Q49397: Example of Passing a String Descriptor from MASM to BASIC

Article: Q49397
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: 13-AUG-1990

The two programs shown below demonstrate how Microsoft assembly
language can create a BASIC string descriptor and pass it to BASIC.

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 BSTRDESC.BAS, which is passed a string
created in assembly language and prints the string out:

   DECLARE SUB MkString
   CALL MkString
   END
   SUB BasicSub(TheString AS STRING)
      PRINT LEN(TheString)
      PRINT TheString
   END SUB

The following program is ASTRDESC.ASM, which builds a string
descriptor that is passed back to the calling BASIC program:

.MODEL MEDIUM
        SType   STRUC
                SLength DW 18
                Soff    DW ?
        SType   ENDS
.DATA
        StringDesc  SType <>
        TheString   DB 'This is the string'

.CODE
            EXTRN BasicSub:PROC

            PUBLIC MkString
MkString    PROC
            mov ax, OFFSET TheString       ; set up string descriptor
            mov bx, OFFSET StringDesc.Soff
            mov [bx], ax
            mov ax, OFFSET StringDesc.SLength
            push ax           ; pass address of descriptor to BASIC
            CALL BasicSub
            ret
MkString    ENDP
            END

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

   BC BSTRDESC.BAS;
   MASM ASTRDESC.ASM;
   LINK BSTRDESC ASTRDESC;

BSTRDESC.EXE produces the following output:

   This is the string