Protobuf Code Generation - 使用Protobuf的代码生成

Introduction - 简介

本示例展示如何使用 protobuf 生成源码文件。Protocol Buffers 是一种由谷歌提出的数据序列化的格式。用户可以提供一个描述了数据的 .proto 格式的文件，通过protobuf编译器，这一文件可以被编译成包括C++在内的一系列编程语言的源码文件。

This example shows how to generate source files using https://github.com/google/protobuf[protobuf].
Protocol Buffers is a data serialization format from Google. A user provides a
`.proto` file with a description of the data. Then using the protobuf compiler, the proto file
can be translated into source code in a number of languages including C++.

本教程的目录结构如下所示：

The files in this tutorial are below:
$ tree
.
├── AddressBook.proto
├── CMakeLists.txt
├── main.cpp

Requirements - 必要依赖

本示例要求预安装protocol buffers的二进制文件和库文件，在Ubuntu系统中，可以使用下述命令安装：

This example requires the protocol buffers binary and libraries to be installed.
This can be installed on Ubuntu using
sudo apt-get install protobuf-compiler libprotobuf-dev

解析

Exported Variables - 导出变量

在本示例中，通过CMake protobuf包到处并使用的变量如下：

The variables exported by the CMake protobuf package and used in this example include:

  • PROTOBUF_FOUND - 标志Protocol Buffers是否安装

    • PROTOBUF_FOUND - If Protocol Buffers is installed

  • PROTOBUF_INCLUDE_DIRS - 描述protobuf头文件路径

    • PROTOBUF_INCLUDE_DIRS - The protobuf header files

  • PROTOBUF_LIBRARIES - 描述protobuf库文件路径

    • PROTOBUF_LIBRARIES - The protobuf library

关于Protobuf变量更详细的描述可以查阅 FindProtobuf.cmake 文件获取。

More variables are defined and can be found by examining the documentation at the
top of your `FindProtobuf.cmake` file.

Generating Source - 源文件生成

CMake protobuf包中包含了一些列的帮助函数来简化源代码生成流程，在本示例中，我们是用下面的语句来生成C++源码：

 The protobuf CMake package includes a number of helper functions to make the
 code generation easier. In this example we are generating C++ source and use
the following code:
PROTOBUF_GENERATE_CPP(PROTO_SRCS PROTO_HDRS AddressBook.proto)

这里的参数包括：

The arguments are:

  • PROTO_SRCS - 将被存储在.pb.cc文件里的变量名

    • PROTO_SRCS - Name of the variable that will store the .pb.cc files.

  • PROTO_HDRS- 将被存储在.pb.h文件里的变量名

    • PROTO_HDRS- Name of the variable that will store the .pb.h files.

  • AddressBook.proto - 用于编译的原始.proto文件

    • AddressBook.proto - The .proto file to generate code from.

Generated Files - 文件生成

在调用过 PROTOBUF_GENERATE_CPP 函数之后，上述变量便可以被使用了，他们将被视为protobuf编译器执行特定命令生成的输出结果。

After the `PROTOBUF_GENERATE_CPP` function is called, you will have the above
mentioned variables available. These will be marked as the output to a custom command
which calls the protobuf compiler binary to generate them.

为了进一步完成文件的生成，你需要将他们添加进库函数或者可执行文件中，例如：

To then have the files generated you should add them to a library or executable.
For example:
add_executable(protobuf_example
    main.cpp
    ${PROTO_SRCS}
    ${PROTO_HDRS})

这使得 make 这一命令被调用时，protobuf编译器也将随之被调用。

This will cause the protobuf compiler to be called when you call `make` on that
executables target.

当.proto文件被改变时，与其相关联的源代码文件也将被自动重新生成；不过，如果.proto文件没有发生修改，重新执行 make 命令，并不会发生任何变化。

When changes are made to the .proto file, the associated source files will be
autogenerated again. However, if no changes are made to the .proto file and you re-run
make, then nothing will be done.

Building the Example - 构建示例

$ mkdir build

$ cd build/

$ cmake ..
-- The C compiler identification is GNU 4.8.4
-- The CXX compiler identification is GNU 4.8.4
-- Check for working C compiler: /usr/bin/cc
-- Check for working C compiler: /usr/bin/cc -- works
-- Detecting C compiler ABI info
-- Detecting C compiler ABI info - done
-- Check for working CXX compiler: /usr/bin/c++
-- Check for working CXX compiler: /usr/bin/c++ -- works
-- Detecting CXX compiler ABI info
-- Detecting CXX compiler ABI info - done
-- Looking for include file pthread.h
-- Looking for include file pthread.h - found
-- Looking for pthread_create
-- Looking for pthread_create - not found
-- Looking for pthread_create in pthreads
-- Looking for pthread_create in pthreads - not found
-- Looking for pthread_create in pthread
-- Looking for pthread_create in pthread - found
-- Found Threads: TRUE
-- Found PROTOBUF: /usr/lib/x86_64-linux-gnu/libprotobuf.so
protobuf found
PROTO_SRCS = /home/matrim/workspace/cmake-examples/03-code-generation/protobuf/build/AddressBook.pb.cc
PROTO_HDRS = /home/matrim/workspace/cmake-examples/03-code-generation/protobuf/build/AddressBook.pb.h
-- Configuring done
-- Generating done
-- Build files have been written to: /home/matrim/workspace/cmake-examples/03-code-generation/protobuf/build

