CXX-Qt

Crate	Status
cxx-qt
cxx-qt-build
cxx-qt-lib
qt-build-utils

If you want to get in touch with us, feel free to join our Zulip Chat at: https://cxx-qt.zulipchat.com. There we openly discuss all things about CXX-Qt development.

CXX-Qt is a set of Rust crates for creating bidirectional Rust ⇄ C++ bindings with Qt. It can be used to integrate Rust into C++ applications using CMake or used to build Rust applications with Cargo. CXX-Qt provides tools for implementing QObject subclasses in Rust which can be used from C++, QML, and JavaScript. It consists of two parts:

• cxx-qt-lib, a library of Rust bindings to common QtCore and QtGui classes made with CXX

• cxx-qt & cxx-qt-build, a pair of Rust & C++ code generators which are a superset of CXX plus additional attributes to interface with Qt's signals & slots and property system. The cxx-qt crate implements a macro for Rust code generation. cxx-qt-build is used in Cargo build scripts to generate and compile the corresponding C++ code.

The CXX-Qt Book walks through a minimal example step-by-step and documents CXX-Qt's features for the latest release. The examples folder contains demonstrations of using threading, QQmlExtensionPlugin, and various other features.

CXX-Qt is tested on CI on Linux, Windows, macOS, and WebAssembly. It should work on other platforms that Qt and Rust both support, however, these are not tested regularly.

CXX-Qt is in early development and the API changes frequently. For the latest documentation between releases, install mdBook and run mdbook serve --open in the book folder. It will open your own browser. If you need to open it in another browser goto url http://localhost:3000.

Supported Qt Versions

We currently aim to support the Qt versions that have official support by the Qt company.

At the moment this means:

• Qt 5.15 LTS
• All versions of Qt 6

Versions below Qt 5.15 LTS are explicitly unsupported.

Comparison to other Rust Qt bindings

Project	Integrate into C++ codebase	Safe Rust	QML	QWidgets	Maintained1	Binding mechanism
CXX-Qt	✔	✔	✔	limited2	✔	cxx plus additional code generation to implement QObject subclasses in Rust and bind them to C++
qmetaobject	✗	✔	✔	✗	✔	cpp macro to write C++ inline in Rust, plus Rust macros to create QObject subclasses from Rust structs
Rust Qt Binding Generator	✔	✔	✔	limited2	✗	generates Rust traits and C++ bindings from JSON description of QObject subclass
rust-qt	✗	✗	✔	✔	✗	ritual to generate unsafe Rust bindings from C++ headers
qml-rust	✗	✔	✔	✗	✗	DOtherSide C wrapper for QML C++ classes
qmlrs	✗	✔	✔	✗	✗	own C++ library to bind QQmlApplicationEngine
qmlrsng	✗	✔	✔	✗	✗	libqmlbind with bindgen
rust-qml	✗	✔	✔	✗	✗	libqmlbind

¹: maintained: supports Qt6 and repository has had nontrivial commits within last year as of August 2022

²: CXX-Qt and Rust Qt Binding Generator can be used to implement custom QObjects subclasses in Rust. C++ bindings for these QObject subclasses can be used in QWidgets applications, but these projects do not provide Rust bindings for QWidgets APIs.

Contributing to CXX-Qt

Clone the Git repository

This repository contains symbolic links, which requires some setup on Windows 10 before cloning the repository. First, enable Windows Developer Mode to avoid needing administrator privileges to create symlinks. Then, enable symlinks in Git:

git config --global core.symlinks true

Now clone the Git repository:

git clone https://github.com/KDAB/cxx-qt.git

Building

Ensure that you have the following installed

• C++ compiler
• clang-format
• CMake
• Qt 5 and/or Qt 6
• Rust toolchain
• mold, lld, or GNU ld.gold for Linux (lld is included in the XCode toolchain on macOS)

This repository's build system uses CMake, which calls Cargo under the hood to build all the examples and tests. One example can be built and run with Cargo directly without using CMake: cargo run -p qml-minimal-no-cmake (this example is also built in the CMake build). This example does not link with GNU ld.bfd which is the default linker on most Linux distributions; installing mold, lld, or GNU ld.gold (from GNU binutils but may be separate package) is required on Linux.

CXX-Qt defaults to building with Qt6. If you want to build with Qt5 when both are installed, add -D USE_QT5=ON to the CMake configure step.

cmake -S . -B build
cmake --build build

Run the basic QML example

./build/examples/qml_minimal/example_qml_minimal

Testing

Testing assumes that cargo clippy and cargo fmt are available, you may need to install these with rustup component add clippy rustfmt.

For testing the book, it assumes that mdbook and mdbook-linkcheck are installed.

For license and memory testing, it assumes that you have reuse installed (eg via pip3 install reuse) and valgrind.

ctest --test-dir build

Licensing

CXX-Qt is Copyright (C) Klarälvdalens Datakonsult AB, and is available under the terms of the MIT or the Apache-2.0 licenses.

Contact KDAB at [email protected] to inquire about additional features or services related to this project.

The following CMake source files are available under the BSD-3-Clause

• cmake/CompilerCaching.cmake - a helper for using sccache

About KDAB

CXX-Qt is supported and maintained by Klarälvdalens Datakonsult AB (KDAB).

The KDAB Group is the global No.1 software consultancy for Qt, C++ and OpenGL applications across desktop, embedded and mobile platforms.

The KDAB Group provides consulting and mentoring for developing Qt applications from scratch and in porting from all popular and legacy frameworks to Qt. We continue to help develop parts of Qt and are one of the major contributors to the Qt Project. We can give advanced or standard trainings anywhere around the globe on Qt as well as C++, OpenGL, 3D and more.

Please visit https://www.kdab.com to meet the people who write code like this.