Charles Charles - 1 year ago 68
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)

The config.json file:

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

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


(false and two empty strings)

I've also tried with
but had the same result.

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

Answer Source

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.

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