$ ls
CMakeCache.txt  CMakeFiles  cmake_install.cmake  Makefile

$ make VERBOSE=1
/usr/bin/cmake -H/home/matrim/workspace/cmake-examples/03-code-generation/protobuf -B/home/matrim/workspace/cmake-examples/03-code-generation/protobuf/build --check-build-system CMakeFiles/Makefile.cmake 0
/usr/bin/cmake -E cmake_progress_start /home/matrim/workspace/cmake-examples/03-code-generation/protobuf/build/CMakeFiles /home/matrim/workspace/cmake-examples/03-code-generation/protobuf/build/CMakeFiles/progress.marks
make -f CMakeFiles/Makefile2 all
make[1]: Entering directory `/home/matrim/workspace/cmake-examples/03-code-generation/protobuf/build'
make -f CMakeFiles/protobuf_example.dir/build.make CMakeFiles/protobuf_example.dir/depend
make[2]: Entering directory `/home/matrim/workspace/cmake-examples/03-code-generation/protobuf/build'
/usr/bin/cmake -E cmake_progress_report /home/matrim/workspace/cmake-examples/03-code-generation/protobuf/build/CMakeFiles 1
[ 33%] Running C++ protocol buffer compiler on AddressBook.proto
/usr/bin/protoc --cpp_out /home/matrim/workspace/cmake-examples/03-code-generation/protobuf/build -I /home/matrim/workspace/cmake-examples/03-code-generation/protobuf /home/matrim/workspace/cmake-examples/03-code-generation/protobuf/AddressBook.proto
cd /home/matrim/workspace/cmake-examples/03-code-generation/protobuf/build && /usr/bin/cmake -E cmake_depends "Unix Makefiles" /home/matrim/workspace/cmake-examples/03-code-generation/protobuf /home/matrim/workspace/cmake-examples/03-code-generation/protobuf /home/matrim/workspace/cmake-examples/03-code-generation/protobuf/build /home/matrim/workspace/cmake-examples/03-code-generation/protobuf/build /home/matrim/workspace/cmake-examples/03-code-generation/protobuf/build/CMakeFiles/protobuf_example.dir/DependInfo.cmake --color=
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Scanning dependencies of target protobuf_example
make[2]: Leaving directory `/home/matrim/workspace/cmake-examples/03-code-generation/protobuf/build'
make -f CMakeFiles/protobuf_example.dir/build.make CMakeFiles/protobuf_example.dir/build
make[2]: Entering directory `/home/matrim/workspace/cmake-examples/03-code-generation/protobuf/build'
/usr/bin/cmake -E cmake_progress_report /home/matrim/workspace/cmake-examples/03-code-generation/protobuf/build/CMakeFiles 2
[ 66%] Building CXX object CMakeFiles/protobuf_example.dir/main.cpp.o
/usr/bin/c++    -I/home/matrim/workspace/cmake-examples/03-code-generation/protobuf/build    -o CMakeFiles/protobuf_example.dir/main.cpp.o -c /home/matrim/workspace/cmake-examples/03-code-generation/protobuf/main.cpp
/usr/bin/cmake -E cmake_progress_report /home/matrim/workspace/cmake-examples/03-code-generation/protobuf/build/CMakeFiles 3
[100%] Building CXX object CMakeFiles/protobuf_example.dir/AddressBook.pb.cc.o
/usr/bin/c++    -I/home/matrim/workspace/cmake-examples/03-code-generation/protobuf/build    -o CMakeFiles/protobuf_example.dir/AddressBook.pb.cc.o -c /home/matrim/workspace/cmake-examples/03-code-generation/protobuf/build/AddressBook.pb.cc
Linking CXX executable protobuf_example
/usr/bin/cmake -E cmake_link_script CMakeFiles/protobuf_example.dir/link.txt --verbose=1
/usr/bin/c++       CMakeFiles/protobuf_example.dir/main.cpp.o CMakeFiles/protobuf_example.dir/AddressBook.pb.cc.o  -o protobuf_example -rdynamic -lprotobuf -lpthread
make[2]: Leaving directory `/home/matrim/workspace/cmake-examples/03-code-generation/protobuf/build'
/usr/bin/cmake -E cmake_progress_report /home/matrim/workspace/cmake-examples/03-code-generation/protobuf/build/CMakeFiles  1 2 3
[100%] Built target protobuf_example
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$ make VERBOSE=1
/usr/bin/cmake -H/home/matrim/workspace/cmake-examples/03-code-generation/protobuf -B/home/matrim/workspace/cmake-examples/03-code-generation/protobuf/build --check-build-system CMakeFiles/Makefile.cmake 0
