Meaning of # in code

[chillwx@gmail_com]

I have a general question regarding the .F90 files that make up CAM3. What does the # mean ? And how is it different from the ! ?

For example, here's some code from the history.F90 file from the "Control" directory of the source code:

#if ( ! defined COUP_SOM ) && ( ! defined COUP_CSM )
use sst_data, only: sst
#endif

#include
#include
!
! Local variables
!
character*80 name ! variable name
character*80 filename ! filename to write

I believe the that "!" is just a comment symbol, similar to "c" in various versions of fortran. What about the #?

 

[olson]

You are correct that the ! and # are different. ! is a comment, while # delimits "cpp" directives which
are used to modify code just prior to compilation.