Parameter defined in DLL not exported

[psantos]

Hi to all,

In the past I have successfully exported variables defined within a DLL using the "DLL Export" directive. Despite of this, right now I'm having trouble exporting some variables with the parameter attribute. As an example consider the following code:

[fortran]module exports

    implicit none

    logical :: logical_wait=.True.                        
    !dec$ attributes dllexport :: logical_wait
    integer :: app_run_count=-1                         
    !dec$ attributes dllexport :: app_run_count

    integer, parameter ::                 max_ib2 = 40,max_jb1 = 40 !not exported
    !dec$ attributes dllexport :: max_ib2,max_jb1
    integer ::                            ib2_shared = -1,jb1_shared=-1
    !dec$ attributes dllexport :: ib2_shared,jb1_shared
    real, dimension(max_ib2,max_jb1) ::   x0_shared=1.5,y0_shared=1.5,z0_shared=1.5
    !dec$ attributes dllexport :: x0_shared,y0_shared,z0_shared

end module exports[/fortran]

Compiling and linking as a DLL and running the "dumpbin" with /exports switch reveals:

[bash]Dump of file export_problem.dll

File Type: DLL

  Section contains the following exports for export_problem.dll

    00000000 characteristics
    4D48A66E time date stamp Wed Feb 02 00:33:50 2011
        0.00 version
           1 ordinal base
           7 number of functions
           7 number of names

    ordinal hint RVA      name

          1    0 00007B08 EXPORTS_mp_APP_RUN_COUNT = _EXPORTS_mp_APP_RUN_COUNT
          2    1 00007B04 EXPORTS_mp_IB2_SHARED = _EXPORTS_mp_IB2_SHARED
          3    2 00007B00 EXPORTS_mp_JB1_SHARED = _EXPORTS_mp_JB1_SHARED
          4    3 00007B0C EXPORTS_mp_LOGICAL_WAIT = _EXPORTS_mp_LOGICAL_WAIT
          5    4 00006200 EXPORTS_mp_X0_SHARED = _EXPORTS_mp_X0_SHARED
          6    5 00004900 EXPORTS_mp_Y0_SHARED = _EXPORTS_mp_Y0_SHARED
          7    6 00003000 EXPORTS_mp_Z0_SHARED = _EXPORTS_mp_Z0_SHARED

  Summary

        5000 .data
        1000 .rdata
        1000 .reloc
        1000 .rsrc
        1000 .text
        1000 .trace[/bash]

As one can see the max_ib2 and max_jb1 are not listed and consequently they were not exported. So I ask, is it possible to export parameters? Thank you in advance.

Pedro

[Steven_L_Intel1 · Accepted solution]

There is no such thing in Fortran as "variables with the parameter attribute". A declaration that includes the PARAMETER attribute declares a "named constant", which is meaningful only during Fortran compilation. This is not something that can be DLLEXPORTed.

You can DLLEXPORT initialized variables (no PARAMETER), but this does not prevent them from being modified during execution.

[psantos]

Steve,

I agree with you. I was a wrong when I wrote "variables with the parameter attribute". Despite of this I'm out of luck exporting this constants... Thank you for your answer.
There is another way that allows exporting and at the same time protects the variable from being modified?

Pedro

[Steven_L_Intel1]

I am not aware of a way of DLLEXPORTing a value that prevents it from being modified. Let me suggest that rather than using DLLEXPORTed variables, you define a "GET" function that returns the value, which could be a PARAMETER. This will protect it from being modified.

[abhimodak]

Hi Steve and Pedro

Perhaps "Protected" may be used in this case? The test case below works. The dependency walker does show variable JJ being exported and the main program cannot modify it directly.

Abhi

-----

[fortran]      Module OM
         Implicit None
            !DEC$ ATTRIBUTES DLLEXPORT :: JJ         
         Integer, Protected :: JJ = 10
      Contains
         Subroutine Set(j)
            !DEC$ ATTRIBUTES DLLEXPORT :: Set
            Integer, Intent(IN) :: j
            JJ = j
         End Subroutine Set
         Subroutine Get(j)
            !DEC$ ATTRIBUTES DLLEXPORT :: Get
            Integer, Intent(OUT) :: j
            j = JJ
         End Subroutine Get         
      End Module OM
      
       Program Test_ProtectedFromDLL
         Use OM
         Implicit None
         Print *, JJ
       End Program Test_ProtectedFromDLL [/fortran]

[Steven_L_Intel1]

PROTECTED simply makes the Fortran compiler enforce language rules when it sees the attribute. It does not put the variable in read-only storage (because the defining module is allowed to modify it.) Once you DLLEXPORT the variable, there is no protection.

The only thing that comes to mind is quite awkward - a separate DLL that contains only the variables to be exported and a linker directive to mark the .DATA image section R (for read-only).

[psantos]

Thank you Steve and abhimodak for your suggestions.

I have already implemented a subroutine that returns my parameters and it works fine. It' s probably the best and simple solution to achieve what I want. Thank you again.

Pedro