CMake Commands in Qt6 Protobuf

You should call the following CMake commands to use the Qt6::Protobuf module in your project:

 find_package(Qt6 REQUIRED COMPONENTS Protobuf)

 target_link_libraries(mytarget PRIVATE Qt6::Protobuf)

You can use the qt_add_protobuf CMake command to implicitly call Qt Protobuf code generation for your project.

The macros usage examples:

 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.

QML extended protobuf example

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

 find_package(Qt6 REQUIRED COMPONENTS Protobuf Quick)
 qt_standard_project_setup()

 qt_add_protobuf(MyMessagesPlugin
     QML
     QML_URI my.messages.module.uri
     PROTO_FILES
         path/to/message.proto
         path/to/other_message.proto
     PROTO_INCLUDES
         /path/to/proto/include
 )

 qt_add_protobuf(MyApp
     QML
     PROTO_FILES
         path/to/internal_message.proto
     PROTO_INCLUDES
         /path/to/proto/include
 )

 qt_add_qml_module(MyApp
     URI example.uri
     VERSION 1.0
     QML_FILES qml/main.qml
 )

 qt_add_executable(MyApp main.cpp)
 target_link_libraries(MyApp PRIVATE Quick)

In the QML extended example above, by the first qt_add_protobuf call, we generate a QML module called MyMessagesPlugin, which contains the message types defined in the paths passed to the PROTO_FILES option. We use the QML option, that enables proto message types registration in the QML context. The registered types will be available in QML by importing a path that is set by the QML_URI. By second qt_add_protobuf call we add auto-generated code into the existing MyApp QML module. The QML_URI is not required in such cases. Finally, we create a target for an executable called MyApp, which has a QML module for the graphical part and loads MyMessagesPlugin into the main.qml file via the my.messages.module.uri import.

Installing standalone Qt Protobuf library

The qt_add_protobuf command also produces lists of artifacts for further installation. You can read these artifacts by specifying OUTPUT_HEADERS, and OUTPUT_TARGETS arguments as follows:

 qt_add_protobuf(MyProtoLib
     PROTO_FILES
         mylib.proto
     OUTPUT_HEADERS
         public_headers
     OUTPUT_TARGETS
         generated_targets
 )

The command stores the list of the header files and targets produced by the qt_add_protobuf command to the public_headers and generated_targets variables accordingly.

Use the standard CMake install command to install the artifacts and generate the config files for your library:

 include(GNUInstallDirs)
 set_target_properties(MyProtoLib PROPERTIES
     PUBLIC_HEADER
         "${public_headers}"
     INTERFACE_INCLUDE_DIRECTORIES
         "$<INSTALL_INTERFACE:${CMAKE_INSTALL_PREFIX}/${CMAKE_INSTALL_INCLUDEDIR}>"
 )
 install(TARGETS ${generated_targets} EXPORT MyProtoLibTargets
     PUBLIC_HEADER
         DESTINATION "${CMAKE_INSTALL_INCLUDEDIR}"
 )
 install(EXPORT MyProtoLibTargets NAMESPACE MyProtoLib:: DESTINATION lib/cmake/MyProtoLib)

Then use the generated MyProtoLibTargets config in the package config file. You can read more about the package creation process in the official CMake documentation.

After installation the library is available as the standalone CMake package:

 find_package(Qt6 COMPONENTS Protobuf)
 find_package(MyProtoLib CONFIG)

 add_executable(MyApp main.cpp)
 target_link_libraries(MyApp PRIVATE MyProtoLib::MyProtoLib Qt6::Protobuf)