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MIT-licensed Qt 6 bindings for Zig

This library is a straightforward binding of the Qt 6.4+ API. You must have a working Qt 6 C++ development toolchain to use this binding. The Building section below has instructions for installing the required dependencies.

This library is designed to be used as a dependency in a larger application and not as a standalone library. The versioning scheme used by this library is based on the Qt version used to generate the bindings with an additional nod to the library revision number. Any breaking changes to the library will be reflected in the changelog.

These bindings are based on the MIQT bindings for Go that were released in 2024. The bindings are complete for QtCore, QtGui, QtWidgets, QtMultimedia, QtMultimediaWidgets, QtSpatialAudio, QtPrintSupport, QtSvg, QtNetwork, QtWebChannel, QtWebEngine, QScintilla, and others. There is support for slots/signals, subclassing, custom widgets, async via Qt, etc., but the bindings may be immature or unstable in some ways. It is fairly easy to encounter segmentation faults with improper handling. Q3 of the FAQ is a decent entry point for newcomers. Please try out the library and start a discussion if you have any questions or issues relevant to this library.

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TABLE OF CONTENTS

• Supported Platforms
• License
• Examples
• Building
• Usage
• FAQ
• Special Thanks

Supported platforms

OS	Arch	Linkage (Bindings)	Status
FreeBSD	x86_64	Static	✅ Works
Linux	arm64	Static	✅ Works
Linux	x86_64	Static	✅ Works

License

The libqt6zig bindings are licensed under the MIT license.

You must also meet your Qt license obligations.

Examples

The helloworld example follows:

const std = @import("std");
const qt6 = @import("libqt6zig");
const qapplication = qt6.qapplication;
const qpushbutton = qt6.qpushbutton;
const qwidget = qt6.qwidget;

var counter: isize = 0;

pub fn main() void {
    // Initialize Qt application
    const argc = std.os.argv.len;
    const argv = std.os.argv.ptr;
    _ = qapplication.New(argc, argv);

    const text = "Hello world!";
    const widget = qwidget.New2();
    if (widget == null) @panic("Failed to create widget");
    defer qwidget.QDelete(widget);

    // We don't need to free the button, it's a child of the widget
    const button = qpushbutton.New5(text, widget);
    qpushbutton.SetFixedWidth(button, 320);

    qpushbutton.OnClicked(button, button_callback);

    qwidget.Show(widget);

    _ = qapplication.Exec();

    std.debug.print("OK!\n", .{});
}

fn button_callback(self: ?*anyopaque) callconv(.c) void {
    counter += 1;
    var buffer: [64]u8 = undefined;
    const text = "You have clicked the button {} time(s)";
    const formatted = std.fmt.bufPrintZ(&buffer, text, .{counter}) catch @panic("Failed to bufPrintZ");
    qpushbutton.SetText(self, formatted);
}

Full examples are available in the libqt6zig-examples repository.

Building

FreeBSD (native)

• Tested with FreeBSD 14 / Qt 6.8

For dynamic linking with the Qt 6 system libraries:

sudo pkg install qt6-base qt6-multimedia qt6-svg qt6-webchannel qt6-webengine qscintilla2-qt6 zig

NOTE The zig package may need to be downloaded or compiled and installed separately if the latest stable version is not available in the default repositories.

Linux (native)

• Tested with Debian 12 + 13 / Qt 6.4 + 6.7

• Tested with Linux Mint 22 / Qt 6.4

• Tested with Ubuntu 24.04 / Qt 6.4

• Tested with Fedora 41 / Qt 6.8

• Tested with EndeavourOS Mercury / Qt 6.8

For dynamic linking with the Qt 6 system libraries:

• Debian-based distributions:

sudo apt install qt6-base-dev libqscintilla2-qt6-dev qt6-base-private-dev qt6-multimedia-dev qt6-svg-dev qt6-webchannel-dev qt6-webengine-dev

NOTE The zig package must be downloaded and installed separately.

• Fedora-based distributions:

sudo dnf install qt6-qtbase-devel qscintilla-qt6-devel qt6-qtmultimedia-devel qt6-qtsvg-devel qt6-qtwebchannel-devel qt6-qtwebengine-devel zig

NOTE The zig package will need to be downloaded and installed separately if the latest stable version is not available in the default repositories.