/usr/bin/cmake -E cmake_progress_start /home/matrim/workspace/cmake-examples/03-code-generation/protobuf/build/CMakeFiles /home/matrim/workspace/cmake-examples/03-code-generation/protobuf/build/CMakeFiles/progress.marks
make -f CMakeFiles/Makefile2 all
make[1]: Entering directory `/home/matrim/workspace/cmake-examples/03-code-generation/protobuf/build'
make -f CMakeFiles/protobuf_example.dir/build.make CMakeFiles/protobuf_example.dir/depend
make[2]: Entering directory `/home/matrim/workspace/cmake-examples/03-code-generation/protobuf/build'
/usr/bin/cmake -E cmake_progress_report /home/matrim/workspace/cmake-examples/03-code-generation/protobuf/build/CMakeFiles 1
[ 33%] Running C++ protocol buffer compiler on AddressBook.proto
/usr/bin/protoc --cpp_out /home/matrim/workspace/cmake-examples/03-code-generation/protobuf/build -I /home/matrim/workspace/cmake-examples/03-code-generation/protobuf /home/matrim/workspace/cmake-examples/03-code-generation/protobuf/AddressBook.proto
cd /home/matrim/workspace/cmake-examples/03-code-generation/protobuf/build && /usr/bin/cmake -E cmake_depends "Unix Makefiles" /home/matrim/workspace/cmake-examples/03-code-generation/protobuf /home/matrim/workspace/cmake-examples/03-code-generation/protobuf /home/matrim/workspace/cmake-examples/03-code-generation/protobuf/build /home/matrim/workspace/cmake-examples/03-code-generation/protobuf/build /home/matrim/workspace/cmake-examples/03-code-generation/protobuf/build/CMakeFiles/protobuf_example.dir/DependInfo.cmake --color=
Dependee "/home/matrim/workspace/cmake-examples/03-code-generation/protobuf/build/CMakeFiles/protobuf_example.dir/DependInfo.cmake" is newer than depender "/home/matrim/workspace/cmake-examples/03-code-generation/protobuf/build/CMakeFiles/protobuf_example.dir/depend.internal".
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Scanning dependencies of target protobuf_example
make[2]: Leaving directory `/home/matrim/workspace/cmake-examples/03-code-generation/protobuf/build'
make -f CMakeFiles/protobuf_example.dir/build.make CMakeFiles/protobuf_example.dir/build
make[2]: Entering directory `/home/matrim/workspace/cmake-examples/03-code-generation/protobuf/build'
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/usr/bin/cmake -E cmake_progress_report /home/matrim/workspace/cmake-examples/03-code-generation/protobuf/build/CMakeFiles 3
[100%] Building CXX object CMakeFiles/protobuf_example.dir/AddressBook.pb.cc.o
/usr/bin/c++    -I/home/matrim/workspace/cmake-examples/03-code-generation/protobuf/build    -o CMakeFiles/protobuf_example.dir/AddressBook.pb.cc.o -c /home/matrim/workspace/cmake-examples/03-code-generation/protobuf/build/AddressBook.pb.cc
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/usr/bin/cmake -E cmake_link_script CMakeFiles/protobuf_example.dir/link.txt --verbose=1
/usr/bin/c++       CMakeFiles/protobuf_example.dir/main.cpp.o CMakeFiles/protobuf_example.dir/AddressBook.pb.cc.o  -o protobuf_example -rdynamic -lprotobuf -lpthread
make[2]: Leaving directory `/home/matrim/workspace/cmake-examples/03-code-generation/protobuf/build'
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$ ls
AddressBook.pb.cc  CMakeCache.txt  cmake_install.cmake  protobuf_example
AddressBook.pb.h   CMakeFiles      Makefile

$ ./protobuf_example test.db
test.db: File not found.  Creating a new file.
Enter person ID number: 11
Enter name: John Doe
Enter email address (blank for none): wolly@sheep.ie
Enter a phone number (or leave blank to finish):

$ ls
AddressBook.pb.cc  CMakeCache.txt  cmake_install.cmake  protobuf_example
AddressBook.pb.h   CMakeFiles      Makefile             test.db

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