Charles Charles - 4 months ago 8
JSON Question

How Do I Parse a JSON file into a struct with Go

I'm trying to configure my Go program by creating a JSON file and parsing it into a struct:

var settings struct {
serverMode bool
sourceDir string
targetDir string
}

func main() {

// then config file settings

configFile, err := os.Open("config.json")
if err != nil {
printError("opening config file", err.Error())
}

jsonParser := json.NewDecoder(configFile)
if err = jsonParser.Decode(&settings); err != nil {
printError("parsing config file", err.Error())
}

fmt.Printf("%v %s %s", settings.serverMode, settings.sourceDir, settings.targetDir)
return
}


The config.json file:

{
"serverMode": true,
"sourceDir": ".",
"targetDir": "."
}


The Program compiles and runs without any errors, but the print statement outputs:

false


(false and two empty strings)

I've also tried with
json.Unmarshal(..)
but had the same result.

How do I parse the JSON in a way that fills the struct values?

Answer

You're not exporting your struct elements. They all begin with a lower case letter.

var settings struct {
    ServerMode bool `json:"serverMode"`
    SourceDir  string `json:"sourceDir"`
    TargetDir  string `json:"targetDir"`
}

Make the first letter of your stuct elements upper case to export them. The JSON encoder/decoder wont use struct elements which are not exported.