TLDR:
The thrid party lib (torch) was built using a Pre-cxx11 ABI, and libs built with that couldn’t obviously be linked to the object that was using cxx11 ABI!
Long Explanation:
After hours of debugging of a code that worked just fine in windows both in Visual Studio and CMake while being a pain in the neck in linux I found the culprit!
The libtorch is shipped with two types of build Pre-cxx11 and cxx11 ABIs!
It was using the Pre-cxx11 built libs that was shipped with its Python package (torch1.6cpu) and since Anaconda3 was in the Path and I was also using it to build the libs I faced this issue.
What gave it away after all these hours was the weird arguments to the undefined methods which were : std::__cxx11::basic_string where it should have been simply std::string. I didnt expect this two to be different and thought thats a weird naming scheme the g++ is using until moments ago that made me say, lets give that a search maybe I can get something out it! lo and behold! this was the case :
If you get linker errors about undefined references to symbols that
involve types in the std::__cxx11 namespace or the tag [abi:cxx11]
then it probably indicates that you are trying to link together object
files that were compiled with different values for the
_GLIBCXX_USE_CXX11_ABI macro. This commonly happens when linking to a third-party library that was compiled with an older version of GCC. If
the third-party library cannot be rebuilt with the new ABI then you
will need to recompile your code with the old ABI.
ref
To fix this I simply directly used the libtorch cxx11 in all libs creation and that just did it. meaning, unlike what is being shown in the Pytorch’s official documentaion,
DO NOT DO:
cmake -DCMAKE_PREFIX_PATH="$(python -c 'import torch.utils; print(torch.utils.cmake_prefix_path)')" ..
By doing this all hell will break loose if you, like me expected the libs to have been built with cxx11! becasue they have not!
Note that this is not the case under windows! so if you are on linux, just grab and use the prebuilt libs with CXX11 ABI! and avoid what ships with Pytorch!