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.

CMake

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

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"

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 the .proto files into the generated code.
• GENERATE_PACKAGE_SUBFOLDERS uses the package name specifier from the .proto files to create the folder structure for the generated files. For example, if the package is defined as: package io.qt.test, the generated files will be placed in OUTPUT_DIRECTORY/io/qt/test/.
• EXPORT_MACRO defines the base name for the export macro used in the generated code. The final macro name is constructed as QPB_<EXPORT_MACRO>_EXPORT. If this option is not set, no export macro is generated.

  Since Qt 6.8, the following format is supported: EXPORT_MACRO=macro_name[:macro_output_file[:<true|false>]]. This format allows you to specify the name of the header file containing the export macro and explicitly control whether it is generated.

  Note: If <macro_output_file> is not provided, the option defaults to the previous syntax.