qt-cpp

name	qt-cpp
description	Comprehensive guide for developing cross-platform desktop applications with Qt in C++, including Qt5/Qt6, CMake, signals/slots, widgets, QML, threading, and deployment.
metadata	{"author":"mte90","version":"1.0.0","tags":["qt","c++","gui","desktop","qt6","cmake","cross-platform","qml","threading"]}

Qt C++ Development

Complete reference for building cross-platform desktop applications with Qt framework in C++.

Overview

Qt is a powerful C++ framework for cross-platform application development. It provides rich GUI capabilities, networking, database access, and more.

Key Characteristics:

• Cross-platform (Windows, macOS, Linux, mobile)
• Rich widget library and QML for modern UIs
• Signal-slot mechanism for event handling
• Meta-Object System (MOC) for reflection
• Comprehensive documentation and examples

Qt Versions

Qt5 vs Qt6

Feature	Qt5	Qt6
C++ Standard	C++11	C++17 minimum
Graphics	OpenGL	Vulkan/Metal/DirectX
High-DPI	Manual	Enabled by default
QString	UTF-16	UTF-8 by default
Status	Maintenance	Active development

Use Qt 6 for: New projects, modern C++17/20 features, better graphics performance

Use Qt 5 for: Legacy codebases, Qt 5-only modules, platform constraints

Installation

Qt Online Installer (Recommended)

# Download from https://www.qt.io/download
# Install using the Qt Online Installer
# Select: Qt 6.x, Qt Creator, CMake, MinGW or MSVC

Package Managers

# macOS (Homebrew)
brew install qt@6
brew install cmake

# Ubuntu/Debian
sudo apt install qt6-base-dev qt6-tools-dev cmake

# Arch Linux
sudo pacman -S qt6-base cmake

Setting PATH

# Add to ~/.bashrc or ~/.zshrc
export PATH="/path/to/Qt/6.5.0/gcc_64/bin:$PATH"
export CMAKE_PREFIX_PATH="/path/to/Qt/6.5.0/gcc_64:$CMAKE_PREFIX_PATH"

CMake Build System

Basic CMakeLists.txt

cmake_minimum_required(VERSION 3.16)
project(MyQtApp VERSION 1.0.0 LANGUAGES CXX)

set(CMAKE_CXX_STANDARD 17)
set(CMAKE_CXX_STANDARD_REQUIRED ON)

set(CMAKE_AUTOMOC ON)
set(CMAKE_AUTORCC ON)
set(CMAKE_AUTOUIC ON)

find_package(Qt6 REQUIRED COMPONENTS Core Gui Widgets)

set(PROJECT_SOURCES
    main.cpp
    mainwindow.cpp
)

set(PROJECT_HEADERS
    mainwindow.h
)

set(PROJECT_FORMS
    mainwindow.ui
)

add_executable(MyQtApp
    ${PROJECT_SOURCES}
    ${PROJECT_HEADERS}
    ${PROJECT_FORMS}
)

target_link_libraries(MyQtApp
    Qt6::Core
    Qt6::Gui
    Qt6::Widgets
)

Advanced CMake Configuration

cmake_minimum_required(VERSION 3.20)
project(MyQtApp VERSION 1.0.0 LANGUAGES CXX)

set(CMAKE_CXX_STANDARD 17)
set(CMAKE_CXX_STANDARD_REQUIRED ON)

# Qt configuration
set(CMAKE_AUTOMOC ON)
set(CMAKE_AUTORCC ON)
set(CMAKE_AUTOUIC ON)
set(CMAKE_AUTORCC_OPTIONS "-binary")

# Find Qt6 packages
find_package(Qt6 REQUIRED COMPONENTS
    Core
    Gui
    Widgets
    Network
    Sql
    Xml
    Concurrent
)

