YouCompleteMe worked fine until I upgrade Ubuntu from 16 to 18.
Now it doesn't understand
using std::cin; saying
no member named 'cin' in namespace 'std'; did you mean 'min'?
It also doesn't read in class names defined in my own header files.
I have tried reinstalling YouCompleteMe,
git pull the latest version,
git submodule update.
I also verified/updated the path to libclang to
/usr/lib/llvm-8/lib/libclang.so in .vimrc and the path to C++ standard library to
/usr/include/c++/7/ in .vim/.ycm_extra_conf.py
All the C++ source code compiles without error with nearly identical compilation flags.