Passing Long Integers Between QuickBASIC and MPW Pascal 3.00 (57347)

MORE INFORMATION

When doing interlanguage calling with Microsoft QuickBASIC, the other language can make calls to the BASIC run time to get the address of passed arguments. This is accomplished with the GetNextLibArg statement.

GetNextLibArg returns a pointer to a variant record containing another pointer to each possible type of QuickBASIC variable (single precision, double precision, integer, etc.). Usually, a double indirection of pointers is used to get the actual passed data.

Using double indirection of pointers with Apple MPW Pascal, however, does not return the correct value. This is a QuickBASIC header file problem. The routine below demonstrates how an inline assembly-language routine can be used in place of the double indirection to work around the problem.

More information on interlanguage calling with Microsoft QuickBASIC can be found in the "Microsoft QuickBASIC for Apple Macintosh: Language Reference," starting on page 444.

Compile and link PrintLng.p from Apple MPW Pascal version 3.00 as follows:

   pascal -p PrintLng.p
   link -p -rt MBPC=999 PrintLng.p.o BasicLib.a.o -o PrintLng
				

Note: The file BasicLib.a.o comes with Microsoft QuickBASIC for Apple Macintosh systems, on the Examples disk, in the User Libraries:MBPC Rsrcs:MPWP PCR Folder.

Once PrintLng is compiled and linked, use ResEdit to change parameters in PrintLng as follows:

1. In ResEdit find the newly created file PrintLng, and click once on the name so that it is highlighted.
2. While holding down the COMMAND key, press the "I" key. This is the same as choosing Get Info from the File menu. Change the following in the dialog box that appears:
   
   
   1. Change the File field to "PrintLng".
   2. Change the Type field to "MBPC".
   3. Change the Creator field to "MSBB".
3. Close the dialog box, and click Yes when asked if you want to save.
4. Double-click on PrintLng to open it. There should be one resource of MBPC displayed; double-click on this also. Single-click the displayed MBPC and press COMMAND+I. In the Get Info dialog box that is brought up, change the Name field to PrintLng.

PrintLng is now a pure code resource that can be used with the RetLng QuickBASIC program.

Code Example

The following QuickBASIC program is RetLng, which invokes an Apple MPW Pascal routine to return a series of long integer numbers:

   LIBRARY "PrintLng"

   A& = 0 : B& = 0
   CALL PrintDouble(A&, B&)
   PRINT A&; B&

   WHILE INKEY$ = "" : WEND
				

The following Apple MPW Pascal routine is PrintLng.p, which accepts a series of passed long integer numbers from a Microsoft QuickBASIC program and returns a constant value in them:

{**************************************************************}
{* PrintLng.p (c) 1989 Microsoft Corporation                  *}
{**************************************************************}
{* Description: Example to show how to pass long integer      *}
{*              number from QuickBASIC to MPW Pascal and back.*}
{**************************************************************}
{$R-}   { Turn off range checking}
UNIT PrintVerRec;

{*======================== INCLUDE FILES======================*}
USES
   {$U MemTypes.p }      MemTypes,
   {$U BasicLibMPWP.p }  BasicLib;

   procedure AssignLng (ptr: LIBARGPTR; val: LongInt);
   inline
      $225f,  { movea.l (a7)+,a1                             }
      $2e19,  { move.l  (a1)+,d7   ;get Long value           }
      $205f,  { movea.l (a7)+,a0   ;get ptr to Int variable  }
      $20C7;  { move.l   d7, (a0)+ ;assign the Int value     }

PROCEDURE Main;

{$S Main}
{*------------------------------------------------------------*
 * A routine to pass back to BASIC long integer constants     *
 *    Called from BASIC as:                                   *
 *    CALL PrintLng (< long integer argument list >)          *
 *------------------------------------------------------------*}
PROCEDURE MAIN;
VAR
   tempflag,argtype: INT16;
   valptr:  LIBARGPTR;
   templng: LongInt;

BEGIN
   argtype := GetNextLibArg(valptr,tempflag);

   WHILE (argtype <> _ARGSEND) DO
      BEGIN
         if (argtype = _LONGARG) THEN
            BEGIN
               templng := 4321;
               AssignLng(valptr, BigRec(templng));
            END;
         argtype := GetNextLibArg(valptr,tempflag);
      END;

END; {* of MAIN *}
				

Running RetLng produces the following output:

   4321  4321