# Find optional components
find_package(Qt6 QUIET COMPONENTS
    Quick
    QuickControls2
    Qml
    WebEngineWidgets
)

# Source files
set(PROJECT_SOURCES
    src/main.cpp
    src/mainwindow.cpp
    src/settingsdialog.cpp
)

set(PROJECT_HEADERS
    src/mainwindow.h
    src/settingsdialog.h
)

set(PROJECT_FORMS
    ui/mainwindow.ui
    ui/settingsdialog.ui
)

set(PROJECT_QML
    qml/Main.qml
)

set(PROJECT_RESOURCES
    resources/resources.qrc
)

# Create executable
add_executable(MyQtApp
    ${PROJECT_SOURCES}
    ${PROJECT_HEADERS}
    ${PROJECT_FORMS}
    ${PROJECT_QML}
    ${PROJECT_RESOURCES}
)

# Link libraries
target_link_libraries(MyQtApp PRIVATE
    Qt6::Core
    Qt6::Gui
    Qt6::Widgets
    Qt6::Network
    Qt6::Sql
    Qt6::Xml
    Qt6::Concurrent
)

# Optional: Qt Quick
if(TARGET Qt6::Quick)
    target_link_libraries(MyQtApp PRIVATE Qt6::Quick Qt6::Qml)
endif()

# Installation rules
install(TARGETS MyQtApp
    BUNDLE DESTINATION .
    RUNTIME DESTINATION ${CMAKE_INSTALL_BINDIR}
)

Building

mkdir build && cd build
cmake ..
cmake --build .
./MyQtApp

Signals and Slots

Basic Signal-Slot Connection

// sender.h
#include <QObject>
#include <QTimer>

class Sender : public QObject {
    Q_OBJECT
public:
    explicit Sender(QObject *parent = nullptr) : QObject(parent) {
        m_timer = new QTimer(this);
        connect(m_timer, &QTimer::timeout, this, &Sender::timeout);
        m_timer->start(1000);
    }

signals:
    void timeout();
    void progress(int value);

private:
    QTimer *m_timer;
};

// receiver.h
#include <QObject>

class Receiver : public QObject {
    Q_OBJECT
public slots:
    void handleTimeout() {
        qDebug() << "Timeout received!";
    }

    void handleProgress(int value) {
        qDebug() << "Progress:" << value;
    }
};

// main.cpp
int main(int argc, char *argv[]) {
    QCoreApplication app(argc, argv);

    Sender sender;
    Receiver receiver;

    // Qt5 connection syntax
    QObject::connect(&sender, SIGNAL(timeout()),
                     &receiver, SLOT(handleTimeout()));

    // Qt6 modern connection syntax (recommended)
    QObject::connect(&sender, &Sender::timeout,
                     &receiver, &Receiver::handleTimeout);

    return app.exec();
}

Lambda Connections

class MainWindow : public QMainWindow {
    Q_OBJECT
public:
    MainWindow(QWidget *parent = nullptr) : QMainWindow(parent) {
        QPushButton *button = new QPushButton("Click me", this);

        // Lambda with capture
        connect(button, &QPushButton::clicked, this, [this]() {
            handleButtonClick();
        });

        // Lambda with parameters
        connect(button, &QPushButton::clicked, this, [=](bool checked) {
            qDebug() << "Button clicked:" << checked;
        });

        // Lambda with context object
        connect(button, &QPushButton::clicked,
                this, [this]() {
                    this->handleButtonClick();
                },
                Qt::QueuedConnection);
    }

private:
    void handleButtonClick() {
        qDebug() << "Button clicked!";
    }
};

Connection Types

// Auto Connection (default)
connect(sender, &Sender::signal, receiver, &Receiver::slot);
// Uses DirectConnection if receiver and sender are in same thread
// Uses QueuedConnection otherwise

// Direct Connection (same thread only)
connect(sender, &Sender::signal, receiver, &Receiver::slot,
        Qt::DirectConnection);
// Slot executes immediately in sender's thread

// Queued Connection (different threads)
connect(sender, &Sender::signal, receiver, &Receiver::slot,
        Qt::QueuedConnection);
// Slot executes in receiver's thread event loop

// Unique Connection (prevents duplicates)
connect(sender, &Sender::signal, receiver, &Receiver::slot,
        Qt::UniqueConnection);

