Re: Preprocess files with gcc/gfortran vs. cpp

[LMH <lmh_users-groups at molconn dot com>]

Nick Papior wrote:
> Oh, sorry, I haven't made it clear. I do not want to mix C and fortran.
> I simply want the preprocessor capabilities in fortran as they work in C.
> I want to dynamically create a large range of modules/variable-types etc.
> This is much easier using preprocessors.
> I know one could do bash/sed/functions/awk/etc combinations to arrive
> at the same... but... :)
> 
> 2016-02-19 22:27 GMT+01:00 LMH <lmh_users-groups@molconn.com>:
>>
>>
>> Nick Papior wrote:
>>> Damnit, I was kind-of hoping this would not break compatibility. :(
>>>
>>> Then I guess I am forced to use cpp to create my actual sources.
>>>
>>> Thanks for the prompt answer!
>>>
>>> PS. Are there options to use the C-processor with gfortran?
>>> I tried:
>>> $> gfortran -Xpreprocessor "-x c11-cpp-input" <source>
>>> f951: Error: command line option â-x c11-cpp-inputâ is valid for the
>>> driver but not for Fortran
>>>
>>> hrmph...
>>>
>>> 2016-02-19 20:30 GMT+01:00 Jonathan Wakely <jwakely.gcc@gmail.com>:
>>>> On 19 February 2016 at 19:01, Nick Papior wrote:
>>>>> Am I missing some point here?
>>>>> I would have expected gcc/gfortran to use the _same_ preprocessing
>>>>> utility as that provided in cpp?
>>>>
>>>> By default cpp works in C mode, but when invoked by the Fortran
>>>> front-end it runs in a different mode. If you use cpp -x f97-cpp-input
>>>> then it works in F95 mode, and you get results consistent with
>>>> invoking gcc on a .f file, or invoking gfortran.
>>>>
>>>> I don't know why cpp treats C and Fortran input differently, but
>>>> that's why you don't see what you expect.
>>>
>>>
>>>
>>
>>> PS. Are there options to use the C-processor with gfortran?
>>
>> With g77, if you named your src file with the .FPP extension, the
>> compiler would run the code through the c pre-processor and then compile
>> as fortran. This would let you use c style includes and compiler
>> directives for code compiled as fortran. You cannot use fortran style
>> includes in the same file (like a common statement), you have to choose
>> one or the other.
>>
>> This is the make rule I used,
>>
>> INCLUDES = -I ${SOURCELOC}/src_common_depend
>> OPTIMIZE = -O2
>> FCOMP = g77-3
>> FCFLAGS = $(INCLUDES) $(OPTIMIZE) -mno-cygwin
>>
>> $(BDIR)/%.o: $(SOURCELOC)/%.FPP
>>         $(FCOMP) $(FCFLAGS) -c -o $@ $<
>>
>> the no-cygwin flag is depreciated and as I said, this example was for
>> gcc3/g77. I have done some of this with gfortran, but only for linux.
>>
>> In some ways, it can be easier to separate your cpp and fortran code and
>> just have your fortran be a function called from cpp. Let the fortran
>> have it's own variable namespace and use the fortran pre-processor. As
>> long as you can send and return what you need to and from the fotrran
>> function, everything should work fine. It's not supper efficient since
>> the fortran and c code often have their own copies of each variable, but
>> that is often not a major issue anymore.
>>
>> LMH
>>

I guess it is not entirely clear to me what you need to do, but you can
run fortran code through the c preprocessor buy using the .FPP extension
on your src files and using gfortran as your compiler. I believe that
was one of the questions asked earlier in the thread.

Something like,

FCOMP = gfortran
$(BDIR)/%.o: $(SOURCELOC)/%.FPP
    $(FCOMP) -c -o $@ $<

This would give you fotran objects that were run through the c
preprocessor to let you use c includes, c comments, macros and compiler
directives, but prohibit fortran comments and includes, parameter
statements, common statements,  etc.

I have no idea if that helps or not, but it does work.

LMH