I uninstalled vim74 and compiled vim81 and installed it. However I found it strange, comparing to vim74. When there's no .vimrc file under HOME dir, I open a c++ file and syntax highlight is working and I can use Backspace to delete letters. However when I add a .vimrc under HOME dir and just put set number into it, when the c++ source file is opened, no highlight, and Backspace not working. Why is that ? I used to add some configurations in .vimrc under vim74 before, and this situation never happens.