// Blocking Queued Connection (blocks sender until slot finishes)
connect(sender, &Sender::signal, receiver, &Receiver::slot,
        Qt::BlockingQueuedConnection);

Signal Forwarding

class Relay : public QObject {
    Q_OBJECT
public:
    explicit Relay(QObject *parent = nullptr) : QObject(parent) {}

    // Relay signals
    void relaySignal(int value) {
        emit forwarded(value);
    }

signals:
    void forwarded(int value);
};

// Usage
Source source;
Relay relay;
Destination dest;

connect(&source, &Source::data, &relay, &Relay::relaySignal);
connect(&relay, &Relay::forwarded, &dest, &Destination::handleData);

Threading

QThread

class WorkerThread : public QThread {
    Q_OBJECT
public:
    explicit WorkerThread(QObject *parent = nullptr) : QThread(parent) {}

protected:
    void run() override {
        // Long-running operation
        for (int i = 0; i < 100; ++i) {
            QThread::msleep(100);
            emit progress(i);
        }
    }

signals:
    void progress(int value);
};

// Usage
class MainWindow : public QMainWindow {
    Q_OBJECT
public:
    MainWindow(QWidget *parent = nullptr) : QMainWindow(parent) {
        QPushButton *startButton = new QPushButton("Start", this);
        QProgressBar *progressBar = new QProgressBar(this);

        m_worker = new WorkerThread(this);

        connect(startButton, &QPushButton::clicked, this, [this]() {
            m_worker->start();
        });

        connect(m_worker, &WorkerThread::progress, progressBar,
                &QProgressBar::setValue);

        connect(m_worker, &WorkerThread::finished, this, []() {
            qDebug() << "Worker finished";
        });
    }

private:
    WorkerThread *m_worker;
};

QThreadPool and QRunnable

class MyTask : public QRunnable {
public:
    explicit MyTask(int id) : m_id(id) {}

    void run() override {
        // Background task
        qDebug() << "Task" << m_id << "running in thread:"
                 << QThread::currentThread();
        QThread::sleep(2);
    }

private:
    int m_id;
};

// Usage
QThreadPool pool;
pool.setMaxThreadCount(4);

for (int i = 0; i < 10; ++i) {
    pool.start(new MyTask(i));
}

// Wait for all tasks
pool.waitForDone();

QtConcurrent

#include <QtConcurrent>
#include <QFuture>
#include <QFutureWatcher>

// Run function in background
int heavyCalculation(int n) {
    QThread::sleep(2);
    return n * n;
}

int main(int argc, char *argv[]) {
    QCoreApplication app(argc, argv);

    // Run in separate thread
    QFuture<int> future = QtConcurrent::run(heavyCalculation, 42);

    // Watch for completion
    QFutureWatcher<int> watcher;
    connect(&watcher, &QFutureWatcher<int>::finished, &app, [&future]() {
        qDebug() << "Result:" << future.result();
        app.quit();
    });

    watcher.setFuture(future);

    return app.exec();
}

// Map-Reduce pattern
QVector<int> data = {1, 2, 3, 4, 5};

// Map: apply function to all elements
QFuture<QVector<int>> mapped = QtConcurrent::mapped(data, [](int n) {
    return n * n;
});

// Filter: keep elements that match
QFuture<QVector<int>> filtered = QtConcurrent::filtered(data, [](int n) {
    return n > 2;
});

moveToThread

class Worker : public QObject {
    Q_OBJECT
public:
    explicit Worker(QObject *parent = nullptr) : QObject(parent) {}

public slots:
    void doWork() {
        qDebug() << "Worker running in thread:"
                 << QThread::currentThread();
        QThread::sleep(2);
        emit workFinished("Done");
    }

signals:
    void workFinished(const QString &result);
};

class MainWindow : public QMainWindow {
    Q_OBJECT
public:
    MainWindow(QWidget *parent = nullptr) : QMainWindow(parent) {
        QThread *thread = new QThread(this);
        m_worker = new Worker();

        // Move worker to thread
        m_worker->moveToThread(thread);

