Q149746: BUG: Access Violation Calling Exported Subroutine in DLL

Article: Q149746
Product(s): Microsoft Fortran Compiler
Version(s): 4.0
Operating System(s): 
Keyword(s): kbFortranPS kbLangFortrankbbuglist
Last Modified: 02-NOV-1999

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The information in this article applies to:

- Microsoft Fortran PowerStation for Windows 95 and Windows NT, version 4.0 
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SYMPTOMS
========

When you use the !MS$ATTRIBUTES DLLEXPORT attribute to export a DLL's
subroutine, and call that subroutine from another subroutine within the same DLL
it causes the following Access Violation:

  The instruction at "0x00000000" referenced memory at "0x00000000".
  The memory could not be "written"

RESOLUTION
==========

If you need to call an exported subroutine in a DLL, you should put this code
into a non-exported helper subroutine and have the exported subroutine call the
non-exported helper subroutine.

STATUS
======

Microsoft has confirmed this to be a bug in the Microsoft products listed at the
beginning of this article. We are researching this problem and will post new
information here in the Microsoft Knowledge Base as it becomes available.

MORE INFORMATION
================

Steps to Reproduce Problem
--------------------------

1. Build the DLL using the sub.for file listed below. At the MS-DOS command-line
  prompt, type:

  " fl32 /LD sub.for" (without the quotation marks)

2. Build the MAIN program using the main.for file listed below, and link it to
  the DLL static library file created in Step 1. At the same MS-DOS
  command-line prompt, type:

  " fl32 main.for sub.lib" (without the quotation marks)

Sample Code to Illustrate Problem
---------------------------------

MAIN
----

  ! filename: main.for
  ! Compile options needed: none
        program fortapp
          interface
            subroutine thesub()
              !ms$attributes dllimport, stdcall :: thesub
            end subroutine
          end interface
     call thesub()
        end program fortapp

DLL
---

  ! filename: sub.for
  ! Compile options needed: /LD
        subroutine thesub()
          !ms$attributes dllexport, stdcall :: thesub
            interface
              subroutine othersub()
                !ms$attributes dllexport, stdcall :: othersub
              end subroutine othersub
       end interface
          call othersub()
        end subroutine
        subroutine othersub()
          !ms$attributes dllexport, stdcall :: othersub
        end subroutine

Additional query words: 4.00

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Keywords          : kbFortranPS kbLangFortran kbbuglist
Technology        : kbAudDeveloper kbPTProdChange kbFortranSearch kbFORTRANPower400NT
Version           : :4.0

=============================================================================

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