Q49396: Example of Passing Variable-Length String from BASIC to MASM

Article: Q49396
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 variable-length string 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 for the following
word:

   BAS2MASM

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

The following BASIC program is BSTR.BAS, which passes the offset of a
variable-length string to assembly language:

   DECLARE SUB RString(BYVAL soff AS INTEGER)
   A$ = "This is the string" + "$"  ' "$" terminates string for INT call
   CALL RString(SADD(A$))
   END

The following program is ASTR.ASM, which gets the address of a
variable-length string and prints the string out:

.MODEL MEDIUM
.CODE
        PUBLIC RString
RString PROC
        push bp
        mov bp, sp           ; set stack frame
        mov dx, [bp+6]       ; get offset to string
        mov ah, 9            ; DOS interrupt 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 BSTR.BAS;
   MASM ASTR.ASM;
   LINK BSTR ASTR;

BSTR.EXE produces the following output:

   This is the string