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.
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_COMMENTScopies comments from.protofiles. If provided in the parameter list, comments related to messages and fields are copied to generated header files.GENERATE_PACKAGE_SUBFOLDERSgenerates a folder structure for the generated files matching the.protofile's package name. For example,package io.qt.test;would put the generated files intoio/qt/test/.EXTRA_NAMESPACEis 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.protofile. If this option is used, then everything will be nested inside the extra namespace.EXPORT_MACROis the base name of the symbol export macro used for the generated code. The generated macro name is constructed asQPB_<EXPORT_MACRO>_EXPORT. If the option is not set, the macro is not generated.QML_URIenables QProtobufMessage types in the QML context by registering them in a QML module via the providedURIimport path. TheURIoption will be used in the line of the generatedqmldirfile, 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.