        // Start thread
        connect(thread, &QThread::started, m_worker, &Worker::doWork);
        connect(m_worker, &Worker::workFinished, this,
                [](const QString &result) {
            qDebug() << "Result:" << result;
        });
        connect(m_worker, &Worker::workFinished, thread, &QThread::quit);
        connect(thread, &QThread::finished, thread, &QThread::deleteLater);
        connect(thread, &QThread::finished, m_worker, &Worker::deleteLater);

        thread->start();
    }

private:
    Worker *m_worker;
};

QML Integration

Exposing C++ Objects to QML

// dataobject.h
#include <QObject>
#include <QString>

class DataObject : public QObject {
    Q_OBJECT
    Q_PROPERTY(QString name READ name WRITE setName NOTIFY nameChanged)
    Q_PROPERTY(int value READ value WRITE setValue NOTIFY valueChanged)

public:
    explicit DataObject(QObject *parent = nullptr)
        : QObject(parent), m_value(0) {}

    QString name() const { return m_name; }
    void setName(const QString &name) {
        if (m_name != name) {
            m_name = name;
            emit nameChanged();
        }
    }

    int value() const { return m_value; }
    void setValue(int value) {
        if (m_value != value) {
            m_value = value;
            emit valueChanged();
        }
    }

    Q_INVOKABLE void reset() {
        setName("");
        setValue(0);
    }

signals:
    void nameChanged();
    void valueChanged();

private:
    QString m_name;
    int m_value;
};

// main.cpp
#include <QGuiApplication>
#include <QQmlApplicationEngine>
#include <QQmlContext>

int main(int argc, char *argv[]) {
    QGuiApplication app(argc, argv);

    QQmlApplicationEngine engine;

    // Register type
    qmlRegisterType<DataObject>("MyApp", 1, 0, "DataObject");

    // Or expose instance
    DataObject *obj = new DataObject(&app);
    obj->setName("Test");
    engine.rootContext()->setContextProperty("dataObject", obj);

    engine.load(QUrl(QStringLiteral("qrc:/qml/main.qml")));

    return app.exec();
}

QML File

import QtQuick 2.15
import QtQuick.Controls 2.15
import MyApp 1.0

ApplicationWindow {
    width: 400
    height: 300
    visible: true
    title: "Qt Quick Example"

    Column {
        anchors.centerIn: parent
        spacing: 10

        TextField {
            id: nameField
            placeholderText: "Enter name"
            text: dataObject.name
            onTextChanged: dataObject.name = text
        }

        SpinBox {
            value: dataObject.value
            onValueChanged: dataObject.value = value
        }

        Button {
            text: "Reset"
            onClicked: dataObject.reset()
        }

        Text {
            text: dataObject.name + " - " + dataObject.value
        }
    }
}

Q_PROPERTY Attributes

class Person : public QObject {
    Q_OBJECT
    // READ: getter method
    // WRITE: setter method (optional)
    // NOTIFY: signal emitted when value changes
    // CONSTANT: value never changes
    // FINAL: property cannot be overridden
    Q_PROPERTY(QString name READ name WRITE setName NOTIFY nameChanged CONSTANT FINAL)
    Q_PROPERTY(int age READ age WRITE setAge NOTIFY ageChanged)

public:
    QString name() const { return m_name; }
    void setName(const QString &name) {
        if (m_name != name) {
            m_name = name;
            emit nameChanged();
        }
    }

    int age() const { return m_age; }
    void setAge(int age) {
        if (m_age != age) {
            m_age = age;
            emit ageChanged();
        }
    }

signals:
    void nameChanged();
    void ageChanged();

private:
    QString m_name;
    int m_age;
};

Q_INVOKABLE Methods

class Utility : public QObject {
    Q_OBJECT
public:
    explicit Utility(QObject *parent = nullptr) : QObject(parent) {}

    // Can be called from QML
    Q_INVOKABLE QString reverse(const QString &text) {
        QString reversed;
        for (int i = text.length() - 1; i >= 0; --i) {
            reversed += text[i];
        }
        return reversed;
    }

