内容载入中...
3. VB6的控制结构
下面要提到的vb的控制结构语句有：if语句，select case语句，while语句，do语句，
for语句。
1)if语句
if语句的典型语法是:
If 条件1 Then
语句块1
ElseIf 条件2 Then
语句块2
Else
语句块3
End If
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
代码：
Dim a //注意：这里定义的是变体变量。
//如果不用变体变量，编译器将优化掉太多的代码。
//当你熟悉变体类型后，其他的将很容易分析 ^_^
a = 5
If a < 5 Then
MsgBox ("a < 5")
ElseIf a = 5 Then
MsgBox ("a = 5")
Else
MsgBox ("a > 5")
End If
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
反汇编代码：
00401A72 XOR ESI,ESI
00401A74 MOV EDI,5
00401A79 MOV DWORD PTR SS:[EBP-74],ESI
00401A7C LEA EDX,DWORD PTR SS:[EBP-74]
00401A7F LEA ECX,DWORD PTR SS:[EBP-24]
00401A82 MOV DWORD PTR SS:[EBP-24],ESI
00401A85 MOV DWORD PTR SS:[EBP-34],ESI ----> 这些变量是为 MsgBox 使用的
00401A88 MOV DWORD PTR SS:[EBP-44],ESI |
00401A8B MOV DWORD PTR SS:[EBP-54],ESI |
00401A8E MOV DWORD PTR SS:[EBP-64],ESI ---
00401A91 MOV DWORD PTR SS:[EBP-6C],EDI // 5
00401A94 MOV DWORD PTR SS:[EBP-74],2 //整数类型
00401A9B CALL DWORD PTR DS:[<&MSVBVM60.__vbaVarMove>]//赋值
//到这里 a = 5 //[ebp-24]
00401AA1 LEA EAX,DWORD PTR SS:[EBP-24]
00401AA4 LEA ECX,DWORD PTR SS:[EBP-74]
00401AA7 MOV EBX,8002
00401AAC PUSH EAX
00401AAD PUSH ECX
00401AAE MOV DWORD PTR SS:[EBP-6C],EDI // 5
00401AB1 MOV DWORD PTR SS:[EBP-74],EBX // 8002
00401AB4 CALL DWORD PTR DS:[<&MSVBVM60.__vbaVarTstLt>] // a < 5 ?
00401ABA TEST AX,AX
00401ABD JE SHORT 工程2.00401AE4 //不小于则跳走
00401ABF MOV ECX,80020004
00401AC4 MOV EAX,0A
00401AC9 MOV DWORD PTR SS:[EBP-5C],ECX
00401ACC MOV DWORD PTR SS:[EBP-64],EAX
00401ACF MOV DWORD PTR SS:[EBP-4C],ECX
00401AD2 MOV DWORD PTR SS:[EBP-54],EAX
00401AD5 MOV DWORD PTR SS:[EBP-3C],ECX
00401AD8 MOV DWORD PTR SS:[EBP-44],EAX
00401ADB MOV DWORD PTR SS:[EBP-6C],工程2.004016C4; UNICODE "a < 5"
00401AE2 JMP SHORT 工程2.00401B63
00401AE4 LEA ECX,DWORD PTR SS:[EBP-24]
00401AE7 LEA EDX,DWORD PTR SS:[EBP-74]
00401AEA PUSH ECX
00401AEB PUSH EDX
00401AEC MOV DWORD PTR SS:[EBP-6C],EDI // 5
00401AEF MOV DWORD PTR SS:[EBP-74],EBX // 8002
00401AF2 CALL DWORD PTR DS:[<&MSVBVM60.__vbaVarTstEq>]// a = 5 ?
