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"
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 the.protofiles into the generated code.GENERATE_PACKAGE_SUBFOLDERSuses the package name specifier from the.protofiles 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_MACROdefines the base name for the export macro used in the generated code. The final macro name is constructed asQPB_<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.
HEADER_GUARDspecifies the mechanism used for guarding generated header files from multiple inclusion. Possible values arepragma,filename. Defaults tofilename. Setting the option topragmagenerates the modern pragma header guard:#pragma once ...
Omitting the option or setting the option to
filenamegenerates theifdefwrapping guard, and uses the '.proto' filename as the guard infix:#ifdef MYMESSAGES_QPB_H #define MYMESSAGES_QPB_H ... #endif // MYMESSAGES_QPB_H
Select the preferred guard style according to your project structure.