PTR: 指定要操作的数据尺寸

; Test12_1.asm
.386
.model flat, stdcallinclude    windows.inc
include    kernel32.inc
include    masm32.inc
include    debug.inc
includelib kernel32.lib
includelib masm32.lib
includelib debug.lib.dataval db 11h, 22h, 33h, 44h, 55h, 66h, 77h, 88h.code
main procxor eax, eax             ;清空 EAX, 同 mov eax, 0mov eax, dword ptr val   ;PrintHex eax             ;44332211xor eax, eax             ;mov eax, dword ptr val+1 ;PrintHex eax             ;55443322xor eax, eax             ;mov ax, word ptr val     ;PrintHex eax             ;00002211xor eax, eax             ;mov al, byte ptr val     ;PrintHex eax             ;00000011ret
main endp
end main

OFFSET: 获取全局变量或标号的偏移地址

; Test12_2.asm
.386
.model flat, stdcallinclude    windows.inc
include    kernel32.inc
include    masm32.inc
include    debug.inc
includelib kernel32.lib
includelib masm32.lib
includelib debug.lib.datav1 db 'abcdefg', 0v2 dd 11223344h.code
main procPrintHex offset v1    ;00403000PrintHex offset v2    ;00403008PrintHex offset main  ;00401000 - 这里的 main 是个标号ret
;本例中的 offset 不能用 addr 代替
main endp
end main

ADDR: 类似 offset 也是获取变量的地址...

; Test12_3.asm
.386
.model flat, stdcall;include    windows.inc
include    kernel32.inc
includelib kernel32.lib
include    user32.inc
includelib user32.lib.datav1 dd 00434241h ;ABCv2 dd 00636261h ;abc.code
main procinvoke MessageBox, 0, offset v1, offset v2, 0 ;现在 v1、v2 是全局变量invoke MessageBox, 0,   addr v2,   addr v1, 0 ;使用 offset 和 addr 均可invoke ExitProcess, 0
main endp
end main

获取局部变量的地址只能使用 ADDR:

; Test12_4.asm
.386
.model flat, stdcall;include    windows.inc
include    kernel32.inc
includelib kernel32.lib
include    user32.inc
includelib user32.lib.code
main procLOCAL v1,v2mov v1, 00434241hmov v2, 00636261h;invoke MessageBox, 0, offset v1, offset v2, 0  ;offset 不能获取局部变量的地址invoke MessageBox, 0,   addr v2,   addr v1, 0invoke ExitProcess, 0
main endp
end main

OFFSET 和 ADDR 的异同:
1、offset 不能获取局部变量的地址;
2、addr 只能用于调用函数(invoke)时, 不能用于赋值操作;
3、addr 面对局部变量时会转换为 lea 等指令, addr 面对全局变量时则直接调用 offset;
4、在 invoke 中应尽量使用 addr, 其他只用 offset.

; Test12_5.asm
.386
.model flat, stdcallinclude    windows.inc
include    kernel32.inc
include    masm32.inc
include    debug.inc
includelib kernel32.lib
includelib masm32.lib
includelib debug.lib.dataTextAddr equ this byte   ;伪指令 this 可让当前变量和下一个变量同址 szText db 'Asm', 0
.code
main procPrintHex offset szText   ;00403000PrintHex offset TextAddr ;00403000PrintString szText       ;Asmmov [TextAddr], 'a'      ;给 TextAddr 赋值PrintString szText       ;asmret
main endp
end main