PRB: L2029 '_exit' Unresolved External from STOP Stmt in DLL

• Microsoft FORTRAN for MS-DOS, version 5.1

SYMPTOMS

An attempt to link a dynamic-link library (DLL) for the Microsoft Windows operating system fails and Microsoft LINK generates the following message:

   error L2029: '_exit' : unresolved external

CAUSE

Microsoft FORTRAN does not support using the STOP statement in a DLL developed for Windows.

RESOLUTION

To terminate the DLL and the calling application, use the SendMessage() function in the Windows application programming interface (API) to send the calling application a WM_QUIT message. The code example below demonstrates this technique.

MORE INFORMATION

The code example below terminates the DLL and the calling application after displaying a message box warning the user to save all data.

Sample Code - EXIT.FOR

C Compiler options needed: /c /Od /Zi /AL

      interface to integer*2 function PostAppMessage[pascal]
     + (htask, msg, wparam, lparam)
      integer*2 htask[value]
      integer*2 msg[value]
      integer*2 wparam[value]
      integer*4 lparam[value]
      end

      interface to integer*2 function GetCurrentTask[pascal]
      end

      interface to integer*2 function MessageBox[pascal]
     + (hwnd, boxtext, caption, boxtype)
      integer*2   hwnd[value]
      character*1 boxtext[reference]
      character*1 caption[reference]
      integer*2   boxtype[value]
      end

      subroutine exit
      integer*2 in
      character buffer1*120, buffer2*80
      integer*2 i, WM_QUIT, PostAppMessage, GetCurrentTask, MessageBox
      WM_QUIT = #12

      buffer1 =
     +'************** DLL issued STOP Statement ************'//
     +'\n  Application will terminate. Save contents of windows NOW'c
      buffer2 = 'DLL STOP'c

      i = MessageBox(0, buffer1, buffer2, 0)
      i = PostAppMessage(GetCurrentTask(), WM_QUIT, in, 0)
      return
      end

Sample Code - TEST.FOR

C Compiler options needed: /c /Od /Zi /MW

      program testdllstop
      print *, 'before calling DLL'
      call dllsub
      print *, 'back from sub1'
      end

Sample Code - DLLTEST.FOR

C Compiler options needed: /c /Od /Zi /Aw /Gw

      interface to integer*2 function MessageBox[pascal]
     + (hwnd, boxtext, caption, boxtype)
      integer*2   hwnd[value]
      character*1 boxtext[reference]
      character*1 caption[reference]
      integer*2   boxtype[value]
      end

      subroutine dllsub
      integer*2 messagebox
      i = MessageBox(int2(0), 'Prior to STOP statement in DLL'c,
     + ' 'c, 0)
      call exit
      end

DLLTEST.DEF

LIBRARY     DLLTEST
EXETYPE     WINDOWS
CODE        PRELOAD MOVEABLE DISCARDABLE
DATA        PRELOAD MOVEABLE SINGLE
HEAPSIZE    1024
EXPORTS     DLLSUB
            WEP

MAKEFILE

all: test.exe dlltest.dll

test.obj: test.for

   fl /c /Od /Zi /MW test.for

   fl /c /Od /Zi /Aw /Gw dlltest.for

   fl /c /Od /Zi /AL exit.for

   link dlltest exit, dlltest.dll, nul, /co /nod ldllfew, dlltest.def;

   implib dlltest.lib dlltest.def

   link test, test, nul, /co /nod llibfew dlltest,
      c:\fortran\binb\fl.def;