Can we compile C library as .Net dll (containing and opening access to all C libs functions) by just compiling cpp project containing code like
extern \"C\"
It really depends on your C code.
P/Invoke is often the easiest to start with, and IMO is pretty workable for a handful of functions. Performance isn't necessarily great, and I wouldn't construct an entire program out of it - but to reuse some functions, it's worthwhile.
Going from C to /clr:pure requires you to:
The current state of your code (and it's libraries) will dictate how painful that process is.