Passing Integers Between QuickBASIC and MPW C Version 3.00 (59533)

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 LSC or Apple MPW C, 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.

For more information on interlanguage calling with Microsoft QuickBASIC, see the "Microsoft QuickBASIC for Apple Macintosh: Language Reference" manual, starting on page 444.

Compile and link SumIntArgs.c from Apple MPW Pascal version 3.00 as follows:

   c -p SumIntArgs.c

   link -p -c MSBB -o SumIntArgs -rt MBPC=2 -t MBPC -sn MAIN=SumIntArgs
   BasicLib.a.o SumIntArgs.c.o
				

Note: The file BasicLib.a.o comes with Microsoft QuickBASIC for the Apple Macintosh on the Examples disk in the "User Libraries:MBPC Rsrcs:MPWC PCR" folder.

After compiling and linking, SumIntArgs is a pure code resource that can be used with the SumInt QuickBASIC program.

Code Example

The following QuickBASIC program is SumInt, which invokes an Apple MPW C routine to sum a series of passed integers:

   DEFINT a-z
   LIBRARY "SumIntArgs"
   a = 0     ' Initialize passed values
   b = 2
   c = 4
   d = 8
   CALL SumIntArgs(a, b, c, d)        ' CALL Pascal routine
   PRINT "Sum of: "  b;" ";c;" and ";d  ' Display returned values
   PRINT "Is: "a
   WHILE INKEY$ = "" : WEND             ' Wait for key press
				

The following Apple MPW C routine is SumIntArgs.c, which accepts a series of passed integers from a Microsoft QuickBASIC program and returns the sum of the integers:

/*************************************************************
 * IntSum.c (c) 1989 Microsoft Corporation                   *
 *************************************************************
 * Description:  Example to show how to pass integers from   *
 *               QuickBASIC to MPW C and back.               *
 *************************************************************/ 

/*========================= INCLUDE FILES ===================*/ 
#include "BasicMPWC.h"
pascal void AssignInt(LIBARGPTR ptr, INT16 val) = {
   0x3E1F,    /* move.w  (a7)+,d7  ; get int value           */ 
   0x205F,    /* movea.l (a7)+,a0  ; get ptr to Int variable */ 
   0x3087     /* move.w   d7, (a0) ; assign the Int value    */ 
};

PUBLIC VOID MAIN() {
   INT16      tempflag, argtype, NextInt, Sum;
   LIBARGPTR  valptr, pSum;

   Sum = 0;
   argtype = GetNextLibArg(&pSum, &tempflag);
   argtype = GetNextLibArg(&valptr, &tempflag);

   while (argtype != _ARGSEND) {
      if (argtype != _NULLARG)
         if (argtype == _INTARG) {
            NextInt = IntegerArg();
            Sum = Sum + NextInt;
         }
      argtype = GetNextLibArg(&valptr, &tempflag);
   }

   AssignInt(pSum, Sum);
} /* MAIN */ 
				

Running SumInt produces the following output:

   Sum of:  2   4 and 8
   Is:  14