JSON parsing with QtJson...

filipdns

Hello,

I'm trying to parse value from JSON file:

[ { "geography": { "latitude": 51.1392, "longitude": 11.1481, "altitude": 11280.5, "direction": 68.9 }, "speed": { "horizontal": 805.37, "isGround": 0, "vertical": -3.90144 }, "departure": { "iataCode": "BVA", "icaoCode": "LFOB" }, "arrival": { "iataCode": "CIA", "icaoCode": "LIRA" }, "aircraft": { "regNumber": "EIGDT", "icaoCode": "B738", "icao24": "", "iataCode": "B738" }, "airline": { "iataCode": "FR", "icaoCode": "RYR" }, "flight": { "iataNumber": "FR92QB", "icaoNumber": "RYR92QB", "number": "92QB" }, "system": { "updated": "1543065538", "squawk": "1127" }, "status": "en-route" }, { "geography": { "latitude": 43.4357, "longitude": 18.9397, "altitude": 11280.5, "direction": 136 }, "speed": { "horizontal": 914.949, "isGround": 0, "vertical": -5.20192 }, "departure": { "iataCode": "BVA", "icaoCode": "LFOB" }, "arrival": { "iataCode": "SKG", "icaoCode": "LGTS" }, "aircraft": { "regNumber": "EIEKI", "icaoCode": "B738", "icao24": "4CA808", "iataCode": "B738" }, "airline": { "iataCode": "FR", "icaoCode": "RYR" }, "flight": { "iataNumber": "FR3094", "icaoNumber": "RYR3094", "number": "3094" }, "system": { "updated": "1543065479", "squawk": "664" }, "status": "en-route" } ]

with


   QByteArray data= reply->readAll();
   QString datastring = QString::fromStdString(data.toStdString());
    //qDebug()<<data;

    bool ok;
    // datastring is a QString containing the JSON data
    QtJson::JsonObject result = QtJson::parse(datastring, ok).toMap();

    if(!ok) {
      qFatal("An error occurred during parsing");
    }

    qDebug() << "latitude:" << result["latitude"].toString();

but the result say only:

latitude: ""

What I did wrong?

[Moved to General and Desktop ~kshegunov]

kshegunov

It seems I've moved this in error.
What is QtJson and where it comes from, and why are you using that instead of Qt's own facilities ...?

filipdns

@kshegunov Hello,

I use it because I found only readable example on this.

May be I can use something else but I don't know how

kshegunov

My point was Qt already has support for JSON, so I have no idea why you pulled an additional dependency is all.

filipdns

@kshegunov thanks a lot, I will check on it

filipdns

@kshegunov Hello, I try following support for JSON but doesn't work...

json file:
{ "aircraft":[
{
"geography": {
"latitude": 42.6581,
"longitude": 5.51009,
"altitude": 11585.4,
"direction": 16
},
"speed": {
"horizontal": 861.641,
"isGround": 0,
"vertical": 0
},
"departure": {
"iataCode": "DJE",
"icaoCode": "DTTJ"
},
"arrival": {
"iataCode": "ORY",
"icaoCode": "LFPO"
},
"aircraft": {
"regNumber": "FGZHS",
"icaoCode": "B738",
"icao24": "3964F2",
"iataCode": "B738"
},
"airline": {
"iataCode": "TO",
"icaoCode": "TVF"
},
"flight": {
"iataNumber": "TO3875",
"icaoNumber": "TVF3875",
"number": "3875"
},
"system": {
"updated": "1543087861",
"squawk": "7376"
},
"status": "started"
}
]}

function getFlight(registration)
{
    var res
    var url = 'http://aviation-edge.com/v2/public/flights?key=2a8619-db5a5c&regNum=FGZHS'
    var doc= new XMLHttpRequest()
    doc.onreadystatechange = function(){
        if(doc.readyState == XMLHttpRequest.DONE){
            res=doc.responseText
            console.log(res)
            var obj =JSON.parse(res)
           console.log(obj.geography)
        }
    }
    doc.open('GET', url, true)
    doc.send()
}

with console.log(res) I display the correct content from file
but with console.log(obj.geography) I receive undefined on console...

