ID Number: Q30887
5.00 5.10 6.00 | 6.00
MS-DOS | 6.00
Summary:
To use a structure, defined in one module with the STRUC (STRUCT in
MASM 6.00) 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