside the main function?

Shudipta Sharma Over a year ago

@ilpaijin please see this stackoverflow.com/questions/31380268/…

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