Microsoft KB Archive/49399

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Example Allocating Memory in MASM Released by Basic's SETMEM

Article ID: 49399

Article Last Modified on 8/16/2005



APPLIES TO

  • Microsoft QuickBasic 4.0
  • Microsoft QuickBASIC 4.0b
  • Microsoft QuickBasic 4.5 for MS-DOS
  • Microsoft BASIC Compiler 6.0
  • Microsoft BASIC Compiler 6.0b
  • Microsoft BASIC Professional Development System 7.0
  • Microsoft BASIC Professional Development System 7.1



This article was previously published under Q49399

SUMMARY

The two programs shown below demonstrate how a Basic program can use SETMEM to free memory for an assembly routine to get dynamic memory.

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.

MORE INFORMATION

For more information about interlanguage calling between Basic and MASM, search in the Microsoft Knowledge Base using the following word:

BAS2MASM


Code Example

The following Basic program is BMEMSET.BAS, which uses SETMEM to free a block of memory for an assembly routine that uses a DOS interrupt to get dynamic memory:

   DECLARE SUB AMem(BYVAL AllocSize AS INTEGER)
   CLS
   ' Decrease the size of the far heap so AMem can use a DOS
   ' interrupt to get dynamic memory
   BeforeCall% = SETMEM(-2048)
   CALL AMem(1024%)
   ' Return the memory to the far heap; use a larger value so
   ' all space goes back into the heap.
   AfterCall% = SETMEM(3500)
   LOCATE 2, 1
   IF AfterCall% <= BeforeCall% THEN
      PRINT "Memory not reallocated"
   ELSE
      PRINT "Memory was successfully reallocated"
   END IF
   END
                

The following program is AMEMSET.ASM, which allocates and deallocates a block of memory freed by Basic:

; The following handy .MODEL MEDIUM,Basic directive is found in
; MASM 5.10 but not in earlier versions:
.MODEL MEDIUM, Basic
.DATA
        Fail    DB 'Failed to allocate memory$'
        Success DB 'Successfully allocated memory$'
.CODE
        PUBLIC AMem
AMem    PROC
        push bp
        mov bp, sp                ; set stack frame
        push cx
        push es

        mov ax, [bp+6]            ; get number of bytes freed
        mov cl, 4                 ; divide by 16 to get number of
        shr ax, cl                ;  paragraphs of memory
        mov bx, ax
        mov ah, 48h               ; DOS interrupt to allocate block
        int 21h                   ;  of memory
        mov es, ax
        mov ah, 9
        jnc NoFail                ; carry flag clear if successful
        mov dx, OFFSET Fail       ; display failed message
        int 21h
        jmp Exit                  ; go back to Basic

NoFail: mov dx, OFFSET Success    ; display success message
        int 21h
        mov ah, 49h
        int 21h

Exit:   pop es
        pop cx
        pop bp
        ret 2
AMem    ENDP
        END
                

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

   BC BMEMSET.BAS;
   MASM AMEMSET.ASM;
   LINK BMEMSET AMEMSET;
                

BMEMSET.EXE produces the following output:

Successfully allocated memory
Memory was successfully reallocated


Additional query words: QuickBas BasicCom

Keywords: KB49399