    Q_INVOKABLE void log(const QString &message) {
        qDebug() << "QML:" << message;
    }
};

Model/View Programming

QAbstractListModel

#include <QAbstractListModel>
#include <QVector>

class TodoModel : public QAbstractListModel {
    Q_OBJECT
public:
    enum Roles {
        TextRole = Qt::UserRole + 1,
        DoneRole
    };

    explicit TodoModel(QObject *parent = nullptr)
        : QAbstractListModel(parent) {}

    int rowCount(const QModelIndex &parent = QModelIndex()) const override {
        Q_UNUSED(parent);
        return m_todos.size();
    }

    QVariant data(const QModelIndex &index, int role) const override {
        if (!index.isValid() || index.row() >= m_todos.size())
            return QVariant();

        const Todo &todo = m_todos[index.row()];

        switch (role) {
        case TextRole:
            return todo.text;
        case DoneRole:
            return todo.done;
        default:
            return QVariant();
        }
    }

    QHash<int, QByteArray> roleNames() const override {
        QHash<int, QByteArray> roles;
        roles[TextRole] = "text";
        roles[DoneRole] = "done";
        return roles;
    }

    Q_INVOKABLE void add(const QString &text) {
        beginInsertRows(QModelIndex(), m_todos.size(), m_todos.size());
        m_todos.append({text, false});
        endInsertRows();
    }

    Q_INVOKABLE void remove(int index) {
        if (index < 0 || index >= m_todos.size())
            return;

        beginRemoveRows(QModelIndex(), index, index);
        m_todos.removeAt(index);
        endRemoveRows();
    }

    Q_INVOKABLE void toggle(int index) {
        if (index < 0 || index >= m_todos.size())
            return;

        m_todos[index].done = !m_todos[index].done;
        emit dataChanged(createIndex(index, 0),
                        createIndex(index, 0),
                        {DoneRole});
    }

private:
    struct Todo {
        QString text;
        bool done;
    };

    QVector<Todo> m_todos;
};

QML ListView with Model

import QtQuick 2.15
import QtQuick.Controls 2.15

ListView {
    width: 400
    height: 500
    model: todoModel
    delegate: ItemDelegate {
        width: ListView.view.width
        height: 50

        CheckBox {
            anchors.left: parent.left
            anchors.verticalCenter: parent.verticalCenter
            checked: model.done
            onClicked: todoModel.toggle(index)
        }

        Text {
            anchors.left: checkbox.right
            anchors.right: parent.right
            anchors.verticalCenter: parent.verticalCenter
            text: model.text
            elide: Text.ElideRight
        }
    }

    Button {
        anchors.bottom: parent.bottom
        anchors.right: parent.right
        text: "Add"
        onClicked: todoModel.add("New todo")
    }
}

Qt 6 Specific Features

QString UTF-8 by Default

// Qt5: UTF-16
QString text = "Hello";  // Internally UTF-16
QByteArray bytes = text.toUtf8();  // Need explicit conversion

// Qt6: UTF-8 by default
QString text = "Hello";  // Internally UTF-8
QByteArray bytes = text.toLatin1();  // Need explicit conversion for Latin-1

New Graphics Stack

// Qt6 uses RHI (Rendering Hardware Interface)
// Supports Vulkan, Metal, Direct3D 11/12, OpenGL

// For Qt Quick 3D
import QtQuick3D 6.0

Model {
    id: cube
    source: "#Cube"
    scale: Qt.vector3d(2, 2, 2)
}

Node {
    Model {
        id: sceneModel
        source: "#Rectangle"
        scale: Qt.vector3d(10, 10, 1)
        materials: PrincipledMaterial {
            baseColor: "green"
        }
    }
}

Properties

// Qt6 properties (similar to Q_PROPERTY but simpler)
class Counter : public QObject {
    Q_OBJECT
    Q_PROPERTY(int value READ value WRITE setValue NOTIFY valueChanged FINAL)