• Arch-based distributions:

sudo pacman -S qt6-base qscintilla-qt6 qt6-multimedia qt6-svg qt6-webchannel qt6-webengine zig

Once the required packages are installed, the library can be built from the root of the repository:

zig build

Users of Arch-based distributions need to make sure that all packages are up-to-date first and will need to add the following option to support successful compilation:

zig build -Denable-workaround=true

The compiled libraries can be installed to the system in a non-default location by adding the --prefix-lib-dir option to the build command:

sudo zig build --prefix-lib-dir /usr/local/lib/libqt6zig # creates /usr/local/lib/libqt6zig/{libraries}

To skip the restricted extras:

zig build -Dskip-restricted=true

To see the full list of build options available:

zig build --help

Usage

• Import the library into your project:

zig fetch --save git+https://github.com/rcalixte/libqt6zig

Append #<tag>, #<commit>, or #<branch> to the end of the URL to pin to a specific version of the library.

• Add the library to your build.zig file:

const qt6zig = b.dependency("libqt6zig", .{
    .target = target,
    .optimize = .ReleaseFast,
});

// After defining the executable, add the module from the library
exe.root_module.addImport("libqt6zig", qt6zig.module("libqt6zig"));

// Link the compiled libqt6zing libraries to the executable
// qt_lib_name is the name of the target library without prefix and suffix, e.g. qapplication, qwidget, etc.
exe.root_module.linkLibrary(qt6zig.artifact(qt_lib_name));

Extra options are required for building on Arch-based distributions. Refer to the build system at the examples link below for more details.

• Use the library in your code:

// the main qt6 module to import
const qt6 = @import("libqt6zig");

// C ABI Qt typedefs (if needed)
const C = qt6.C;

// Qt class imports for Zig
const qapplication = qt6.qapplication;
const qwidget = qt6.qwidget;
const qnamespace_enums = qt6.qnamespace_enums;

Full examples of the build system and sample applications can be found in the libqt6zig-examples repository. Cross-compilation is not supported by this library at this time.

FAQ

Q1. Can I release a proprietary, commercial app with this binding?

Yes. You must also meet your Qt license obligations: either dynamically link Qt library files under the LGPL or purchase a Qt commercial license for static linking.

Q2. How long does it take to compile?

Under normal conditions, the first compilation should take less than 10 minutes, assuming the hardware in use is at or above the level of that of a consumer-grade mid-tier machine released in the past decade. Once the build cache is warmed up, subsequent compilations should be very fast, on the order of seconds.

Q3. How does the libqt6zig API differ from the official Qt C++ API?

Supported Qt C++ class methods are implemented 1:1 as structs of functions where the function names in Zig correspond to the PascalCase equivalent of the Qt C++ method and the struct names are lowercase equivalents of the Qt C++ class name. The official Qt documentation should be used for reference and is included in the library wrapper source code (though not all links are guaranteed to work perfectly, nor is this functionality in scope for this project).

• QWidget::show() is projected as qwidget.Show(?*anyopaque)
• QPushButton::setText(QString) is projected as qpushbutton.SetText(?*anyopaque, []const u8)

As a mental model, developers consuming this library should keep in mind that there are essentially two different tracks of memory management required for clean operation: one for the C++ side and one for the Zig side. The Zig side is managed by the developer and the C++ side has variant ownership semantics. Ownership semantics are documented throughout the C++ documentation.

There are bits of idiomatic Zig in the library in the form of allocators as parameters to functions but much of the code is not idiomatic for Zig due to the complexity of the Qt C++ API. Knowledge of the Qt C++ API is required to understand and make full use of the library. While not an exhaustive list, there are some key topics to understand:

• Qt object ownership
• Qt signals and slots
• Qt's property system
• Qt's Meta-Object system
• Qt widgets

The QByteArray, QString, QList<T>, QVector<T>, QMap<K,V>, QHash<K,V> types are projected as plain Zig types: []u8, []const u8, []T, AutoHashMapUnmanaged[K]V, and StringHashMapUnmanaged[V]. Therefore, it is not possible to call any of the Qt type's methods and some Zig equivalent method must be used instead. (The raw C ABI is also available due to the headers being required to define Qt types in Zig, but it is not recommended for use beyond Qt class type definitions where needed.) This library was constructed with the goal of enabling single-language application development. Anything beyond that boundary is up to the developer to implement.

