encoding/json unmarshal missing a field

问题

The following code unmarshal's the "Id", but not the "Hostname". Why? I've been staring at it for long enough now that if it's a typo I know I'll never spot it. Help please. (http://play.golang.org/p/DIRa2MvvAV)

package main

import (
    "encoding/json"
    "fmt"
)

type jsonStatus struct {
    Hostname string `json:host`
    Id       string `json:id`
}

func main() {
    msg := []byte(`{"host":"Host","id":"Identifier"}`)

    status := new(jsonStatus)

    err := json.Unmarshal(msg, &status)
    if err != nil {
        fmt.Println("Unmarshall err", err)
    }
    fmt.Printf("Got status: %#v\n", status)
}

The output I get is

Got status: &main.jsonStatus{Hostname:"", Id:"Identifier"}

where I expect

Got status: &main.jsonStatus{Hostname:"Host", Id:"Identifier"}

回答1:

Your field tags are wrong. They need quotes around the alternate name.

type jsonStatus struct {
    //--------------------v----v
    Hostname string `json:"host"`
    Id       string `json:"id"`
}

Technically, you don't need a tag for the Id field at all. That's why that field was working.

DEMO: http://play.golang.org/p/tiop27jNJe

来源：https://stackoverflow.com/questions/16021487/encoding-json-unmarshal-missing-a-field

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json

serialization