    QML_ELEMENT  // Register for QML

public:
    int value() const { return m_value; }
    void setValue(int value) {
        if (m_value != value) {
            m_value = value;
            emit valueChanged();
        }
    }

    // Property binding (Qt6 feature)
    Q_PROPERTY(int doubled READ doubled NOTIFY valueChanged FINAL)
    int doubled() const { return m_value * 2; }

signals:
    void valueChanged();

private:
    int m_value = 0;
};

Deployment

Windows (windeployqt)

# Build release
mkdir build && cd build
cmake .. -DCMAKE_BUILD_TYPE=Release
cmake --build . --config Release

# Deploy
windeployqt.exe --release MyQtApp.exe

# With plugins
windeployqt.exe --release --no-translations MyQtApp.exe

# With OpenSSL (if using QtNetwork with SSL)
windeployqt.exe --release --no-translations MyQtApp.exe
xcopy /E /I /Y C:\OpenSSL\*.dll deploy

macOS (macdeployqt)

# Build release
mkdir build && cd build
cmake .. -DCMAKE_BUILD_TYPE=Release
cmake --build . --config Release

# Deploy
macdeployqt MyQtApp.app -dmg

# With frameworks
macdeployqt MyQtApp.app -verbose=3

# Code sign (requires developer certificate)
codesign --deep --force --verify --verbose \
  MyQtApp.app

# Create DMG
hdiutil create -volname "MyQtApp" -srcfolder MyQtApp.app \
  -ov -format UDZO MyQtApp.dmg

Linux (linuxdeployqt)

# Install linuxdeployqt
wget https://github.com/linuxdeploy/linuxdeployqt/releases/download/continuous/linuxdeployqt-continuous-x86_64.AppImage
chmod +x linuxdeployqt-continuous-x86_64.AppImage

# Build release
mkdir build && cd build
cmake .. -DCMAKE_BUILD_TYPE=Release
cmake --build . --config Release

# Deploy
./linuxdeployqt-continuous-x86_64.AppImage MyQtApp

# Create AppImage
./linuxdeployqt-continuous-x86_64.AppImage \
  --appdir AppDir \
  --output appimage

CMake Installation Rules

# Platform-specific installation
if(WIN32)
    install(TARGETS MyQtApp
        RUNTIME DESTINATION .
    )

    # Deploy with windeployqt
    install(CODE
        "${CMAKE_COMMAND}" -E env "PATH=$ENV{PATH}"
        "${CMAKE_PREFIX_PATH}/bin/windeployqt.exe"
        --dir "${CMAKE_INSTALL_PREFIX}"
        --no-translations
        MyQtApp.exe
    )
elseif(APPLE)
    install(TARGETS MyQtApp
        BUNDLE DESTINATION .
    )

    # Deploy with macdeployqt
    install(CODE
        execute_process(COMMAND ${CMAKE_PREFIX_PATH}/bin/macdeployqt
            "${CMAKE_INSTALL_PREFIX}/MyQtApp.app"
            -dmg)
    )
else()
    install(TARGETS MyQtApp
        RUNTIME DESTINATION bin
    )

    # Desktop file
    install(FILES MyQtApp.desktop
        DESTINATION share/applications)

    # Icons
    install(FILES icons/myqtapp.png
        DESTINATION share/icons/hicolor/256x256/apps)
endif()

Common Issues and Solutions

Memory Leaks

Problem: QObject children not deleted correctly

// ❌ BAD: Manual deletion can cause issues
delete myWidget;  // May crash if parent still exists

// ✅ GOOD: Use deleteLater() or parent-child system
myWidget->deleteLater();
// Or
myWidget->setParent(nullptr);
delete myWidget;

Thread Safety

Problem: GUI updates from wrong thread

// ❌ BAD: Updating UI from worker thread
class Worker : public QObject {
    void run() {
        label->setText("Done");  // CRASH!
    }
};

// ✅ GOOD: Use signals to update UI
class Worker : public QObject {
    void run() {
        emit updateText("Done");  // Safe
    }

signals:
    void updateText(const QString &text);
};

connect(worker, &Worker::updateText,
        label, &QLabel::setText,
        Qt::QueuedConnection);

