How to send JSON with QTcpSocket - c++

Question

I can send JSON object from client to server but can not get an item from JSON object on the server.
I've tried several examples that I found when I researched I can not solve the problem.
Code to send JSON:
QJsonObject levan{
{"id",1},
{"tipo","reforço"},
{"ca", 10},
{"cb",0},
{"cc",0},
{"cd",0},
{"ce",0},
{"cf",0},
{"cg",0},
{"ch",0},
};
QJsonArray jsarray {levan};
QJsonDocument jsDoc(jsarray);
QString jsString = QString::fromLatin1(jsDoc.toJson());
this->tcpSocket->write(jsString.toLatin1());
Code to receive JSON:
QString str = this->socket->readAll();
QJsonDocument jsonResponse = QJsonDocument::fromJson(str.toLatin1());
QJsonObject jsonObject = jsonResponse.object();
QJsonArray jsonArray = jsonObject["levantamento"].toArray();
qDebug()<< jsonResponse.object().value("levan");
if (jsonResponse.array().empty()) {
qDebug() << "empty";
}
I can present JSON as text, but I cannot get the items from the JSON.

Answer 1

You're creating a single QJsonObject and then creating a QJsonArray using that object. So, the final output is one JSON object with a nested array with only one object. I'm not sure if you intend to have only one object in array or an array of all those objects.
And, the JSON created in request is not what you're trying to read in response. There's no key levantamento or levan in your request so you cannot find anything against those in response. You need to work on population of objects in request JSON. The below example uses some of your test data for request population and extraction in response. Hope that helps!
Example:
#include <QDebug>
#include <QString>
#include <QJsonDocument>
#include <QJsonObject>
#include <QJsonArray>
int main()
{
// Request: Create JSON objects and array of objects
const auto jArrKey = "levan";
const auto jTstKey = "test";
const auto jRqObj1 = QJsonObject{ { "id", 1 } };
const auto jRqObj2 = QJsonObject{ { "cb", 0 } };
const auto jRqObj3 = QJsonObject{ { "cc", 0 } };
const auto jReqArr = QJsonArray{ jRqObj1, jRqObj2, jRqObj3 };
const auto jTstObj = QJsonObject{ { "Hello", "World" } };
const auto jReqObj = QJsonObject{ { jArrKey, jReqArr }, { jTstKey, jTstObj } };
const auto jReqDoc = QJsonDocument{ jReqObj };
const auto jReqStr = QString::fromLatin1( jReqDoc.toJson() );
qDebug() << "Request:\n" << qPrintable( jReqStr );
// Response: Read JSON document and inspect its elements
const auto jRspDoc = QJsonDocument::fromJson( jReqStr.toLatin1() );
const auto jRspObj = jRspDoc.object();
const auto jRspArr = jRspObj[ jArrKey ].toArray();
const auto jRspTst = jRspObj[ jTstKey ].toObject();
qDebug() << "Response:" << jRspArr;
qDebug() << "Test Obj:" << jRspTst;
qDebug() << ">> Hello:" << jRspTst.value( "Hello" ).toString();
return 0;
}
Output:
Request:
{
"levan": [
{
"id": 1
},
{
"cb": 0
},
{
"cc": 0
}
],
"test": {
"Hello": "World"
}
}
Response: QJsonArray([{"id":1},{"cb":0},{"cc":0}])
Test Obj: QJsonObject({"Hello":"World"})
>> Hello: "World"

Answer 2

You put an array as the document root, so retrieve it first:
QJsonDocument jsonResponse = QJsonDocument::fromJson(str.toLatin1());
QJsonArray jsonArray = jsonResponse.array();
Check if it's empty, if not get the first item (the levan object):
if(!jsonArray.isEmpty())
{
QJsonObject jsonObject = jsonArray.first().toObject();
You can now read the object keys, e.g.:
qDebug()<< jsonObject.value("tipo");
will print:
QJsonValue(string, "reforço")
Notice that levan is not a key, but a variable name. So this line:
jsonResponse.object().value("levan");
will never work.
If the issue persists, here's a couple of hints to debug your code.
First, check for parsing errors, this way:
QJsonParseError parseError;
QJsonDocument jsonResponse = QJsonDocument::fromJson(str.toLatin1(), &parseError);
if(parseError.error != QJsonParseError::NoError)
{
qDebug() << "Parse error: " << parseError.errorString();
}
If one occurs, just inspect the string (better: inspect it anyway), to see what came in:
qDebug() << str.toLatin1().data();
The expected output is:
[
{
"ca": 10,
"cb": 0,
"cc": 0,
"cd": 0,
"ce": 0,
"cf": 0,
"cg": 0,
"ch": 0,
"id": 1,
"tipo": "reforço"
}
]