Cxxproject

Protobuf Tutorial (1)

This tutorial shows you how to get a more complex project going. What we want to accomplish is to get the addressbook example from http://code.google.com/apis/protocolbuffers/docs/cpptutorial.html going. We start at the desired output and let rake and cxx-project tell us what we have to do:) lets see how this works:

Step 1

Goals

In this step we create a directory-structure with: * the sources from the protobuf webpage * minimal rakefile to get going * a cxxproject-file to get the two executables addressbook_(read|write)

Code

mkdir -p protobuf_cxx_example/addressbook
cd protobuf_cxx_example
create addressbook/addressbook_read.cc, addressbook/addressbook_write.cc and addressbook/addressbook.proto from the webpage
please adjust the includes in the *.cc files to #include "addressbook/addressbook.pb.h"

create addressbook/project.rb with:
cxx_configuration do

  exe 'addressbook_write',
    :sources => ['addressbook_write.cc'],
    :dependencies => ['addressbook_pb_api']

  exe 'addressbook_read',
    :sources => ['addressbook_read.cc'],
    :dependencies => ['addressbook_pb_api']

end
create Rakefile.rb with:
require 'cxxproject'
cxx(FileList['**/project.rb'], "build", "gcc", './') do

Explanation

in the cxx-projectfile we say, that we want to build 2 executables by giving a sourcefile and depending on the addressbookpbapi (which will be a library created from the generated sources). the rakefile simply collects all *project.rb files in all directories, gives build as outputdirectory for the compilation process, chooses gcc as toolchain and . as working directory.

Next Steps

rake
ERROR: while reading config file for addressbook_write: dependent building block "addressbook_pb_api" was specified but not found!

This tells us, that we have to tell cxxproject how to get addressbookpbapi.

Step 2

Goals

No we have to tell cxxproject how it can build the building block addressbookpbapi.

Code

add to addressbook/project.rb:
source_lib'addressbook_pb_api',
  :sources => ['../build/protoc/addressbook/addressbook.pb.cc'],
  :includes => ['../build/protoc'],
  :dependencies => ['protobuf']

Explanation

This tells cxxproject that the library addressbookpbapi can be build from the source gen/addressbook/addressbook.pb.cc and that this library depends on the protobuf library

Next Steps

rake
ERROR: while reading config file for addressbook_pb_api: dependent building block "protobuf" was specified but not found!

This tells us that cxxproject does not know about a buildingblock for protobuf.

Step 3

Goals

We want to have a cxx-project buildingblock for the protobuf-library. To start simple this tutorial assumes, that you have installed the protobuf-dev libs (for ubuntu this means, that you should install protobuf-compiler and libprotobuf-dev).

Code

create protobuf_project.rb with:
cxx_configuration do
  BinaryLibrary.new('protobuf')
end

Explanation

This tells cxxproject that there is a binary library (located in the default paths) for protobuf.

Next Steps

rake exe:filter
Error build/build/protoc/addressbook/addressbook.pb.cc.o: Don't know how to build task 'build/protoc/addressbook/addressbook.pb.cc'

When we now try to build all executables rake tells us, that it does not know how to build addressbook/gen/addressbook/addressbook.pb.cc.

Step 4

Goals

We have to kick off the protoc compiler. As cxxproject is not aware of pro tobuf we have to define normal raketasks to get this goal.

Code

add to Rakefile.rb:
PROTOC = '/usr/bin/protoc'
GEN_FOLDER = File.join('build', 'protoc')

directory GEN_FOLDER

desc 'protoc addressbook.proto'
file File.join(GEN_FOLDER, 'addressbook', 'addressbook.pb.cc') => [File.join('addressbook', 'addressbook.proto'), GEN_FOLDER, PROTOC] do
  command = "#{PROTOC} --cpp_out=#{GEN_FOLDER} #{File.join('addressbook', 'addressbook.proto')}"
  sh command
end

Explanation

This tells rake how to create the needed files with protoc.

Next Steps

rake exe:filter

This seems to work just fine ... lets try it out!

build/addressbook_write.exe test

Great!

Wrap Up

This short tutorial showed you how to setup the addressbook example from protobuf. In 4 simple steps it builds two executables, using the preinstalled protobuf library on your system. Make sure to check the accompanying git-repository@https://github.com/gizmomogwai/cxxprojecttutorials (branch protobuftutorial_1).