Golang : fmt.Println prints out empty data from struct



Tags : golang fmt-println struct json

Problem :

Your code compiled successfully and there is no error indicator whatsoever. However, during runtime, the fmt.Println function prints out empty data that you expected from a struct that suppose to have unmarshaled JSON data. What's going on?

For example :

 package main

 import "fmt"
 import "encoding/json"

 func main() {
  var v = []byte(`[
 {
 "name": "D***",
 "email": "D***@gmail.com"
 "gender": "Male",
 "age": 27,
 }
 {
 "name": "A***",
 "email": "a@a.com"
 "gender": "Female",
 "age": 31,
 }
 ]`)
  type Person struct {
 name string
 email  string
 gender string
 age int
  }
  var people []Person
  err := json.Unmarshal(v, &people)
  if err != nil {
  }
  fmt.Println(people)
 }

http://play.golang.org/p/gHqiCLk-rV

will compile just fine, but will print out empty data.

Solution :

  1. Use JSON Linter to validate the JSON data. ( http://jsonlint.com/ )

  2. The variables names inside the Person struct starts with small cap, this means those variables are private type and cannot be displayed. Thus, this explains why the fmt.Println function prints out empty data. To fix the problem, change the variables names to start with big cap to make them public type. See the fixed code at http://play.golang.org/p/xLfz_aofCQ



Tags : golang fmt-println struct json

By Adam Ng

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