Signal-Slot Connection Issues

Problem: Signals not connected

// ❌ BAD: Using old syntax in Qt6
connect(sender, SIGNAL(valueChanged(int)),
        receiver, SLOT(handleValue(int)));

// ✅ GOOD: Use modern syntax
connect(sender, &Sender::valueChanged,
        receiver, &Receiver::handleValue);

// ✅ GOOD: Runtime check
if (!connect(sender, &Sender::valueChanged,
              receiver, &Receiver::handleValue)) {
    qWarning() << "Failed to connect signal";
}

QML Binding Issues

Problem: Properties not updating in QML

// ❌ BAD: Forgetting NOTIFY
class Counter : public QObject {
    Q_PROPERTY(int value READ value WRITE setValue)  // Missing NOTIFY
};

// ✅ GOOD: Always include NOTIFY for writable properties
class Counter : public QObject {
    Q_PROPERTY(int value READ value WRITE setValue NOTIFY valueChanged)
    void setValue(int value) {
        if (m_value != value) {
            m_value = value;
            emit valueChanged();  // Must emit!
        }
    }
signals:
    void valueChanged();
};

Build Errors

Problem: MOC not running

# ❌ BAD: Missing AUTOMOC
add_executable(MyQtApp main.cpp mainwindow.cpp)
target_link_libraries(MyQtApp Qt6::Widgets)

# ✅ GOOD: Enable AUTOMOC
set(CMAKE_AUTOMOC ON)
add_executable(MyQtApp main.cpp mainwindow.cpp)
target_link_libraries(MyQtApp Qt6::Widgets)

Deployment Issues

Problem: Missing plugins on target system

# Windows: Missing DLLs
windeployqt.exe MyQtApp.exe --verbose

# macOS: Missing frameworks
macdeployqt MyQtApp.app --verbose=3

# Linux: Missing libraries
ldd ./MyQtApp  # Check dependencies

Best Practices

1. Always use Qt6 for new projects
2. Prefer modern signal-slot syntax (&Sender::signal)
3. Use deleteLater() instead of delete for QObjects
4. Enable AUTOMOC, AUTOUIC, AUTORCC in CMake
5. Use Q_PROPERTY for properties exposed to QML
6. Avoid blocking operations in main thread
7. Use moveToThread() for worker objects
8. Test on all target platforms early
9. Use Qt Creator's visual editors for UI design
10. Leverage Qt's extensive documentation and examples

Resources

• Official Documentation: https://doc.qt.io/qt-6/
• Qt Wiki: https://wiki.qt.io/
• Qt Forum: https://forum.qt.io/
• Examples: https://doc.qt.io/qt-6/examples-and-tutorials.html
• Qt Creator: https://www.qt.io/product/development-tools
• Qt Project Hosting: https://codereview.qt-project.org/

Quick Reference

Common Headers

#include <QApplication>      // GUI application
#include <QMainWindow>      // Main window
#include <QWidget>          // Basic widget
#include <QPushButton>      // Button
#include <QLabel>           // Text label
#include <QLineEdit>        // Text input
#include <QVBoxLayout>      // Layout
#include <QTimer>           // Timer
#include <QThread>          // Threading
#include <QNetworkAccessManager>  // Network
#include <QSqlDatabase>     // Database

Common CMake Components

find_package(Qt6 REQUIRED COMPONENTS
    Core        # Core non-GUI functionality
    Gui         # Window system, events
    Widgets     # UI widgets
    Network     # Network programming
    Sql         # SQL database
    Xml         # XML/SAX/DOM parsers
    Concurrent  # Threading utilities
)

Common Qt6 Modules

• Qt6::Core - Core functionality
• Qt6::Gui - Windowing, events, 2D graphics
• Qt6::Widgets - UI widgets
• Qt6::Quick - QML framework
• Qt6::Network - Network APIs
• Qt6::Sql - SQL database
• Qt6::Xml - XML processing
• Qt6::Test - Unit testing framework
• Qt6::Concurrent - Threading utilities