Using google protobuf with Qt Creator

[blah900]

Hi I am relatively new at this but I wanted to use Google's protobufs for my project.

I am using Win7.

So I used cygwin and did
./configure --enable-static --disable-shared - to create static lbirary.
make - to make
make check - all tests passed
make install - no errors that I could see

So once that happened I generated the pb file, which went fine without any problems using
protoc.exe --cpp_out=. myproto.proto

So after that I went and started a new Qt Widget project.
I added existing files myproto.pb.cc and myproto.pb.h along with the config.h that was generated when I ran configure.

This is what I have in my pro file. Qmake works fine with no error appearing.
@#-------------------------------------------------

Project created by QtCreator 2014-01-04T16:16:27

#-------------------------------------------------

QT += core gui

greaterThan(QT_MAJOR_VERSION, 4): QT += widgets

TARGET = TestProto
TEMPLATE = app

SOURCES += main.cpp
MainWindow.cpp
Map/Tile.cpp
Protobufs/myproto.pb.cc
Map/TileTest.cpp

HEADERS += MainWindow.h
Map/Tile.h
Protobufs/myproto.pb.h
Map/TileTest.h
config.h

FORMS += MainWindow.ui

LIBS += -LC:/cygwin64/usr/local/lib -lprotobuf

INCLUDEPATH += C:/cygwin64/usr/local/include
@

However when I try to build it has the following error messages (put only 4 out of 200+):
@error: undefined reference to google::protobuf::DescriptorPool::generated_pool()' error: undefined reference to google::protobuf::DescriptorPool::FindFileByName(std::string const&) const'
error: undefined reference to google::protobuf::DescriptorPool::FindFileByName(std::string const&) const' error: undefined reference to google::protobuf::internal::LogMessage::LogMessage(google::protobuf::LogLevel, char const*, int)'@

Any idea on what I am doing wrong?

I have searched for the answer but other people seem to be able to compile their code fine when they do it like this.

[SGaist]

Hi,

Just a wild guess, are you using compatible compilers for all builds ?

[blah900]

Wow, that worked!

Once things have been compiled into an .exe, I don't need to carry around the protobuf library since it's static library right?

[SGaist]

That's correct yes

[VimHar]

@blah900 hey. What have you done that made things work. I have installed protobuf using vcpkg and pointing to the static library same as you did in windows.

Except lptotobuf im using llibprotouf. Still facing the undefined erro.

[jsulm]

@VimHar said in Using google protobuf with Qt Creator:

Except lptotobuf im using llibprotouf

How do you link libprotobuf?

[VimHar]

@jsulm

LIBS += -LC:/vcpkg/installed/x64-windows/lib/ -llibprotobuf

like this

[jsulm]

@VimHar said in Using google protobuf with Qt Creator:

-llibprotobuf

-lprotobuf

[VimHar]

@jsulm Have done that. It says
:-1: error: cannot find -lprotobuf

My files in lib folder are libprotobuf.lib , libprotobuf-lite.lib , libprotoc.lib

[jsulm]

@VimHar On windows you need libprotobuf.lib to link at build time - do you have it?

[VimHar]

@jsulm Yes as stated I have these files in lib folder of the path specified,
libprotobuf.lib , libprotobuf-lite.lib , libprotoc.lib

My .pro file

QT += core gui

greaterThan(QT_MAJOR_VERSION, 4): QT += widgets

CONFIG += c++17

INCLUDEPATH += C:\vcpkg\installed\x64-windows\include\

LIBS += -LC:/vcpkg/installed/x64-windows/lib/ -lprotobuf

SOURCES +=
main.cpp
mainwindow.cpp
m.pb.cc

HEADERS +=
mainwindow.h
m.pb.h

FORMS +=
mainwindow.ui

[jsulm]

@VimHar said in Using google protobuf with Qt Creator:

-lprotobuf

Try

-llibprotobuf.lib

[VimHar]

@jsulm No same error. Cannot find llibprotouf.lib

[JonB]

@VimHar
There have been inconsistencies in the spellings of what you have typed in your various posts. Why don't you try:

LIBS += C:\vcpkg\installed\x64-windows\lib\libprotobuf.lib

Please use copy & paste of above line. If you get error please copy & paste exact text back here.

[VimHar]

@JonB said in Using google protobuf with Qt Creator:

LIBS += C:\vcpkg\installed\x64-windows\lib\libprotobuf.lib

QT += core gui

greaterThan(QT_MAJOR_VERSION, 4): QT += widgets

CONFIG += c++17

INCLUDEPATH += C:\vcpkg\installed\x64-windows\include\

LIBS += C:\vcpkg\installed\x64-windows\lib\libprotobuf.lib

SOURCES +=
main.cpp
mainwindow.cpp
m.pb.cc

HEADERS +=
mainwindow.h
m.pb.h

FORMS +=
mainwindow.ui

Sorry for the same. Even then Im getting the same undefined error faced by the actual questioner.
i.e "undefined reference to `google::protobuf::internal::AssignDescriptors(google::protobuf::internal::DescriptorTable const*, bool)''

[jsulm]

@VimHar Was the Protobuf lib built using same compiler? What compiler do you use to build your app?

[JonB]

@VimHar said in Using google protobuf with Qt Creator:

Even then Im getting the same undefined error faced by the actual questioner.
i.e "undefined reference to `google::protobuf::internal::AssignDescriptors(google::protobuf::internal::DescriptorTable const*, bool)''

Now I do not understand, because this is not the same error at all as you said you were having. You said you got one of:

. :-1: error: cannot find -lprotobuf
Cannot find llibprotouf.lib

These errors mean it could not find the library file to link with --- which is why I wanted to get you to type in the full path --- where the error now is that the library file is found, but you have an unresolved reference. Quite different kinds of error.

I think/suspect the lib file is being found but is the wrong version or built with the wrong compiler or something like that.... Please start by answering @jsulm's question with your best information.

[VimHar]

hey Thanks..JonB.. The actual intention of mine is the "undefined error" only.
Regarding compilers, I used vcpkg for installing protobuf and Qt uses MinGw64.

Is this the problem??

[jsulm]

@VimHar said in Using google protobuf with Qt Creator:

Is this the problem??

Probably.
There should be a linker warning in the build log.

[JonB]

@VimHar said in Using google protobuf with Qt Creator:

I used vcpkg for installing protobuf and Qt uses MinGw64.

I don't know what "vcpkg" is (MSVC??) but it sounds like a different compiler/linker. MinGW library files end in .a not .lib, maybe that is the cause of the "cannot find library" messages? In any case you need to use the smae compiler/linker for everything.