- Qt 6.8
- Qt Protobuf
- Qt 6.8.3 Reference Documentation

# Qt Protobuf

The Qt Protobuf generator plugin generates Qt-based classes from `.proto` files. You can use the classes to serialize and deserialize their associated protobuf messages.

## Overview

### What are protocol buffers?

Protocol buffers are a language-neutral, platform-neutral, and extensible mechanism for serializing structured data, which is compact and easy to use:

- A user defines the structure of data in `.proto` files.
- Proto compiler is invoked at build time on `.proto` files to generate code in various programming languages.

The provided format is suitable for network traffic or long-term data storage.

### Which problems do protocol buffers solve?

Protocol buffers provide a serialization format for typed and structured data packets up to a few megabytes in size. It allows for the extension with new information without invalidating existing data or requiring code to be updated. For more information, see Protocol Buffers Overview.

### Benefits of using Qt Protobuf

You can use a Protocol buffers mechanism in any Qt-based project:

- Without the need to call a protocol buffer compiler explicitly.
- Without manually integrating generated code into the project tree.
- To access the serialization and deserialization API.
- For integrated properties mechanism for generated protobuf messages.
- For integrated gRPC-client support, see Qt GRPC module.
- For integrated QML-types support for generated protobuf messages.
- For using enabled Qt Core and Qt GUI types as a part of *.proto schema.

## Using the Module

Google protocol buffers provide a generator called `protoc` that supports extensions. The qtprotobufgen Tool is an extension for `protoc` and requires that you install `protoc` on your host system. For more information about the installation, see Protoc Installation.

- Example of installation for Linux, using apt:

       apt install -y protobuf-compiler
       protoc --version  # Ensure compiler version is 3+

- Example of installation for Windows using vcpkg

### QML API

The QML types of the module are available through the QML and QML_URI options in the qt_add_protobuf macro. The import name is equal to the `.proto` package name or defined by QML_URI option in the qt_add_protobuf macro. To use the types, add the following import statement to your .qml file:

     import my.proto.package.uri

### C++ API

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 Protobuf)
     target_link_libraries(mytarget PRIVATE Qt6::Protobuf)

For more details, see the Build with CMake overview.

## Articles and Guides

- CMake Commands in Qt6 Protobuf
- Protobuf Qt Core Types
- Protobuf Qt GUI Types
- Qt Protobuf Well-Known types

## References

- Qt Protobuf C++ Classes
- Qt Protobuf QML Types

## Examples

- Qt Protobuf Examples

## Licenses and Attributions

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

Furthermore, the `qtprotobufgen` tool in Qt 6.8.3 may contain third party modules under the following permissive licenses:

protobuf, version 21.9 | BSD 3-clause "New" or "Revised" License