What is a .h.gch file?

Question

I recently had a class project where I had to make a program with G++.

I used a makefile and for some reason it occasionally left a .h.gch file behind.

So

Answer 1

a) They're precompiled headers: http://gcc.gnu.org/onlinedocs/gcc/Precompiled-Headers.html

b) They contain "cached" information from .h files and should be updated every time you change respective .h file. If it doesn't happen - you have wrong dependencies set in your project