2015-02-09 13:56



I would like to create a JSON of a GatewayInfo where the type are defined like this:

type SpanInfo struct {
    imsi string
    network string
    network_status string
    signal_quality int
    slot int
    state string

type GatewayInfo []SpanInfo

The gateway information is created with:

var gatewayInfo = make(GatewayInfo, nb_spans)

To create the JSON, I use the json.Marshal function:

gatewayInfo := getGatewayInfo(spans)
log.Printf("Polling content: %s
", gatewayInfo)

jsonInfo, _ := json.Marshal(gatewayInfo)
log.Printf("jsonInfo: %s
", jsonInfo)

Unfortunately the result is not what I was expecting:

2015/02/09 13:48:26 Polling content: [{652020105829193 20801 Registered (Roaming) %!s(int=17) %!s(int=2) } {652020105829194 20801 Registered (Roaming) %!s(int=16) %!s(int=3) } {652020105829192 20801 Registered (Roaming) %!s(int=19) %!s(int=1) } {652020105829197 20801 Registered (Roaming) %!s(int=19) %!s(int=4) }]
2015/02/09 13:48:26 jsonInfo: [{},{},{},{}]

As we can see, the GatewayInfo instance has the SpanInfo, but in the JSON I have empty SpanInfo.

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  • duanchi6397 duanchi6397 6年前

    Your struct fields must be exported (field is exported if it begins with a capital letter) or they won't be encoded:

    Struct values encode as JSON objects. Each exported struct field becomes a member of the object

    To get the JSON representation as probably expected change the code to this:

    type SpanInfo struct {
        IMSI string `json:"imsi"`
        Network string `json:"network"`
        NetworkStatus string `json:"network_status"`
        SignalQuality int `json:"signal_quality"`
        Slot int `json:slot"`
        State string `json:"state"`
    type GatewayInfo []SpanInfo
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  • dsxxqndv41105 dsxxqndv41105 6年前

    The json package can only serialize exported fields of your struct. Change your struct to start all fields with an uppercase letter so they can be included in the output:

    type SpanInfo struct {
        Imsi string
        Network string
        Network_status string
        Signal_quality int
        Slot int
        State string

    Read the documentation of json.Marshal() for details and more information.

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