scope - Mechanics Fortran Preprocessor -

i happened come across preprocessing option fortran compilers support these days (as explained e.g. in fortran wiki) . coming c background, better understand mechanics , caveats related (fortran-)preprocessor's #include directive.

to avoid confusion right beginning: there 2 include directives in fortran (see e.g. f77 reference)

• include "foo" compiler directive, i.e. foo can contain fortran statements
• #include "bar" preprocessor directive, i.e. bar can contain #defines , like

i aware of difference , interested in second case (my question therefore not duplicate of this post).

i'll explain questions using example: assume have 2 files, header file (macro.h) , source file (display.f):

macro.h

#define msg() say_hello() 

display.f

#include "macro.h"      program display     call msg()     call another_message()     end      subroutine say_hello()     write(*,*) 'hello.'     end      subroutine another_message()     call msg()     end 

here questions:

scope

where (globally, locally in subroutine etc.) macro msg() defined if include macro.h:

1. at beginning of file (as above)?
2. at beginning of program display (and else)?
3. at beginning of e.g. subroutine another_message() (and else)?

from testing seems: 1. globally, 2. in program , subroutines, 3. in subroutine only. confirmation of these assumptions , theoretical explanations why great.

what of above (1. - 3.) best practice preprocessor includes?

include guards

if have multi-file project , include header.h in multiple *.f source files, need provide include guards?

in case answers above questions should compiler dependent (as preprocessing not fortran standard), i'd interested in ifort's behaviour.

the rules same c preprocessor know. gcc uses same cpp c , fortran (for fortran in traditional mode). therefore there no scope around, text , preprocessor doesn't care program units.

therefore, 1., 2. , 3. valid place of definition until file end or until #undef. valid in recursively #included files.

if guards mean #undef yes, otherwise warning or error redefinition appears, if include files single file. if independent no.

the key think preprocessor text replacement tool. knows nothing fortran.

last thing, preprocessor non-standard, available.