I need to save values below pre-set levels, using QJsonDocument.
I have the following example of code:
(...)
gameLevels= {3.67, 7.43, 9.76};
while(gameLevels[i] <= x)
{
for(...)
{
//do something and calculate auxPoints.
}
QString sGL = QString::number(gameLevels[i]);
QString below = "below";
QString points = "pts";
instantPowerPoints.insert(below + sGL+ points , auxPoints);
i++;
(...)
}
emit saveData(QJsonDocument(instantPowerPoints));'
It should save something like:
"below3.67pts":2
"below7.43pts":6
"below9.76pts":10
But instead is saving:
"below3":Object
"67pts":2
"below7":Object
"43pts":6
"below9":Object
"76pts":10
I get the problem is how I save the array of doubles gameLevels. But I really need to have the number with the dot save as a string. Is there another way to save the string like this without automatically creating the object?
I am using C++ in QTCreator.
This should to the work
instantPowerPoints.insert(QString("%1 %2 %3").arg(below).arg(sGL).arg(points), auxPoints);
Related
I am new to Qt UI designer. We got a task to read a txt file, get a string out of it, and print it to a label via QDate.
So what I need, is to read a string, format it to QDate, and then format it to QString.
I tried doing it without an instance of QDate, but it did not work. The working code with an instance looks like:
QDate QDateInstance;
for (int i = 0; i < (int)TravelAgency1.FlightsList.size()-1; i++){
if (SearchedBooking == TravelAgency1.FlightsList[i]->getId()){
ui->ID_Output->setText(QString::number(TravelAgency1.FlightsList[i]->getId()));
QDateInstance = QDateInstance.fromString(QString::fromStdString(TravelAgency1.FlightsList[i]->getFromDate()),"yyyyMMdd");
ui->StartD_Output->setText(QDateInstance.toString());
QDateInstance = QDateInstance.fromString(QString::fromStdString(TravelAgency1.FlightsList[i]->getToDate()), "yyyyMMdd");
ui->EndD_Output->setText(QDateInstance.toString());
But I do not really like the declaration of an instance QDateInstance. I am guessing, there is a more elegant way of doing it.
Initially I was trying:
ui->StartD_Output->setText(QDate::toString(QDate::fromStdString(TravelAgency1.FlightsList[i]->getToDate()), "yyyyMMdd");
Any ideas?
I have a select query from which i want to store results in QT lists after query execution. Some of my code is:
QSqlQuery querySelect;
QStringList rfid;
QList<QDateTime> datetimeIN;
QList<QDateTime> datetimeOUT;
... Some other code + querySelect prepare.....
if(querySelect.exec())
{
while( querySelect.next() )
{
rfid.append(querySelect.value( 0 ).toString());
datetimeIN.append(querySelect.value( 1 ).toDateTime());
datetimeOUT.append(querySelect.value( 2 ).toDateTime());
}
}
else
{
qDebug() << querySelect.lastError();
}
I want to know is there another, more optimized faster approach to store the results in the lists, other than with the query.next while cycle because i think this is rather slow?
On the Qt side, the only optimization that I can think of is
querySelect.setForwardOnly(true)
By the way, I think you can change approach and create a single class and a list for it, rather then three separated lists.
struct Data
{
QString rfid;
QDateTime dtIn;
QDateTime dtOut;
};
Then store the results this way:
QList<Data> list;
while( querySelect.next() ) {
list.append( {querySelect.value(0).toString(),
querySelect.value(1).toDateTime(),
querySelect.value(2).toDateTime()} );
}
I need to serialize and parse multiple objects from my project, in order to save/load them when needed.
My objects will have exactly the same components : a QString name, an integer id, a QString description, and two integer x, y.
