Q49384: Example of Passing BASIC String Descriptor to MASM (Near)

Article: Q49384
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 a Microsoft BASIC program
passes a BASIC string descriptor to assembly language 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 or the Microsoft
Knowledge Base for the following word:

   BAS2MASM

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

The following BASIC program is BSTRN.BAS, which passes a string
descriptor to assembly language by near reference:

   DECLARE SUB RString(A AS STRING)
   A$ = "This is the String" + "$"  ' "$" terminates the string
                                    '     for INT call
   CALL RString(A$)
   END

The following program is ASTRN.ASM, which gets a string descriptor
from BASIC by near reference and prints the string out:

; The following handy .MODEL MEDIUM,BASIC directive is found in MASM
; 5.10 but not in earlier versions:
.MODEL MEDIUM, BASIC
.CODE
        PUBLIC RString
RString PROC
        push bp
        mov bp, sp
        mov bx, [bp+6]     ; get offset of string descriptor
        mov dx, [bx+2]     ; get address of string
        mov ah, 9          ; int call to print string
        int 21h
        pop bp

        ret 2
RString ENDP

        END

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

   BC BSTRN.BAS;
   MASM ASTRN.ASM;
   LINK BSTRN ASTRN;

BSTRN.EXE produces the following output:

   This is the string

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