Article ID: 39526
Article Last Modified on 10/17/2003
APPLIES TO
- Microsoft Macro Assembler 5.0
- Microsoft Macro Assembler 5.1 Standard Edition
- Microsoft Macro Assembler 6.0 Standard Edition
- Microsoft Macro Assembler 6.0a
- Microsoft Macro Assembler 6.0b
This article was previously published under Q39526
SUMMARY
You may declare a type with STRUC directive in your MASM module with the same memory-storage template as the "struct" type declared in your C module. You also can declare the variable as external with WORD type if it is a near data, or DWORD type if it is a far data.
In C, the structure may be packed on a 1, 2, or 4-byte boundary. The 2-byte boundary is the default. As a result, the template constructed in your MASM module may not match the memory storage exactly, unless pad bytes are specifically added to the template. See the example below.
In MASM 5.10 and earlier, any template you may create in with the STRUC directive has to have unique field names throughout the module. The field names represent the offset relative to the beginning of the structure. They do not have to be literally the same field names of the structure defined in the C module.
MORE INFORMATION
The sample program below demonstrates this information. It consists of a C module and an Assembler module.
Sample Code
/* Compile options needed: none
*/
struct sample {
char byte_1;
unsigned int word_1;
char byte_2;
unsigned int word_2;
} rec = {0x41, 0xffff, 0x42, 0xeeee};
void proc_rec( void );
void main()
{
proc_rec( );
}
----------------------------------------------------------------------
; Assemble options needed: /Mx (or /Cx with 6.0 and later)
.model small,c
.data
sample STRUC
byte_1 db ? ; if dw is used, next padding byte is not needed.
junk_1 db ? ; necessary padding, unused byte
word_1 dw ?
byte_2 db ?
junk_2 db ? ; necessary padding, unused byte
word_2 dw ?
sample ENDS
EXTRN rec:word ; can use EXTRN rec:sample with 6.0 or later
.code
PUBLIC proc_rec
proc_rec PROC near
MOV ax, rec.word_1
MOV bx, rec.word_2
MOV cl, rec.byte_1
MOV ch, rec.byte_2
RET
proc_rec ENDP
END
Additional query words: kbinf 5.00 5.10 6.00 6.00a 6.00b
Keywords: KB39526
