Q30887: Accessing MASM Structure Fields in a Multimodule Program

Article: Q30887
Product(s): Microsoft Macro Assembler
Version(s): 5.0,5.1,6.0
Operating System(s): 
Keyword(s): 
Last Modified: 06-MAY-2001

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The information in this article applies to:

- Microsoft Macro Assembler (MASM), versions 5.0, 5.1, 6.0 
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SUMMARY
=======

To use a structure, defined in one module with the STRUC (STRUCT in MASM 6.0)
operator, in another module with the Macro Assembler, you must take into account
the fact that the structure definition must be available to both modules at
assemble time. The structure field operator (.) can then be used to access the
structure's contents.

MORE INFORMATION
================

The following program demonstrates the use of a structure in a two-module
program:

  ; Source file 1:

  EXTRN changecow:NEAR                ; Near function call

  animals    STRUC                    ; Structure definition
      cat    db    "catfield      "
      dog    db    "dogfield      "   ; Field widths of 15 characters
      cow    db    "cowfield      "
  animals    ENDS

  .MODEL small

  .DATA
             PUBLIC zoo
  zoo        animals   <"felix","spot","Holstein">  ; Initialize fields

  .CODE
  main:      mov ax, @data            ; Make data addressable
             mov ds,ax
             mov es,ax                ; For string moves

             call changecow           ; Change "Holstein" to "Daisy"
             retf
             END main

  ; Source file 2:
  ;    In source file 2, structure definition must be available for the
  ; field offsets. (Normally it would be placed in an include file,
  ; then the INCLUDE operator would be used; however, for sake of
  ; clarity, the structure definition has been placed in both files).
  ;    The structure information must be included here to correctly
  ; associate the fields with the offset. The structure name does not
  ; need to be "animals"; however, the structure fields should
  ; correspond.

  animals    STRUC                    ; Structure definition
      cat    db    "catfield      "
      dog    db    "dogfield      "   ; Field widths of 15 characters
      cow    db    "cowfield      "
  animals    ENDS

  .MODEL small

  .DATA
  EXTRN zoo:NEAR                       ; Let assembler know about zoo
  newcow    db     "Daisy         "    ; Replace cow with new name
  lenname   EQU    $ - newcow          ; Length of new name

  .CODE
            PUBLIC changecow           ; Changes cow field to "Daisy"
  changecow PROC
            mov     di, offset zoo.cow ; es:di should now point to
  destination
            mov     si, offset newcow  ; ds:si should now point to the source
            mov     cx, lenname        ; Length of new string
            rep     movsb              ; Do replacement
            ret
  changecow ENDP
            END

Additional query words: kbinf 5.00 5.10 6.00

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Keywords          :  
Technology        : kbMASMsearch kbAudDeveloper kbMASM510 kbMASM600 kbMASM500
Version           : :5.0,5.1,6.0

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