I'll need something like this :
{"name":"toto", "id":"42", "description":"tata", "x":"20", "y":"50"}
So I'll build my QJsonObject like this :
QJsonObject json;
json["id"] = object_to_serialize.get_id();
json["name"] = object_to_serialize.get_name();
json["description"] = object_to_serialize.get_description();
json["x"] = object_to_serialize.get_x();
json["y"] = object_to_serialize.get_y();
QJsonDocument filedoc(json);
file.write(filedoc.toJson);`
And in the file it will appear like this :
{"name":"toto", "id":"42", "description":"tata", "x":"20", "y":"50"}
{"name":"toto2", "id":"44", "description":"tata2", "x":"25", "y":"547"}
{"name":"toto3", "id":"46", "description":"tata3", "x":"21", "y":"580"}
My serialiser will take in parameter the object, the savefile name, and transform the object into a QJsonObject. It will need then to read the file to check if an object with the same id is here. If it is here, it will need to replace it, and if it is not, it will append it.
I'm a little lost between my serialization options and how to read it ;
Should I make a QJsonArray with multiple QJsonObject inside or QJsonObject with QJsonArrays ?
When I read it, I will need to check for the id ; but will a
foreach(object.value["id"] == 42)
//create the QJsonObject from the one with 42 and change it with the new data
will do to parse the object and not all of them ? Is there a better way ?
Thank you in advance for your answers.
You can have an array of json object, each of them having an ID so you can parse the relevant ones.
Although you could also parse all of them and add them in a map, as long as you don't have very heavy files it should be fine.
void parseJson(const QString &data)
{
QJsonDocument doc = QJsonDocument::fromJson(data.toUtf8());
if (doc.isNull())
{
war("invalid json document");
return;
}
QJsonArray jsonArray = doc.array();
foreach (const QJsonValue & value, jsonArray) {
QJsonObject obj = value.toObject();
if (obj.contains("id"))
{
if (obj["id"].toInt() == yourId) parseObject(obj);
}
}
}
void parseObject(const QJsonObject &obj)
{
if (obj.contains("valueA")) valueA = obj["valueA"].toDouble();
if (obj.contains("valueB")) valueB = obj["valueB"].toDouble();
}
This will work just fine if your file is not too big
Bigger Files
Now if you have very large file, it might be an issue to load it all in memory and parse it.
Since your structure is always the same and quite simple, JSON might not be the best choice, one more efficient method would be to do your own parser (or use probably some existing ones) that could read the file and process it as a stream.
Another method, would be to have one JSON entry per line preceded by an ID with a fixed number of digit. Load this in a QHash lookup and then only read id of interest from the file and only parse a small section.
// This code is not tested and is just to show the principle.
#define IDSIZE 5
QHash<int64, int64> m_lookup; // has to be global var
// For very large file, this might take some time and can be done on a separate thread.
// it needs to be done only once at startup (given the file is not modified externally)
void createLookup(const QString &fileName)
{
QFile inputFile(fileName);
if (inputFile.open(QIODevice::ReadOnly))
{
QTextStream in(&inputFile);
while (!in.atEnd())
{
int position = in.pos(); // store the position in the file
QString line = in.readLine();
int id = line.mid(0,IDSIZE).toInt(); // 5 digit id (like 00001, 00002, etc...
m_lookup[id] = position + IDSIZE;
}
inputFile.close();
}
}
QString getEntry(const QString &fileName, int64 id)
{
if (m_lookup.contains(id))
{
QFile inputFile(fileName);
if (inputFile.open(QIODevice::ReadOnly))
{
inputFile.seek(m_lookup[id]);
QString data = inputFile.readLine();
inputFile.close();
return data;
} else {
return QString(); // or handle error
}
} else {
return QString(); // or handle error
}
}
// use example
QString data = getEntry(id);
if (data.length() > 0)
{
QJsonDocument doc = QJsonDocument::fromJson(data.toUtf8());
if (!doc.isNull())
{
// assign your variables
}
}
and your data file looking like this:
00042{"name":"toto", "id":"42", "description":"tata", "x":"20", "y":"50"}
00044{"name":"toto2", "id":"44", "description":"tata2", "x":"25", "y":"547"}
00046{"name":"toto3", "id":"46", "description":"tata3", "x":"21", "y":"580"}
The advantage of this method, it will only read the entry of interest, and avoid having to load MB or GB of data in memory just to get a specific entry.
This could further be improved with a lookup table stored at the beginning of the file.
The data of my file.txt is as below:
Student_ID=0001
Student_Name=joseph
Student_GradeLevel=2
How do I get the value, let say I want to get the Student_ID using Qt.
Thanks.
