[Bug fortran/97031] the content of a comment line breaks compilation

[jean-pierre.flament@univ-lille.fr]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97031

--- Comment #5 from jean-pierre.flament@univ-lille.fr ---
I am sorry to bother you once again, for the last time. I have now understood
all things that happened while compiling the very complicated (!) program
below. 

========================
program tstmak
   implicit none
!     a comment with /*
   integer :: i
!
#ifdef _MYDEBUG_
   print *,' debug printing'
#endif
   i = 25
   print *,'normal printing: i=',i
end program tstmak
========================================

I compiled this fortran with and without -cpp, and always with -D_MYDEBUG_ in a
command like that one

gfortran -v -ffree-form -Wall -msse2 -g -fbounds-check -fbacktrace  -D_MYDEBUG_
 -cpp tstmak1.f -o v1

1) if -cpp is PRESENT 
   a) the '/*' in the comment line causes a great problem (in that case an "end
of file") and no executable is produced 
   b) if I change the '/*' to anything else, no message, the executable is
produced, and prints what is expected
2) if -cpp is ABSENT
   a) the '/*' in the comment line has no catastrophic effect, but a WARNING
appears 
      "Warning: tstmak.f:6: Illegal preprocessor directive"
      however the executable is produced, and prints what is expected

It is because of this warning (and not an error) that I always put "-cpp" in my
makefiles !

===> conclusion:  gfortran "tolerates" and understands "#" type directives. 
     This is in opposition to other compilers, which also caused my trouble

Sorry for the  disturbance

JP Flament

----- Mail original -----
De: "kargl at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
À: "jean-pierre flament" <jean-pierre.flament@univ-lille.fr>
Envoyé: Dimanche 13 Septembre 2020 11:55:28
Objet: [Bug fortran/97031] the content of a comment line breaks compilation

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97031

--- Comment #3 from Steve Kargl <sgk at troutmask dot apl.washington.edu> ---
On Sun, Sep 13, 2020 at 08:02:01AM +0000, jean-pierre.flament@univ-lille.fr
wrote:
> 
> I just noticed that cpp recognizes the extensions .fpp .F and other uppercase
> extensions. 
> This is why I added -cpp in the gfortran command (otherwise I have a diagnostic
> because of #ifdef's
> 
> I have renamed my file with the  .fpp extension; with  "-cpp" in the gfortran
> submission I get the same errors.
> 
> If I compile the file with extension *.f or .fpp without -cpp  
> 
>  1) the compilation has no error 
>  2) a #ifdef...#endif is recognized even with a .f extension, without -cpp, in
> my simple example, (I should check that the directive really is taken into
> account !) 
>  3) IF I compile my full project in a makefile, the absence of "-cpp" in the
> gfortran command induces 
>     a "Illegal preprocessor directive" error in all the routines having that 
> #ifdef...#endif
> 

I don't quite follow you.  But, it come down to gfortran uses
the C pre-processor when asked to pre-process a file.  If you 
have a C language construct such as '/*' in your Fortran code 
it will cause problems.