Preprocessor

[Ian Rutt]

Hi,

I've been trying to use gfortran with code containing preprocessor
lines. For this sample code:

-------------------------------------------------------------------

program test_pp

#ifdef SINGLE
  integer,parameter :: rk=4
#else
  integer,parameter :: rk=8
#endif

end program test_pp

-------------------------------------------------------------------

I get this output:

-------------------------------------------------------------------

Warning: test_dp.f90:4: Illegal preprocessor directive
Warning: test_dp.f90:6: Illegal preprocessor directive
Warning: test_dp.f90:8: Illegal preprocessor directive
 In file test_dp.f90:7

  integer,parameter :: rk=8
                        1
Error: Symbol 'rk' at (1) already has basic type of INTEGER

-------------------------------------------------------------------

If I compile with -E (run preprocessor only), I don't get any errors.
Should this code compile or not? Have I made some sort of mistake in my
installation (e.g. environment variables)? 

I'm using GCC 4.1.0 20050415 (experimental).

I realise that preprocessor directives are not part of the f95 standard,
but most other compilers support them, and they're a very useful
extension. 

Thanks,

Ian