• Zig string types are internally converted to QString using QString::fromUtf8. Therefore, the Zig string input must be UTF-8 to avoid mojibake. If the Zig input string contains binary data, the conversion would corrupt such bytes into U+FFFD (�). On return to Zig space, this becomes \xEF\xBF\xBD.

• The iteration order of a Qt QMap/QHash will differ from the Zig API map iteration order. QMap is iterated by key order, but the Zig maps used by the library and QHash iterate in an undefined internal order. Future versions of libqt6zig may provide a way to iterate in a specific order.

There is a helper library that contains some types and functions that are useful for the C ABI but these are not required for the Zig API.

Where Qt returns a C++ object by value (e.g. QSize), the binding may have moved it to the heap, and in Zig, this may be represented as a pointer type. In such cases, the caller is the owner and must free the object (using either QDelete methods for the type or deallocating or destroying via the allocators). This means code using libqt6zig can look similar to the Qt C++ equivalent code but with the addition of proper memory management.

The connect(targetObject, targetSlot) methods are projected as On(targetObject, fn() callconv(.c)...). While the parameters in the methods themselves are more convenient to use, the documentation comments in the Zig source code should be used for reference for the proper usage of the parameter types and Qt vtable references. The example code above includes a simple callback function that can be used as a reference.

• You can also override virtual methods like PaintEvent in the same way. Where supported, there are additional On and QBase variants:
  • OnPaintEvent: Set an override callback function to be called when PaintEvent is invoked. For certain methods, even with the override set, the base class implementation can still be called by Qt internally and these calls can not be prevented.
  • QBasePaintEvent: Invoke the base class implementation of PaintEvent. This is useful for when the custom implementation requires the base class implementation. (When there is no override set, the QBase implementation is equivalent to PaintEvent.)

Qt class inherited types are projected via opaque pointers and @ptrCast in Zig. For example, to pass a var myLabel: ?*QLabel to a function taking only the ?*QWidget base class, it should be sufficient to pass myLabel and the library will automatically cast it to the correct type and Qt vtable reference.

• When a Qt subclass adds a method overload (e.g. QMenu::sizeHint(QMenu*) vs QWidget::sizeHint(QWidget*)), the base class version is shadowed and can only be called via qwidget.SizeHint(?*anyopaque) while the subclass implementation can be called directly, e.g. qmenu.SizeHint(?*anyopaque). Inherited methods are shadowed for convenience as well, e.g. qmenu.Show(?*anyopaque) is equivalent to qwidget.Show(?*anyopaque). While the library aims to simplify usage, consideration should still be given to the Qt documentation for the proper usage of the parameter types and Qt vtable references.

Qt expects fixed OS threads to be used for each QObject. When you first call qapplication.New, that will be considered the Qt main thread.

• When accessing Qt objects from inside another thread, it's safest to use Threading.Async() (from this library) to access the Qt objects from Qt's main thread. The Threading library documents additional available strategies within the source code.

Qt C++ enums are projected as Zig enum structs of i32 or i64 values with the same names. For example, Qt::AlignmentFlag is projected as enums.AlignmentFlag within the libqnamespace module and exported by default as qnamespace_enums.AlignmentFlag though developers are free to use whatever naming convention they prefer for imports. Enums are currently defined as either i32 or i64 (where necessary) in the Zig API and as i64 when expected as a parameter or returned as a type by the Zig API.

Some C++ idioms that were difficult to project were omitted from the binding. This can be improved in the future.

Q4. What build modes are supported by the library?

Currently, only ReleaseFast, ReleaseSafe, and ReleaseSmall are supported. The Debug build mode is not supported. This may change in the future. The default build mode is ReleaseFast. To change the build mode:

zig build -Doptimize=ReleaseSafe

Q5. Can I use Qt Designer and the Qt Resource system?

MIQT (the upstream Qt bindings for Go) has a custom implementation of Qt uic and rcc tools, to allow using Qt Designer for form design and resource management. There is work in progress to support Qt Designer with this library in the future.

Q6. How can I add bindings for another Qt library?

Fork this repository and add your library to the genbindings/config-libraries file. Read more »

Special Thanks

• @mappu for the MIQT bindings that provided the phenomenal foundation for this project

• @arnetheduck for proving the value of collaboration on the back-end of this project while working across different target languages