c preprocessor output: first four lines

[Roman B.]

Hi,

$  cpp file.c

alway outputs

# 1 "file.c"
# 1 "<built-in>"
# 1 "<command-line>"
# 1 "file.c"

Where as words are self-explanatory I cannot understand the meaning in
the whole. I could not find any explanation in the documentation also.

So what do those 4 lines actually mean?

Thanks

Roman