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name qt-cpp
description Use when developing desktop applications with Qt in C++ - CMake setup, signals and slots, QThread and QtConcurrent, QML integration, model/view programming, Qt5 to Qt6 migration, or windeployqt/macdeployqt/linuxdeployqt deployment
metadata
author version tags
mte90
2.0.0
qt
c++
gui
desktop
qt6
cmake
cross-platform
qml
threading

Objective: Use this skill to reduce segfaults from raw pointers, signal/slot connection failures, memory leaks from parentless QObjects, and thread-assertion violations by enforcing ownership rules, connection patterns, and RAII discipline below.

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"

Deep Dives

Load these reference files for detailed guidance:

  • Signals and Slots — references/signals-slots.md — Connection syntax, lambda patterns, connection types, signal forwarding
  • Model/View Programming — references/model-view.md — QAbstractListModel, QML integration
  • Qt 6 Features — references/qt6-features.md — UTF-8 changes, graphics stack, properties
  • CMake Build System — references/cmake.md — CMake configuration, find_package, installation rules
  • Threading — references/threading.md — QThread, QThreadPool, QtConcurrent, moveToThread patterns
  • QML Integration — references/qml-integration.md — Exposing C++ to QML, Q_PROPERTY, Q_INVOKABLE
  • Deployment & Issues — references/deployment-issues.md — windeployqt, macdeployqt, linuxdeployqt, common problems
  • Quick Reference — references/quick-reference.md — Common headers, CMake components, module lookup

Signals and Slots

See references/signals-slots.md for connection syntax, lambda patterns, connection types, and signal forwarding.

Model/View Programming

See references/model-view.md for QAbstractListModel implementation and QML ListView integration.

Qt 6 Specific Features

See references/qt6-features.md for QString UTF-8 changes, graphics stack, and property syntax.

Best Practices

Do X because Y prevents Z patterns:

  1. Use parent pointers for all QObjects because orphaned objects leak memory when the event loop exits
  2. Prefer modern signal-slot syntax (&Sender::signal) because the old SIGNAL()/SLOT() macros bypass compile-time checking and cause runtime connection failures
  3. Call deleteLater() instead of delete because immediate deletion can crash if the object is still processing an event
  4. Enable AUTOMOC, AUTOUIC, AUTORCC in CMake because missing MOC generation causes "undefined reference to vtable" errors
  5. Use Q_PROPERTY for QML-exposed data because QML bindings require property notifications to update the UI
  6. Move long-running work to worker threads because blocking the main thread freezes the UI and triggers watchdog timeouts
  7. Use moveToThread() for worker objects because it ensures signals/slots queue correctly across thread boundaries
  8. Test deployment on each target platform early because windeployqt/macdeployqt issues often require platform-specific fixes
  9. Validate all user input at boundaries because Qt's string handling (especially UTF-8 in Qt6) can expose encoding bugs

Resources

Quick Reference

See references/quick-reference.md for common headers, CMake components, and module lookup.