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I need to debug some pure functions in a fortran Program compiled with gfortran. Is there any way to ignore the pure statements so I can use write, print, etc. in these pure functions without great effort? Unfortunately it is not easly possible to just remove the pure statement.

Wauzl
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2 Answers2

8

You can use a macro and use the -cpp flag.

#define pure 

pure subroutine s
 print *,"hello"
end
Vladimir F Героям слава
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  • I just added the flags `-cpp` and `-Dpure=` to my compiling command. Really great idea! – Wauzl Sep 26 '13 at 20:28
  • For `elemental` routines in Fortran 2008, you can use `-Delemental="IMPURE ELEMENTAL"`. The capital letters are use to avoid recursive macro substitution. It works since Fortran is case insensitive. – Antoine Lemoine Aug 30 '21 at 15:36
4

I usually use the pre-processor for this task:

#ifdef DEBUG
subroutine test(...)
#else
pure subroutine(...)
#endif
  ! ...
#ifdef DEBUG
  write(*,*) 'Debug output'
#endif
  ! ...
end subroutine

Then you can compile your code with gfortran -DDEBUG for verbose output. (In fact I personally do not set this flag globally, but via #define DEBUG at the beginning of the file I want debug).

I also have a MACRO defined to ease the use of debugging write statements: 

#ifdef DEBUG
#define dwrite write
#else
#define dwrite ! write
#endif

With this, the code above reduces to: 

#ifdef DEBUG
subroutine test(...)
#else
pure subroutine(...)
#endif
  ! ...
  dwrite (*,*) 'Debug output'
  ! ...
end subroutine

You can enable the pre-processor with -cpp for gfortran, and -fpp for ifort. Of course, when using .F90 or .F, the pre-processor is enabled by default.

Alexander Vogt
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