why there are lines like '#.....' in preprosssed file

[Andy]

Hi,

Sorry for spamming this naive question. I found that when I use -E
option to preprocess the file, the command as follows,
    g++ -E  myfile.cc  > myfile.cc.i

In the generated preprocessed file, there are lines start with '#'. For
example,

#343
"/usr/lib/gcc/i386-redhat-linux/3.4.2/../../../../include/c++/3.4.2/bits/locale_classes.h"
3

Can anyone give out some hints?

Thanks a lot!

Andy