Similar to this question for java: What happens if you edit a file during compilation?, I want to ask what would be the impact of modifying a file during C++ program compilation.

The program is using GCC for compilation. The helping tools for program building is cmake and ninja.

I always get an urge to change something in a file and then I remind myself the program is already building, so wanted to clarify it.

So, in conclusion,

1. Whether there is going to be an impact or not?
2. Some lights on underlying things happening behind the scenes during compilation?