学 Win32 汇编[9]: 子过程中的变量声明

定义子过程的伪指令: PROC、ENDP

---

; Test9_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

.code
    ;子过程 proc1:
    proc1 proc
        PrintText 'proc1'
    proc1 endp
    
    ;子过程 proc2:
    proc2 proc
        PrintText 'proc2'
    proc2 endp
    
    ;子过程 proc3:
    proc3 proc
        PrintText 'proc3'
    proc3 endp

    ret
end proc1  ;end 后面的 proc1 是入口的子过程名; 这也就是指定主过程.

;可以把 end proc1 分别换做 end proc2 和 end proc3 尝试,
;如果这是一个供其他程序调用的代码文件, 那么 end 后面就不需要指定.

模仿 C 语言的样子, 以后的程序结构应该这样:

---

; Test9_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
    szText db 'Hello World!', 0DH, 0AH, 0
    
.code
main proc
    PrintString szText  ;Hello World!
    ret
main endp
end main

局部变量要用 local 声明, 和全局变量区别不小:

---

; Test9_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

.code
main proc
    ;局部变量中的类型不能使用缩写
    LOCAL v1: dword
    
    ;可用逗号间隔写在一行
    LOCAL v2: dword, v3: dword
    
    ;不指定类型时默认 DWORD(在 Win32 下)
    LOCAL v4
    
    ;数组
    LOCAL v5[3]: dword
    
    ;在手动初始化前, 局部变量中都是些垃圾值:
    PrintDec v1
    PrintDec v2
    PrintDec v3
    PrintDec v4
    mov eax, v5[0]
    PrintDec eax
    ret
main endp
end main

调用子过程:

---

; Test9_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

.code
;
proc1 proc
    PrintDec 1
    ret
proc1 endp
;
proc2 proc
    PrintDec 2
    ret
proc2 endp
;
main proc
    PrintDec 0
    call proc2
    call proc1
    ret
main endp
end main

;注释:
;最后一行 end main 决定了子过程将被率先调用, 这样它就成了主过程
;然后主过程又通过 call 指令顺序调用了 proc2、proc1
;这样最后的显示结果将是: 0 / 2 / 1
;子过程应该用 ret 指令返回

一个求和函数的例子:

---

; Test9_5.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

.code
;求和的函数, 函数返回值在 eax
;sum proc v1:dword, v2:dword, v3:dword
sum proc v1, v2, v3 ;这是上一行的简化, 其类型也是默认为 dword
    mov eax, v1
    add eax, v2
    add eax, v3
    ret
sum endp
;
main proc
    invoke sum, 11, 22, 33
    PrintDec eax  ;66
    ret
main endp
end main