QJsonObject parameters order

[ODБOï]

hi,
i serialize an object with QJsonObject and write it to file

  static void saveRampe(QList<Tool*> rampe){
       
        QJsonArray rampeArr;
        QJsonObject jTool;

        for (auto &tool : rampe){
            jTool["nom"] = tool->nom();
            jTool["type"] = tool->typeToString();
            jTool["longueur"] = static_cast<double>(tool->longueur());
            jTool["diametre"] = static_cast<double>(tool->diametre());
            jTool["dureeVie"] = static_cast<double>(tool->dureeVie());
            jTool["tempsUsage"] = static_cast<double>(tool->tempsUtilisation());
            rampeArr.append(jTool);
        }

        QJsonDocument jrampe(rampeArr);
        QFile jsonFile("rampe.json");
        if(jsonFile.open(QFile::WriteOnly))
             jsonFile.write(jrampe.toJson());
}

but the output in the file does not respect the properties order

// current output
    {
        "diametre": 10, 
        "dureeVie": 600000, 
        "longueur": 100, 
        "nom": "T1", //<< this should be the first property
        "tempsUsage": 0,
        "type": "CYLINDRIQUE" 
    },

// suited output
    {   
        "nom": "T1", 
        "type": "CYLINDRIQUE",
        "longueur": 100,
        "diametre": 10,
        "dureeVie": 600000, 
        "tempsUsage": 0
    },

What is the reason ? is there a way to have the suited output witout using swap() ? edit : swap is not for that

[Christian Ehrlicher]

@LeLev said in QJsonObject parameters order:

What is the reason ?

There is no reason - json has no ordering of attributes in any way.

[JonB]

@LeLev
QJsonObject looks like it hold an unordered list/hash/map. The output you show it produces is alphabetical, as per https://doc.qt.io/qt-5/qjsonobject.html#keys

Returns a list of all keys in this object.

The list is sorted lexographically.

which is doubtless what it is using internally.

I suspect the only thing you could try if you care about the order would be https://doc.qt.io/qt-5/qjsonobject.html#constBegin etc., and see what order the iterator returns?

[KroMignon]

@LeLev said in QJsonObject parameters order:

What is the reason ?

as @Christian-Ehrlicher said there is no ordering of attributes for Json strings.
I think that QJsonObject, the values are stored in a QMap, and QMap are sorted by keys, so the attributes are alphabetic sorted ;)

That's it

[ODБOï]

@Christian-Ehrlicher , @JonB , @KroMignon
ok, thank you for the inputs

[JKSH]

This is not limited to QJsonObject.

See the official JSON specification (https://www.json.org/json-en.html ): "An object is an unordered set of name/value pairs."

Therefore, we should not expect or require our objects to be serialized in any specific order.

[Elmehdi]

@LeLev I'm now facing the same problem, did you find a way to make it work the way you wanted?

[ODБOï]

@Elmehdi no, i just let the file unordered