Can't convert from QJsonValue to int.

HenkCoder

Hello I have a problem and I don't know how to solve it.
This is the JSON file:

 "toolBarColor": {
        "red": 156,
        "green": 244,
        "blue": 230
    },

and this my Qt code:

QFile file(QCoreApplication::applicationDirPath() + "/settings.json");
    QString input;
    file.open(QIODevice::ReadOnly | QIODevice::Text);
    input = file.readAll();
    QJsonDocument jsonDoc{QJsonDocument::fromJson(input.toUtf8())};
    file.close();
    QJsonObject jo{jsonDoc.object()};
    QJsonValue tempVal{jo.value("toolBarColor")};
    QJsonObject valueObj{tempVal.toObject()};
    QJsonValue redVal{valueObj.value("red")};
    QJsonValue greenVal{valueObj.value("green")};
    QJsonValue blueVal{valueObj.value("blue")};
    int red{redVal.toInt()};
    int green{greenVal.toInt()};
    int blue{blueVal.toInt()};

I don't know why, but this returns just the default value 0.
Can you please explain me how to solve this?

HenkCoder

@Christian-Ehrlicher I used that but the problem was that the file contained a JSON array first

JoeCFD

You may always need to do the following in your code:

if ( false == file.open(QIODevice::ReadOnly | QIODevice::Text)) {
    print out open failed.
    return.
}

input = file.readAll();
if ( input.isEmpty() ) {
    print out empty file message
    return;
}

if ( true == jsonDoc.isEmpty() ) {
    print out message
    return
}

HenkCoder

@JoeCFD It does open properly and I have added that place of code but it still does this thing

JonB

@HenkCoder said in Can't convert from QJsonValue to int.:

QJsonValue tempVal{jo.value("toolBarColor")};
QJsonObject valueObj{tempVal.toObject()};

Check what these two lines set. Easy to do in debugger. And while you're there look in QJsonValue redVal{valueObj.value("red")}; too!

P.S.
Actually don't bother. You have not put any error checking in (you always should), you haven't checked the very top-level

QJsonDocument jsonDoc{QJsonDocument::fromJson(input.toUtf8())};

You should find that is returning an empty document (and setting an error for you)? Assuming that is your file verbatim you have a trailing , (comma) right at the end. That is not legal: this is JSON, not C++! :)

Christian Ehrlicher

@HenkCoder said in Can't convert from QJsonValue to int.:

This is the JSON file:
"toolBarColor": {
"red": 156,
"green": 244,
"blue": 230
},

This is not a valid json file. Please use the second parameter from QJsonDocument::fromJson() to get noticed about parser errors.

JoeCFD

My following code works

QJsonObject jo{jsonDoc.object()};
JsonObject valueObj{jo["toolBarColor"]};
QJsonValue redVal{valueObj.value("red")};
QJsonValue greenVal{valueObj.value("green")};
QJsonValue blueVal{valueObj.value("blue")};

JoeCFD

@Christian-Ehrlicher You are right. It should be like this
{
"toolBarColor": {
"red": 156,
"green": 244,
"blue": 230
},
}

JonB

@JoeCFD said in Can't convert from QJsonValue to int.:

JsonObject valueObj{jo["toolBarColor"]};

That is treating it as a list of objects or as an object with attribute toolBarColor, I can't recall which. I still think you are "lucky" it parses, as (so far as I know) you are not supposed to end any JSON list of things with a trailing comma....

You have posted your last, and I still think you're not supposed to have the

    },
}

... :)

HenkCoder

@Christian-Ehrlicher Yes, I know, this is the full file:

{
    "font": {
        "family": "Calibri", 
        "pointSize": 11
    },

    "toolBarColor": {
        "red": 156,
        "green": 244,
        "blue": 230
    },
    
    "oldSplashscreen": false,
    "darkTheme": false
}

HenkCoder

This post is deleted!

HenkCoder

@JoeCFD I tried this code and it does not work either,
I have another line of code which sets the text of a textedit to red, green and blue variables and it still prints out "000".

JoeCFD

@JonB const QJsonValue QJsonDocument::operator[](const QString &key) const
https://doc.qt.io/qt-5/qjsondocument.html#operator-5b-5d

JonB

@HenkCoder
Then if that is the full file naturally you must access via jo["toolBarColor"].

Note that each time you use methods like QJsonValue::toInt(), and the other QJsonValue::to...() methods, you will get no error if the value is not of the type you think it is. Use the QJsonValue::is...() methods to check, QJsonValue::type() is your friend to tell you what you actually have.

JonB

@JoeCFD said in Can't convert from QJsonValue to int.:

@JonB const QJsonValue QJsonDocument::operator[](const QString &key) const
https://doc.qt.io/qt-5/qjsondocument.html#operator-5b-5d

I know this. Sorry, don't see the relevance.

HenkCoder

@JonB Hello, I tried and there is no isInt() method to verify it, I don't really know now

HenkCoder

@JonB to access that thing I did exactly what you said.

QJsonObject valueObj{jo["toolBarColor"].toObject()};
    QJsonValue redVal{valueObj.value("red")};
    QJsonValue greenVal{valueObj.value("green")};
    QJsonValue blueVal{valueObj.value("blue")};

this is the code but i don't know if it is right.

Christian Ehrlicher

Your code from the first post works fine for me. Make sure you're opening the correct json file. The conversion from/to QString is useless and wrong on non utf-8 systems though.

int main(int argc, char *argv[])
{
  QCoreApplication app(argc, argv);

  QByteArray content = R"(
{
    "font": {
        "family": "Calibri",
        "pointSize": 11
    },

    "toolBarColor": {
        "red": 156,
        "green": 244,
        "blue": 230
    },

    "oldSplashscreen": false,
    "darkTheme": false
}
)";
  QJsonDocument jsonDoc{QJsonDocument::fromJson(content)};
  QJsonObject jo{jsonDoc.object()};
  QJsonValue tempVal{jo.value("toolBarColor")};
  QJsonObject valueObj{tempVal.toObject()};
  QJsonValue redVal{valueObj.value("red")};
  QJsonValue greenVal{valueObj.value("green")};
  QJsonValue blueVal{valueObj.value("blue")};
  int red{redVal.toInt()};
  int green{greenVal.toInt()};
  int blue{blueVal.toInt()};
  qDebug() << red << green << blue;   // prints 156 244 230
  return 0;
}

JonB

@HenkCoder said in Can't convert from QJsonValue to int.:

@JonB Hello, I tried and there is no isInt() method to verify it, I don't really know now

So I said use QJsonValue::Type QJsonValue::type() const to check what type is in a QJsonValue before you assume you know what it is and use a non-erroring conversion method, especially when develeoping and it's not doing what you think....

Here you are assuming its type is Double QMetaType::Double or QMetaType::LongLong But if it;s Null or Undefined you are not where you think you are...

HenkCoder

Ooh now it works, I left a thing in the json file and forgot to save, I'm so dumb.
Thanks to all who tried to help me tho!

Christian Ehrlicher

@HenkCoder said in Can't convert from QJsonValue to int.:

I'm so dumb.

Please use the second parameter from QJsonDocument::fromJson() to get noticed about parser errors.

...