reading JSON file in Qt5

Hi,

I have been trying to figure out how to read a JSON file using Qt5 QJsonDocument with no success so far.
I can't find any examples online. If someone could give me a simple example I would appreciate it.

Here is my code::

Code:

---

QFile file;
file.setFileName("/tmp/settings.json");
file.open(QIODevice::ReadOnly | QIODevice::Text);
QJsonDocument settdoc;
settdoc.fromBinaryData(file.readAll());
qDebug() << settdoc.isNull();

---

settdoc.isNull() returns true, I can read the file into a stream without any issue and I validated the json as well.

Thank you

Laszlo

Does /tmp/settings.json exists? Is it well formed? Also try QJsonDocument::fromJson and see what error (QJsonParseError) you get.

EDIT: Forget the first questions....

EDIT 2:

Code:

---

QString str = "{"
                  "  \"Herausgeber\": \"Xema\","
                  "  \"Nummer\": \"1234-5678-9012-3456\","
                  "  \"Deckung\": 2e+6,"
                  "  \"Währung\": \"EURO\","
                  "  \"Inhaber\": {"
                  "    \"Name\": \"Mustermann\","
                  "    \"Vorname\": \"Max\","
                  "    \"männlich\": true,"
                  "    \"Hobbys\": [ \"Reiten\", \"Golfen\", \"Lesen\" ],"
                  "    \"Alter\": 42,"
                  "    \"Kinder\": [],"
                  "    \"Partner\": null"
                  "  }"
                  "}";
    QJsonDocument d = QJsonDocument::fromJson(str.toUtf8());
    qWarning() << d.isNull();

---

See if that works for you and then replace str.toUtf8() through your readAll().

Thank you for your fast reply and even more thank you for your example code!!
It works now! I somehow overlooked that I can use toUtf8() on a QString.
You example put me in the right track and now I can adjust basic window properties with my json file :D
Now just need to work on auto copy this file into the apps resources at runtime.

Here is my working code::

Code:

---

QString settings;
QFile file;
file.setFileName("/tmp/settings.json");
file.open(QIODevice::ReadOnly | QIODevice::Text);
settings = file.readAll();
file.close();
 
QJsonDocument sd = QJsonDocument::fromJson(settings.toUtf8());
qWarning() << sd.isNull(); // <- print false :)
QJsonObject sett2 = sd.object();
qWarning() << sett2.value(QString("title"));  // <- print my title

---

Thanks again, totally made my morning :)

Laszlo

You are aware that this requires two codec conversions, right?

Code:

---

settings = file.readAll()

---

converts from UTF-8 to UTF-16 and

Code:

---

settings.toUtf8()

---

converts from UTF-16 to UTF-8.

Since start and end encoding are the same (UTF-8) those two conversions are unneeded.

Why don't you just call fromJson() with the QByteArray returned by file.readAll()?

Also: the problem with your original code has nothing to do with the content at all, you are calling a static method and are then wondering why it didn't change an instance.

Static methods can't do that.
Hint: in Qt methods that are called fromABCD usually return something.

Cheers,
_

QString filename = QFileDialog::getOpenFileName();

QString val;
QFile file;
file.setFileName(filename);
file.open(QIODevice::ReadOnly | QIODevice::Text);
val = file.readAll();
file.close();
QJsonDocument d = QJsonDocument::fromJson(val.toUtf8());
QJsonObject Documento = d.object();

//{}= objet [] Array