Folding doesn't work for C/C++

Question

I've been having a ridiculously hard time getting C/C++ code folding to work with set foldmethod=syntax. To debug my issue I've stripped down my vimrc to only this:

set foldmethod=syntax
syntax on                " also tried putting this first

Now when I open a cpp file, nothing is folded.

Then, doing :syntax off followed by :syntax on will fold the cpp file.

Any idea why that does something not already done by the trivial vimrc?

Answer 1

After some detective work I tracked down the cause of my issue being that I had a .vim file in my plugin directory that redefined OperatorChars, which broke the syntax based folding for C and C++.