My structures are not marshalling into json [duplicate] - json

Question

This question already has answers here:
json.Marshal(struct) returns "{}"
(3 answers)
Closed 3 years ago.
I am using Go 1.0.3 on Mac OS X 10.8.2, and I am experimenting with the json package, trying to marshal a struct to json, but I keep getting an empty {} json object.
The err value is nil, so nothing is wrong according to the json.Marshal function, and the struct is correct. Why is this happening?
package main
import (
"encoding/json"
"fmt"
)
type Address struct {
street string
extended string
city string
state string
zip string
}
type Name struct {
first string
middle string
last string
}
type Person struct {
name Name
age int
address Address
phone string
}
func main() {
myname := Name{"Alfred", "H", "Eigenface"}
myaddr := Address{"42 Place Rd", "Unit 2i", "Placeton", "ST", "00921"}
me := Person{myname, 24, myaddr, "000 555-0001"}
b, err := json.Marshal(me)
if err != nil {
fmt.Println(err)
}
fmt.Println(string(b)) // err is nil, but b is empty, why?
fmt.Println("\n")
fmt.Println(me) // me is as expected, full of data
}

Answer 1

You have to make the fields that you want to marshal public.
Like this:
type Address struct {
Street string
Extended string
City string
State string
Zip string
}
err is nil because all the exported fields, in this case there are none, were marshalled correctly.
Working example: https://play.golang.org/p/9NH9Bog8_C6
Check out the docs http://godoc.org/encoding/json/#Marshal

Answer 2

Note that you can also manipulate what the name of the fields in the generated JSON are by doing the following:
type Name struct {
First string `json:"firstname"`
Middle string `json:"middlename"`
Last string `json:"lastname"`
}

Answer 3

JSON library cannot view the fields in a struct unless they are public. In your case,
type Person struct {
name Name
age int
address Address
phone string
}
the fields name, age, address and phone are not public (start with a small letter). In golang, variables/functions are public, when they start with a capital letter. So for this to work, your struct needs to look something like this:
type Person struct {
Name Name
Age int
Address Address
Phone string
}