A Structure Template Can Be Referenced in a MASM Program (74924)

SUMMARY

With the Microsoft Macro Assembler (MASM), if a structure type is declared but no instance of the structure is ever defined, the assembler will still permit access to the structure.

This is expected behavior for the assembler. A reference to a structure field in this manner is equivalent to taking the offset of the field from the beginning of the structure.

MORE INFORMATION

The sample code below illustrates this situation. The example declares an "animal" structure type, but does not define an instance of the structure. A reference to this structure type is then made in the following line:

   mov ax, animal.dog

As described above, the reference to animal.dog just generates the offset of the field, dog, from the beginning of the structure; therefore, this line is effectively the same as the statement "mov ax, 2".

Sample Code

; Assemble options needed: none

        .MODEL SMALL

        animal   struc
        cat     dw  11
        dog     dw  12
        animal   ends

        .CODE
start:  mov ax, @data
        mov ds, ax
        mov ax, animal.dog
        END start