- Qt 6.6
- Qt Protobuf
- The qtprotobufgen Tool
- Qt 6.6.3 Reference Documentation

# The qtprotobufgen Tool

The `qtprotobufgen` tool can be used to generate Qt Protobuf classes from a protobuf schema. The tool is provided by the CMake `Qt6::ProtobufTools` package. It works as an extension to Google's `protoc` tool.

     find_package(Qt6 COMPONENTS ProtobufTools REQUIRED)

## Usage

Qt provides CMake functions that ease the use of the `qtprotobufgen` tool. When using CMake as a build tool you should prefer using the Qt CMake API. For build systems other than CMake, adapt the commands described in Running manually.

Note: there is no explicit support for building gRPC and Protobuf applications using the Qt GRPC module with qmake.

### CMake

The following CMake commands integrate a protobuf schema into a Qt project.

qt_add_protobuf | Generates Qt-based C++ source code using a protobuf schema

Usually `qtprotobufgen` would be invoked through CMake using the `qt_add_protobuf` macro.

### Using qt_add_protobuf

     cmake_minimum_required(VERSION 3.16...3.22)
     project(MyThings)

     find_package(Qt6 REQUIRED COMPONENTS Protobuf)
     qt_standard_project_setup()

     qt_add_protobuf(MyMessages
         GENERATE_PACKAGE_SUBFOLDERS
         PROTO_FILES
             path/to/message.proto
             path/to/other_message.proto
         PROTO_INCLUDES
             /path/to/proto/include
     )

     qt_add_executable(MyApp main.cpp)

     target_link_libraries(MyApp PRIVATE MyMessages)

In the example above, we generate a library called `MyMessages`, which contains the message types defined in the paths passed to the `PROTO_FILES` option. The `GENERATE_PACKAGE_SUBFOLDERS` option to generate a folder structure for the generated files. And the `PROTO_INCLUDES` option tells protoc to look for dependencies or imports in the specified directories. We create a target for an executable called `MyApp`, which we link to the `MyMessages` library.

### Running manually

     protoc --plugin=protoc-gen-qtprotobuf=<path/to/bin/>qtprotobufgen \
         --qtprotobuf_out="[<options>:]<output_dir>" \
         [--qtprotobuf_opt="<options>"] \
         [-I/extra/proto/include/path] \
         <protofile>.proto

The `options` argument is a semicolon-separated list of Options. It can be passed in two different ways. Either by prepending to the options to the output_dir argument, delimited by a colon. Or through a separate argument, `--qtprotobuf_opt`. You also can pass the corresponding keys as the `QT_PROTOBUF_OPTIONS` environment variable. Keys need to be presented as a semicolon-separated list:

     export QT_PROTOBUF_OPTIONS="COPY_COMMENTS;GENERATE_PACKAGE_SUBFOLDERS;EXTRA_NAMESPACE=MyTopLevelNamespace"

### Options

The generator supports options that can be provided to tune generation. Options have direct aliases in the qt_add_protobuf function. The following options are supported:

- `COPY_COMMENTS` copies comments from `.proto` files. If provided in the parameter list, comments related to messages and fields are copied to generated header files.
- `GENERATE_PACKAGE_SUBFOLDERS` generates a folder structure for the generated files matching the `.proto` file's package name. For example, `package io.qt.test;` would put the generated files into `io/qt/test/`.
- `EXTRA_NAMESPACE` is an optional namespace that will be used for the generated classes. The classes are always generated in a namespace whose name is the same as the package name specified in the `.proto` file. If this option is used, then everything will be nested inside the extra namespace.
- `EXPORT_MACRO` is the base name of the symbol export macro used for the generated code. The generated macro name is constructed as `QPB_<EXPORT_MACRO>_EXPORT`. If the option is not set, the macro is not generated.
- `QML_URI` enables QProtobufMessage types in the QML context by registering them in a QML module via the provided `URI` import path. The `URI` option will be used in the line of the generated `qmldir` file, and also used to form the target path by replacing dots with forward slashes.

  Note: Read Identified Modules for further in-depth discussion of the `URI`.