Q49388: Example of Passing Fixed-Length String Between BASIC and MASM

Article: Q49388
Product(s): See article
Version(s): 4.00 4.00b 4.50
Operating System(s): MS-DOS
Keyword(s): ENDUSER | B_BasicCom H_MASM S_QuickASM | mspl13_basic
Last Modified: 10-AUG-1990

The two programs below demonstrate how Microsoft BASIC and assembly
language pass fixed-length strings by near reference.

This information about interlanguage calling applies to QuickBASIC
versions 4.00, 4.00b, and 4.50 for MS-DOS, to Microsoft BASIC Compiler
versions 6.00 and 6.00b for MS-DOS and MS OS/2, and to Microsoft BASIC
Professional Development System (PDS) versions 7.00 and 7.10 for
MS-DOS and MS OS/2.

For more information about passing other types of parameters between
BASIC and MASM, search in the Software/Data Library for the following
word:

   BAS2MASM

Code Example
------------

The following BASIC program is BFSTRN.BAS, which creates a
fixed-length string that is passed to assembly language to print and
receives a fixed-length string from assembly:

   DECLARE SUB RString(BYVAL offs AS INTEGER)
   TYPE fixstring
      s AS STRING * 20
   END TYPE
   DIM a AS STRING * 20
   CLS
   a = "BASIC String$"      ' "$" terminates string for assembly
   CALL RString(VARPTR(a))
   END
   SUB BasicSub(a AS fixstring)
      LOCATE 2, 1    ' Must LOCATE because print in assembly won't move
      PRINT a.s      '   BASIC's screen position
   END SUB

The following program is AFSTRN.ASM, which gets a fixed-length string
by near reference, prints the string, then passes a string to a BASIC
subprogram:

; The following handy .MODEL directive is found in MASM 5.10 but not
; in earlier versions:
.MODEL MEDIUM, BASIC
EXTRN BasicSub:PROC
.DATA
  astr  DB 'Assembly String      '

.CODE

        PUBLIC RString
RString PROC
        push bp
        mov bp, sp           ; set stack frame
        mov dx, [bp+6]       ; address of string
        mov ah, 9            ; DOS interrupt to print string
        int 21h

        mov ax, OFFSET astr  ; address of assembly string
        push ax              ; pass it to BASIC
        call BasicSub

        pop bp
        ret 2
RString ENDP

        END

To demonstrate these programs from an .EXE program, compile and link
as follows:

   BC BFSTRN.BAS;
   MASM AFSTRN.ASM;
   LINK BFSTRN AFSTRN;

BFSTRN.EXE produces the following output:

   BASIC String
   Assembly String