定义符号常量(=、EQU、TEXTEQU)

源地址：http://www.cnblogs.com/del/archive/2010/04/07/1706552.html

=、EQU、TEXTEQU 功能差不多, 它们定义的符号都将在编译前辈替换成它们指定的常量值.

相比之下 EQU 更好用些.

---

= 举例

---

; Test13_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
    n = 1      ; = 伪指令只能定义整数或整数表达式
    n = n + 1  ; 可重复定义
.code
main proc
    PrintDec n ;2
    ret
main endp
end main

EQU 例一

---

; Test13_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
    num1 equ 2         ; equ 可以定义整数和整数表达式
    num2 equ 3         ; 它不能像 = 一样重复定义
    num3 equ num1+num2 ; (我尝试了重复定义, 竟然有时也可以, 只是偶尔)
    
    txt  equ <'Asm'>   ; 可用 equ 定义字符串, 应使用 <>
    
    szTxt db txt, 0    ; 使用 equ 定义的常量
.code
main proc
    PrintDec num3     ;5
    PrintString szTxt ;Asm
    ret
main endp
end main

EQU 例二

---

; Test13_3.asm
.386
.model flat, stdcall

include    windows.inc
include    kernel32.inc
includelib kernel32.lib
include    user32.inc
includelib user32.lib

; 用 equ 给函数重命名
Msg  equ MessageBox
Exit equ   ;尖括号可保证字符串的完整、并避免和关键字冲突（是否类似于c中宏定义的()？）
; 甚至代替整个表达式
ShowMsg equ <invoke MessageBox, NULL, addr szMsg, addr szCaption, MB_OK>

.data
    szMsg     db 'Hello World!', 0
    szCaption db 'Hi', 0
.code
main proc
    invoke Msg, NULL, addr szMsg, addr szCaption, MB_OK
    ShowMsg
    invoke Exit, NULL
main endp
end main

用 TEXTEQU 重做上一个例子, 完全可行:

---

; Test13_4.asm
.386
.model flat, stdcall

include    windows.inc
include    kernel32.inc
includelib kernel32.lib
include    user32.inc
includelib user32.lib

Msg  textequ MessageBox
Exit textequ 
ShowMsg textequ <invoke MessageBox, NULL, addr szMsg, addr szCaption, MB_OK>

.data
    szMsg     db 'Hello World!', 0
    szCaption db 'Hi', 0
.code
main proc
    invoke Msg, NULL, addr szMsg, addr szCaption, MB_OK
    ShowMsg
    invoke Exit, NULL
main endp
end main

用 TEXTEQU 重做 EQU 的第一个例子(Test13_2.asm), 有区别:

---

; Test13_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
    
.data
    num1 equ 2               ; 这里的 equ 换做 textequ 不行
    num2 textequ <3>         ; 如果用 textequ 定义整数或表达式也要放在 <> 中
    num3 textequ  ; 这曾是 num3 equ num1+num2
    
    txt  textequ <'Asm'>     ;
    txt  textequ <'Delphi'>  ; textequ 可重复定义
    
    szTxt db txt, 0
.code
main proc
    PrintDec num3     ;5
    PrintString szTxt ;Delphi
    ret
main endp
end main