Christian Ehrlicher

Because it's inside an array:

[ ... ]

filipdns

@Christian-Ehrlicher thanks, then, what I have to do to extract the data what I need?...

Christian Ehrlicher

@filipdns said in JSON parsing with QtJson...:

what I have to do to extract the data what I need?...

Extract the array I would guess... http://doc.qt.io/qt-5/qjsonarray.html

filipdns

@Christian-Ehrlicher I try to work with it like array:

var obj =JSON.parse(res)
console.log(obj.aircraft[0].geography)

but the return message is [object Object]...

Christian Ehrlicher

Sorry but I don't understand python that much to help you.

mrjj

Hi

{
  "aircraft":[
    {
      "geography":{
        "latitude":42.6581,
        "longitude":5.51009,
        "altitude":11585.4,
        "direction":16
      },
      "speed":{
        "horizontal":861.641,
        "isGround":0,
        "vertical":0
      },
      "departure":{
        "iataCode":"DJE",
        "icaoCode":"DTTJ"
      },
      "arrival":{
        "iataCode":"ORY",
        "icaoCode":"LFPO"
      },
      "aircraft":{
        "regNumber":"FGZHS",
        "icaoCode":"B738",
        "icao24":"3964F2",
        "iataCode":"B738"
      },
      "airline":{
        "iataCode":"TO",
        "icaoCode":"TVF"
      },
      "flight":{
        "iataNumber":"TO3875",
        "icaoNumber":"TVF3875",
        "number":"3875"
      },
      "system":{
        "updated":"1543087861",
        "squawk":"7376"
      },
      "status":"started"
    }
  ]
}

Would obj.aircraft[0].geography
not be an object ? with keys latitude,longitude etc ?

kshegunov

Firstly, what is this language? JS?
Secondly, what is JSON in your code and where does it come from?

filipdns

@kshegunov Hello,

Yes, it's JS language to get the network response.

the JSON response is come from http://aviation-edge.com

with request like http://aviation-edge.com/v2/public/flights?key=2a8619-db5a5c&regNum=ECMJT

kshegunov

I am now completely confused. How and why is this JS executed and what relation does it bear to Qt? Is this a QML function?

filipdns

@kshegunov Hi, it has no link with qt, it's just in case some one can help me to parse JSON with keys.

But did what I need parsing in JS but it's not very beautiful code like it is example:

                res=doc.responseText//JS.data(doc.responseText)
                //console.log(res)
                //var obj =JSON.parse(res)
                var error="{\"error\": \"No Record Found or Flight not currently detected by receivers. \" }"
                if(res!==error)
                {
                    var res1=res.replace("[","")
                    var res2=res1.replace("{","")
                    var res3=res2.split("{")
                    var res4=res3[1]
                    var res5= res4.split(",")
                    var res6=res5[0]+res5[1]+res5[2]+res5[3]
                    var res7=res6
                    var res8=res7.replace("\n","")
                    var res9=res8.replace("            ","")
                    var res10=res9.replace("\"","")
                    var res11=res10.split(":")
                    var res12=res11[0].replace("\"","") //text: latitude
                    var res13=res11[1].split("\n")
                    var res14=parseFloat(res13[0])      //valeur latitude
                    var res15=res13[1].replace("            \"","")
                    var res16=res15.replace("\"","")    //text longitude
                    var res17=parseFloat(res11[2].split("\n")[0])// valeur longitude
                    var res18=parseInt(parseFloat(res11[3].split("\n")[0])*3.28084/100) // valeur altitude
                    var res19 = parseInt(res11[4].split("\n")[0]) // valeur cap

Taz742

@filipdns
It is not a valid json file. https://forum.qt.io/topic/64314/json-access-data-in-multidimensional-arrays/8

filipdns

@Taz742 thank you, I will stay with my poor code then lol

aha_1980

@filipdns

Did you read the post @Taz742 linked?

Your top-level structure is a JSON array, so you must convert the document to a QJsonArray, not a QJsonObject.

Using a QJsonArray should work for you, too.

filipdns

@aha_1980 Hello, I start to read yes, I'm trying to understand how do that in js, I found documentation on QJsonArray only for c++ at the moment