How to extract non {"key":"value"} JSON ?

[R-P-H]

Hi, I am receiving a JSON response using the following code:

QByteArray json = reply->readAll();
QJsonDocument data = QJsonDocument::fromJson(json);

This works perfectly for JSON such as:

{"mykey": "myvalue"}

which I can then access using data["mykey"].toString().

However, when I get a JSON response such as json = ""My value"", data is NULL.

How can I extract the JSON text correctly?

[Paul Colby]

HI @R-P-H ,

Besides converting the QByteArray to a QString, how would I extract the value if I added {} to the QByteArray ...

As long as the QByteArray contains a valid JSON value, you can either wrap it in [ and ] to make it a JSON array, or { "key": and } to make it a JSON object. If wrapping in an array, you would then fetch the first array item to get the original JSON value. Of if wrapping in an object, fetch the value corresponding to the key you used in the wrapper.

Here's a complete example:

    const QByteArray json{ "\"My Value\" "};
    qDebug().noquote() << "input               " << json;
    qDebug().noquote() << "parse-as-is         " << QJsonDocument::fromJson(json); // Will fail.

    const QJsonDocument arrayDoc = QJsonDocument::fromJson("[" + json + "]");
    qDebug().noquote() << "wrapped-in-array    " << arrayDoc;
    qDebug().noquote() << "unwrapped-array     " << arrayDoc.array().at(0);

    const QJsonDocument objectDoc = QJsonDocument::fromJson("{ \"value\": " + json + "}");
    qDebug().noquote() << "wrapped-in-object   " << objectDoc;
    qDebug().noquote() << "unwrapped-object    " << objectDoc.object().value(QStringLiteral("value"));

Which outputs:

input                "My Value" 
parse-as-is          QJsonDocument()
wrapped-in-array     QJsonDocument(["My Value"])
unwrapped-array      QJsonValue(string, My Value)
wrapped-in-object    QJsonDocument({"value":"My Value"})
unwrapped-object     QJsonValue(string, My Value)

Cheers.

[JonB]

@R-P-H
A complete response of ""My Value"", or for that matter "My Value", is not a JSON document. A JSON document must start with either [ (array) or { (object).

[R-P-H]

@JonB Besides converting the QByteArray to a QString, how would I extract the value if I added {} to the QByteArray so that it becomes {""My value""} and converted it to a QJsonDocument ?

[Christian Ehrlicher]

Since {"myvalue²} is no valid json - never.
See https://www.json.org/json-en.html

[Paul Colby]

HI @R-P-H ,

Besides converting the QByteArray to a QString, how would I extract the value if I added {} to the QByteArray ...

As long as the QByteArray contains a valid JSON value, you can either wrap it in [ and ] to make it a JSON array, or { "key": and } to make it a JSON object. If wrapping in an array, you would then fetch the first array item to get the original JSON value. Of if wrapping in an object, fetch the value corresponding to the key you used in the wrapper.

Here's a complete example:

    const QByteArray json{ "\"My Value\" "};
    qDebug().noquote() << "input               " << json;
    qDebug().noquote() << "parse-as-is         " << QJsonDocument::fromJson(json); // Will fail.

    const QJsonDocument arrayDoc = QJsonDocument::fromJson("[" + json + "]");
    qDebug().noquote() << "wrapped-in-array    " << arrayDoc;
    qDebug().noquote() << "unwrapped-array     " << arrayDoc.array().at(0);

    const QJsonDocument objectDoc = QJsonDocument::fromJson("{ \"value\": " + json + "}");
    qDebug().noquote() << "wrapped-in-object   " << objectDoc;
    qDebug().noquote() << "unwrapped-object    " << objectDoc.object().value(QStringLiteral("value"));

Which outputs:

input                "My Value" 
parse-as-is          QJsonDocument()
wrapped-in-array     QJsonDocument(["My Value"])
unwrapped-array      QJsonValue(string, My Value)
wrapped-in-object    QJsonDocument({"value":"My Value"})
unwrapped-object     QJsonValue(string, My Value)

Cheers.