00401AF8 TEST AX,AX
00401AFB MOV ECX,80020004
00401B00 MOV EAX,0A
00401B05 MOV DWORD PTR SS:[EBP-5C],ECX
00401B08 MOV DWORD PTR SS:[EBP-64],EAX
00401B0B MOV DWORD PTR SS:[EBP-4C],ECX
00401B0E MOV DWORD PTR SS:[EBP-54],EAX
00401B11 MOV DWORD PTR SS:[EBP-3C],ECX
00401B14 MOV DWORD PTR SS:[EBP-44],EAX
00401B17 JE SHORT 工程2.00401B5C //不相等则跳走
00401B19 LEA EDX,DWORD PTR SS:[EBP-74]
00401B1C LEA ECX,DWORD PTR SS:[EBP-34]
00401B1F MOV DWORD PTR SS:[EBP-6C],工程2.004016D4; UNICODE "a = 5"
00401B26 MOV DWORD PTR SS:[EBP-74],8
00401B2D CALL DWORD PTR DS:[<&MSVBVM60.__vbaVarDup>]
00401B33 LEA EAX,DWORD PTR SS:[EBP-64]
00401B36 LEA ECX,DWORD PTR SS:[EBP-54]
00401B39 PUSH EAX
00401B3A LEA EDX,DWORD PTR SS:[EBP-44]
00401B3D PUSH ECX
00401B3E PUSH EDX
00401B3F LEA EAX,DWORD PTR SS:[EBP-34]
00401B42 PUSH ESI
00401B43 PUSH EAX
00401B44 CALL DWORD PTR DS:[<&MSVBVM60.#595>]; MSVBVM60.rtcMsgBox
00401B4A LEA ECX,DWORD PTR SS:[EBP-64]
00401B4D LEA EDX,DWORD PTR SS:[EBP-54]
00401B50 PUSH ECX
00401B51 LEA EAX,DWORD PTR SS:[EBP-44]
00401B54 PUSH EDX
00401B55 LEA ECX,DWORD PTR SS:[EBP-34]
00401B58 PUSH EAX
00401B59 PUSH ECX
00401B5A JMP SHORT 工程2.00401B9D
// 其他条件满足则执行这里
00401B5C MOV DWORD PTR SS:[EBP-6C],工程2.004016E4; UNICODE "a > 5"
00401B63 LEA EDX,DWORD PTR SS:[EBP-74]
00401B66 LEA ECX,DWORD PTR SS:[EBP-34]
00401B69 MOV DWORD PTR SS:[EBP-74],8
00401B70 CALL DWORD PTR DS:[<&MSVBVM60.__vbaVarDup>]
00401B76 LEA EDX,DWORD PTR SS:[EBP-64]
00401B79 LEA EAX,DWORD PTR SS:[EBP-54]
00401B7C PUSH EDX
00401B7D LEA ECX,DWORD PTR SS:[EBP-44]
00401B80 PUSH EAX
00401B81 PUSH ECX
00401B82 LEA EDX,DWORD PTR SS:[EBP-34]
00401B85 PUSH ESI
00401B86 PUSH EDX
00401B87 CALL DWORD PTR DS:[<&MSVBVM60.#595>]; MSVBVM60.rtcMsgBox
流程大概如此。上面出现了一些VB内部函数，如果你不太熟悉那些函数的意义，可以
到DFCG上下载一份我整理的vb内部函数。
===========================================================
2)select case 语句
select case 语句的语法如下：
Select Case 测试表达式
Case 表达式列表1
语句块1
Case 表达式列表2
语句块2
......
Case Else
语句块n
End Select
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
代码：
Dim a, b
a = 5
Select Case a
Case 3
b = "3"
Case 5
b = "5"
Case Else
b = "0"
End Select
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
反汇编代码(速度优化编译）
00401A2F XOR ESI,ESI // 用来初始化变量
00401A31 LEA EDX,DWORD PTR SS:[EBP-44]
00401A34 MOV DWORD PTR SS:[EBP-44],ESI
00401A37 LEA ECX,DWORD PTR SS:[EBP-24]
00401A3A MOV DWORD PTR SS:[EBP-24],ESI
00401A3D MOV DWORD PTR SS:[EBP-34],ESI
document.getElementById('loading').style.display="none";
