sudo apt install qt5-default qtcreator

find_package(Qt6 REQUIRED COMPONENTS Core Widgets Network Sql)
target_link_libraries(MyApp Qt6::Core Qt6::Widgets Qt6::Network)
 
# Required for MOC, UIC, RCC
set(CMAKE_AUTOMOC ON)
set(CMAKE_AUTOUIC ON)
set(CMAKE_AUTORCC ON)

#include <QObject>
#include <QDebug>
 
class Counter : public QObject {
    Q_OBJECT  // required macro for MOC
 
public:
    Counter(QObject* parent = nullptr) : QObject(parent), m_value(0) {}
 
    int value() const { return m_value; }
 
public slots:
    void setValue(int val) {
        if (val != m_value) {
            m_value = val;
            emit valueChanged(val);  // emit signal
        }
    }
 
signals:
    void valueChanged(int newValue);
 
private:
    int m_value;
};
 
// Connect signal to slot
Counter a, b;
QObject::connect(&a, &Counter::valueChanged,
                 &b, &Counter::setValue);
 
a.setValue(42);  // b.value() is now 42
qDebug() << b.value(); // 42

#include <QApplication>
#include <QLabel>
 
int main(int argc, char* argv[]) {
    QApplication app(argc, argv);
 
    QLabel label("Hello, Qt!");
    label.setWindowTitle("My App");
    label.resize(300, 100);
    label.show();
 
    return app.exec(); // event loop
}

#include <QWidget>
#include <QPushButton>
#include <QLineEdit>
#include <QLabel>
#include <QVBoxLayout>
 
class MyWindow : public QWidget {
    Q_OBJECT
public:
    MyWindow(QWidget* parent = nullptr) : QWidget(parent) {
        auto* layout = new QVBoxLayout(this);
 
        auto* label = new QLabel("Enter name:");
        auto* input = new QLineEdit();
        auto* btn   = new QPushButton("Greet");
        auto* result = new QLabel();
 
        layout->addWidget(label);
        layout->addWidget(input);
        layout->addWidget(btn);
        layout->addWidget(result);
 
        connect(btn, &QPushButton::clicked, [=]() {
            result->setText("Hello, " + input->text() + "!");
        });
    }
};

QVBoxLayout* vbox = new QVBoxLayout();  // vertical stack
QHBoxLayout* hbox = new QHBoxLayout();  // horizontal stack
QGridLayout* grid = new QGridLayout();  // grid
QFormLayout* form = new QFormLayout();  // label-field pairs
 
// Grid example
grid->addWidget(widget1, 0, 0);  // row 0, col 0
grid->addWidget(widget2, 0, 1);  // row 0, col 1
grid->addWidget(widget3, 1, 0, 1, 2); // row 1, col 0, span 1 row 2 cols

// main.qml
import QtQuick 2.15
import QtQuick.Controls 2.15
 
ApplicationWindow {
    visible: true
    width: 400
    height: 300
    title: "Qt Quick App"
 
    Column {
        anchors.centerIn: parent
        spacing: 10
 
        Text {
            text: "Hello, QML!"
            font.pixelSize: 24
        }
 
        Button {
            text: "Click Me"
            onClicked: console.log("Clicked!")
        }
    }
}

// Expose C++ class to QML
class Backend : public QObject {
    Q_OBJECT
    Q_PROPERTY(QString message READ message WRITE setMessage NOTIFY messageChanged)
public:
    QString message() const { return m_msg; }
    void setMessage(const QString& msg) {
        m_msg = msg;
        emit messageChanged();
    }
signals:
    void messageChanged();
private:
    QString m_msg = "Hello from C++";
};
 
// Register in main.cpp
qmlRegisterType<Backend>("com.myapp", 1, 0, "Backend");
 
// Use in QML
// Backend { id: backend }
// Text { text: backend.message }

#include <QNetworkAccessManager>
#include <QNetworkRequest>
#include <QNetworkReply>
 
QNetworkAccessManager* manager = new QNetworkAccessManager(this);
 
connect(manager, &QNetworkAccessManager::finished,
        [](QNetworkReply* reply) {
            if (reply->error() == QNetworkReply::NoError) {
                QByteArray data = reply->readAll();
                qDebug() << data;
            }
            reply->deleteLater();
        });
 
manager->get(QNetworkRequest(QUrl("https://api.example.com/data")));

#include <QSqlDatabase>
#include <QSqlQuery>
#include <QSqlError>
 
QSqlDatabase db = QSqlDatabase::addDatabase("QSQLITE");
db.setDatabaseName("myapp.db");
 
if (!db.open()) {
    qDebug() << "DB error:" << db.lastError().text();
    return;
}
 
QSqlQuery query;
query.exec("CREATE TABLE IF NOT EXISTS users (id INTEGER PRIMARY KEY, name TEXT)");
 
query.prepare("INSERT INTO users (name) VALUES (:name)");
query.bindValue(":name", "Alice");
query.exec();
 
query.exec("SELECT id, name FROM users");
while (query.next()) {
    int id = query.value(0).toInt();
    QString name = query.value(1).toString();
    qDebug() << id << name;
}

#include <QThread>
#include <QRunnable>
#include <QThreadPool>
 
// Worker using QRunnable + thread pool
class Worker : public QRunnable {
public:
    void run() override {
        // heavy work here (runs in thread pool)
        qDebug() << "Running in thread:" << QThread::currentThreadId();
    }
};
 
QThreadPool::globalInstance()->start(new Worker());
 
// QtConcurrent for simple parallel tasks
#include <QtConcurrent>
QFuture<void> future = QtConcurrent::run([]() {
    // runs in thread pool
});
future.waitForFinished();