学 Win32 汇编[14]: 使用中括号 []

[地址] 是取地址指向的内容:

---

; Test14_1.asm

.386

.model flat, stdcall



include    windows.inc

include    kernel32.inc

include    masm32.inc

include    debug.inc

includelib kernel32.lib

includelib masm32.lib

includelib debug.lib

    

.data

    dwVal dd 123

.code

main proc

    PrintDec offset dwVal ;4206592 - 这是变量 dwVal 的地址

    PrintDec dwVal        ;123     - 这是变量值

    

    lea ebx, dwVal        ;Lea 是专门获取地址的指令, 这同 mov ebx, offset dwVal

    PrintDec ebx          ;4206592

    

    mov eax, [ebx]        ;现在 ebx 中放着 dwVal 变量的地址, [ebx] 则表示地址指向的值

    PrintDec eax          ;123

    ret

main endp

end main


 
   

地址指向的是什么数据?

---

; Test14_2.asm

.386

.model flat, stdcall



include    windows.inc

include    kernel32.inc

include    masm32.inc

include    debug.inc

includelib kernel32.lib

includelib masm32.lib

includelib debug.lib

    

.data

    wVal dw 123

.code

main proc

    lea ebx, wVal  ;把变量 wVal 的地址放到 ebx

    

    ;但现在 wVal 中放着的是 word 类型的数据, 而 [ebx] 默认是取 32 位的数据

    ;这可通过伪指令 ptr 指定数据大小

    ;同时需要把接收着换成 16 的(如 ax), 因为 mov 要求两个操作数的大小须一致

    xor eax, eax  ;清空 eax

    mov ax, word ptr [ebx]

    PrintDec eax  ;123

    

    ;也可以直接使用 movzx, 它可以从小到大(movzx r16/r32, r/8/r16/m8/m16)

    movzx eax, word ptr [ebx]

    PrintDec eax  ;123

    ret

main endp

end main


 
   

[] 一般用于数组:

---

; Test14_3.asm

.386

.model flat, stdcall



include    windows.inc

include    kernel32.inc

include    masm32.inc

include    debug.inc

includelib kernel32.lib

includelib masm32.lib

includelib debug.lib

    

.data

    wArr dw 11,22,33

.code

main proc

    ;把数组 bArr 的起始地址放到 ebx, 并获取数组元素:

    lea ebx, wArr  

    movzx eax, word ptr [ebx]

    movzx ecx, word ptr [ebx+2]

    movzx edx, word ptr [ebx+4]

    PrintDec eax  ;11

    PrintDec ecx  ;22

    PrintDec edx  ;33

    

    ;这样做更好些:

    lea ebx, wArr

    mov esi, type wArr ;把元素大小放在 esi

    movzx eax, word ptr [ebx]

    movzx ecx, word ptr [ebx + esi * 1]

    movzx edx, word ptr [ebx + esi * 2]

    PrintDec eax  ;11

    PrintDec ecx  ;22

    PrintDec edx  ;33

    

    ;这样也行:

    lea ebx, wArr

    mov esi, type wArr ;把元素大小放在 esi

    movzx eax, word ptr [ebx]

    movzx ecx, word ptr [ebx][esi * 1]

    movzx edx, word ptr [ebx][esi * 2]

    PrintDec eax  ;11

    PrintDec ecx  ;22

    PrintDec edx  ;33

    

    ;如果直接使用变量就更像高级语言里的数组了:

    lea ebx, wArr

    mov esi, type wArr ;把元素大小放在 esi

    movzx eax, word ptr wArr

    movzx ecx, word ptr wArr[esi * 1]

    movzx edx, word ptr wArr[esi * 2]

    PrintDec eax  ;11

    PrintDec ecx  ;22

    PrintDec edx  ;33



    ret

main endp

end main


 
   

当然也可以写入数组:

---

; Test14_4.asm

.386

.model flat, stdcall



include    windows.inc

include    kernel32.inc

include    masm32.inc

include    debug.inc

includelib kernel32.lib

includelib masm32.lib

includelib debug.lib

    

.data

    wArr dw 11h ,22h, 33h

.code

main proc

    DumpMem offset wArr, sizeof wArr ;11 00 22 00 33 00

    lea ebx, wArr  

    mov word ptr [ebx],   44h

    mov word ptr [ebx+2], 55h

    mov word ptr [ebx+4], 66h

    DumpMem offset wArr, sizeof wArr ;44 00 55 00 66 00

    

    ;或者:

    mov word ptr wArr,    77h

    mov word ptr wArr[2], 88h

    mov word ptr wArr[4], 99h

    DumpMem offset wArr, sizeof wArr ;77 00 88 00 99 00

    ret

main endp

end main


 
   

好像 [] 不能直接是变量或常数(变量后面跟的 [] 除外).

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