clang_complete dosen't give suggestions

Question

I was trying to set up plugin clang_complete for vim. I have cloned repository from its page on github to directory ~/.vim. Then I typed there make install and I had got :

vim clang_complete.vmb -c 'so %' -c 'q'

I have set path to libclang and other required variables in my .vimrc:

:set nu
syntax on
:set paste 
let g:clang_user_options='|| exit 0'
let g:clang_complete_auto = 1
let g:clang_complete_copen = 1
let g:clang_library_path='/usr/lib/x86_64-linux-gnu/libclang3.8.so.1'
filetype plugin indent on 

Input of vim --version included -python +python3. Still vim doesn't complete expressions like:

 #include<String>
 using namespace std;
 int main()
 {
       String s;
       s.      
       return 0;
}

What could be wrong?