Take a look at this function, it can be used to find any value you want in your input file, where all lines are in the format you've posted above (key=value). If the key is not found, it returns an empty QString() object.
QString findValueInFile(QString key, QString filename) {
QFile file(filename);
if(file.open(QIODevice::ReadOnly)) {
QTextStream txtStr(&file);
QStringList fileContent = txtStr.readAll().split('\n');
for(auto &&line : fileContent) {
if(line.contains(key)) return line.split(QChar('='))[1];
}
file.close();
}
return QString(); // not found
}
Now you call it somewhere, e.g.:
qDebug() << findValueInFile("Student_ID", "file.txt");
qDebug() << findValueInFile("Student_Name", "file.txt");
This function can be easily modified if you replace your = sign with other delimiter e.g. => or sth else. However for key=value format there is a special QSettings class (mentioned by sebastian) that can allow you to read those values even easier:
QSettings file("file.txt", QSettings::IniFormat);
qDebug() << file.value("Student_Name").toString(); // et voila!
You can probably also use QSettings, as they are able to read ini files.
There are some caveats though regarding backslashes which might be important to you (though they aren't for the example you posted): http://doc.qt.io/qt-4.8/qsettings.html#Format-enum
QSettings iniFile("myfile.txt", QSettings::IniFormat);
// now get the values by their key
auto studentId = iniFile.value("Student_ID").toString().toInt();
I'm more of a PyQt user, so: apologies if I got some C++ specifics wrong...
Apologies for asking something this trivial but I just can't seem to get it right so I guess I've completely misunderstood everything I thought I knew about memory management.
I have a function that parses a network reply for some data and it looks like this:
// Call from another function
QVariantMap *mappedResult = handleReply(reply);
...
// Function
QVariantMap *handleReply(QNetworkReply *reply) {
QVariantMap *result = new QVariantMap;
QVariant testvalue = new QVariant("testvalue");
result->insert("testkey", testvalue);
if (reply->error() > 0) {
qDebug() << "Error number = " + reply->errorString();
QVariant variant = QVariant.fromValue(reply->errorString());
result->insert("error", variant);
} else {
QJsonDocument jsonResponse = QJsonDocument::fromJson(jsonString.toUtf8());
QJsonObject jsonResponseObject = jsonResponse.object();
*result = jsonResponseObject.toVariantMap();
}
return result;
}
If there is no error, the result is parsed fine by the built in toVariantMap function. When there is an error however, I would like to create an entry in the result that is sent back from the function. As you can see in the function, I'm trying to create QVariants from Strings in two different ways.
The first approach gives an error like this:
C:\Qt\5.2.0\mingw48_32\include\QtCore\qvariant.h:466: error: 'QVariant::QVariant(void*)' is private inline QVariant(void *) Q_DECL_EQ_DELETE;
^
The second approach like this:
[PATH] error: expected primary-expression before '.' token QVariant variant = QVariant.fromValue(reply->errorString());
I've also tried setting the values like this:
result->insert("testkey", "testvalue");
result->insert("error", reply->errorString());
The last approach doesn't give compile errors but the result variable in the return statement cannot be inspected in the debugger and as soon as the return statement is executed the application crashes with memory problems indicating I'm not using "new" properly.
"Error accessing memory address 0x...".
If someone with at least a little knowledge could help me sort out how to perform this simple task, I would be very greatful. How can I return a QVariantMap from my function with custom strings as key/value pairs?
Cheers.
I would write your function in the following way (with fixes):
QVariantMap *handleReply(QNetworkReply *reply) {
QVariantMap *result = new QVariantMap;
QVariant testvalue("testvalue"); // <- fixed here
result->insert("testkey", testvalue);
if (reply->error() > 0) {
qDebug() << "Error number = " + reply->errorString();
QVariant variant(reply->errorString()); // <- fixed here
result->insert("error", variant);
} else {
QJsonDocument jsonResponse = QJsonDocument::fromJson(jsonString.toUtf8());
QJsonObject jsonResponseObject = jsonResponse.object();
*result = jsonResponseObject.toVariantMap();
}
return result;
}
However it is still unclear, why do you need to work with a pointer to the variant map instread of passing it by value?