- Qt 6.5
- Qt Bluetooth
- Qt 6.5.2 Reference Documentation

# Qt Bluetooth

The Bluetooth API provides connectivity between Bluetooth enabled devices.

Currently, the API is supported on the following platforms:

API Feature | Android | iOS | Linux (BlueZ 5.x) | macOS | Windows
--- | --- | --- | --- | --- | ---
Classic Bluetooth | x |  | x | x | x
Bluetooth LE Central | x | x | x | x | x
Bluetooth LE Peripheral | x | x | x | x |

## Overview

Bluetooth is a short-range (less than 100 meters) wireless technology. It has a data transfer rate of 2.1 Mbps, which makes it ideal for transferring data between devices. Bluetooth connectivity is based on basic device management, such as scanning for devices, gathering information about them, and exchanging data between them.

Qt Bluetooth supports Bluetooth Low Energy development for client/central role use cases. Further details can be found in the Bluetooth Low Energy Overview section.

## Using the Module

Using a Qt module's C++ API requires linking against the module library, either directly or through other dependencies. Several build tools have dedicated support for this, including CMake and qmake.

### Building with CMake

Use the `find_package()` command to locate the needed module component in the `Qt6` package:

     find_package(Qt6 REQUIRED COMPONENTS Bluetooth)
     target_link_libraries(mytarget PRIVATE Qt6::Bluetooth)

For more details, see the Build with CMake overview.

### Building with qmake

To configure the module for building with qmake, add the module as a value of the `QT` variable in the project's .pro file:

     QT += bluetooth

## Related Information

### Building Qt Bluetooth

Even though the module can be built for all Qt platforms, the module is not ported to all of them. Non-supported platforms employ a dummy backend that is automatically selected when the platform is not supported. The dummy backend reports appropriate error messages and values, which enables you to detect at runtime that the current platform is not supported. The dummy backend is also selected on Linux if BlueZ development headers are not found during build time or Qt was built without Qt D-Bus support.

The usage of the dummy backend is highlighted via an appropriate warning while building and running.

#### Linux Specific

Since Qt 6.5 the Linux peripheral support has two backend alternatives: BlueZ DBus and Bluetooth kernel API. The Bluez DBus backend introduced in Qt 6.5 is intended as the eventual successor of the lower abstraction level kernel backend.

The BlueZ DBus API is more limited in terms of features and is therefore not the default backend for compatibility reasons.

The BlueZ DBus backend can be configured to use by setting the QT_BLUETOOTH_USE_DBUS_PERIPHERAL environment variable. The QLowEnergyController peripheral instantiation then introspects the presence of BlueZ DBus peripheral APIs on the local bluetooth adapter. The minimum version requirement for BlueZ is 5.56.

One noteworthy difference is that with BlueZ DBus peripheral backend the user process no longer needs to have the CAP_NET_ADMIN capability (eg. run as root).

#### macOS Specific

The Bluetooth API on macOS requires a certain type of event dispatcher that in Qt causes a dependency to QGuiApplication. However, you can set the environment variable `QT_EVENT_DISPATCHER_CORE_FOUNDATION=1` to circumvent this issue.

Applications that don't use Classic Bluetooth will find a subset of QtBluetooth is available, as CoreBluetooth (Bluetooth LE) don't require QApplication or QGuiApplication.

### Articles and Guides

- Classic Bluetooth Overview
- Bluetooth Low Energy Overview

### Reference

- C++ Classes

### Logging Categories

The QtBluetooth module exports the following logging categories:

Logging Category | Description
--- | ---
qt.bluetooth | Enables logging of cross platform code path in QtBluetooth
qt.bluetooth.android | Enables logging of the Android implementation
qt.bluetooth.bluez | Enables logging of the BLuez/Linux implementation
qt.bluetooth.ios | Enables logging of the iOS implementation
qt.bluetooth.osx | Enables logging of the macOS implementation
qt.bluetooth.windows | Enables logging of the Windows implementation

Logging categories enable additional warning and debug output for QtBluetooth. More detailed information about logging is found in QLoggingCategory. A quick way to enable all QtBluetooth logging is to add the following line to the `main()` function:

     QLoggingCategory::setFilterRules(QStringLiteral("qt.bluetooth* = true"));

### Examples

- QML
  - Bluetooth Low Energy Heart Rate Game
  - Bluetooth Low Energy Heart Rate Server
  - Bluetooth Low Energy Scanner
- C++
  - Bluetooth Chat

## Module Evolution

Changes to Qt Bluetooth lists important changes in the module API and functionality that were done for the Qt 6 series of Qt.

## Licenses and Attributions

Qt Bluetooth is available under commercial licenses from The Qt Company. In addition, it is available under the GNU Lesser General Public License, version 3, or the GNU General Public License, version 2. See Qt Licensing for further details.

On Linux, Qt Bluetooth uses a separate executable, `sdpscanner`, to integrate with the official Linux bluetooth protocol stack BlueZ. BlueZ is available under the GNU General Public License, version 2.

BlueZ | GNU General Public License v2.0 only (This does not force user code to be GPL'ed. For more info see details.)