GNU-C-preprocessing FORTRAN source to change array indices causes recursion whilst expanding macro

Question

I am parallelizing an existing FORTRAN application. I don't want to directly change parts of its code so I am using preprocessor directives to accomplish my goal. This way I am able to maintain the readability of the code and I won't induce errors in parts of the code that have already been tested. However, when I try to preprocess my source with the GNU C preprocessor I get the following error message (gcc version 4.7.2 (Debian 4.7.2-5)):

test.f:9:0: error: detected recursion whilst expanding macro "ARR"" 

This simple test program demonstrates my problem:

      PROGRAM TEST

        IMPLICIT NONE
        INTEGER I,OFFSET,ARR(10)

#define ARR(I) ARR(OFFSET+I)

        DO I=1,10
          ARR(I)=I
        END DO

#undef ARR(I)

      END PROGRAM TEST

This is the commandline output:

    testing$ gfortran -cpp -E test.f
# 1 "test.f"
# 1 "<command-line>"
# 1 "test.f"
      PROGRAM TEST

[...]

test.f:9:0: error: detected recursion whilst expanding macro "ARR"
        DO I=1,10
          ARR(OFFSET+OFFSET+OFFSET+OFFSET+OFFSET+OFFSET+OFFSET+OFFSET+OFFSET+OFFSET+OFFSET+OFFSET+OFFSET+OFFSET+OFFSET+OFFSET+OFFSET+OFFSET+OFFSET+OFFSET+OFFSET+I)=I
        END DO

[...]

      END PROGRAM TEST

This site provides some information on the preprocessor I am using:

http://tigcc.ticalc.org/doc/cpp.html#SEC10

As it seems I am using a function-like macro with macro arguments.

Why is the preprocessor detecting a recursion? [EDIT] - Maybe because I use the same name for Makro and Identifier?
Why isn't the preprocessor capable of interpreting upper case directives (#DEFINE instead of #define)? - I am asking, because I haven't had this problem with the ifort preprocessor.

BTW: I am able to preprocess the original code either using the ifort preprocessor -fpp, or by changing the source in the following way:

      PROGRAM TEST

        IMPLICIT NONE
        INTEGER I,OFFSET,ARR(10)

#define ARR_T(I) ARR(OFFSET+I)

        DO I=1,10
          ARR_T(I)=I
        END DO

#undef ARR_T(I)

      END PROGRAM TEST

Answer 1

Why is the preprocessor detecting a recursion? [EDIT] - Maybe because I use the same name for Makro and Identifier?

The preprocessor is detecting recursion because your macro name and array name are the same.

Why isn't the preprocessor capable of interpreting upper case directives (#DEFINE instead of #define)? - I am asking, because I haven't had this problem with the ifort preprocessor.

When using gfortran, you are using a C preprocessor. #DEFINE is not a recognized preprocessor directive in C. No idea about ifort. I thought in ifort you had to prefix macros with !$MS or !$DEC.

Your change to the program to get it to work for ifort will also work for gfortran.