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<TD><B> C++類機制的實現細節</B> nightsuns（原作）
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<TD width=500> 類機制 實現細節</TD></TR>
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<P><SPAN id=yuyuzi>為了搞清楚VC中類的實現專門寫了一個最簡單的類，用來觀察它的實現過程，代碼如下：<BR>//
test.cpp : Defines the entry point for the console
application.<BR>//<BR><BR>#include "stdafx.h"<BR>#include
"CTest.h"<BR><BR>int main(int argc, char* argv[])<BR>{<BR>CTest
aTest;<BR>aTest.a(1,2);<BR>return 0;<BR>}<BR><BR>// CTest.h:
interface for the CTest
class.<BR>//<BR>//////////////////////////////////////////////////////////////////////<BR><BR>#if
!defined(AFX_CTEST_H__2CCCDCFC_6C3A_48BC_9CD0_E7A8E63431D9__INCLUDED_)<BR>#define
AFX_CTEST_H__2CCCDCFC_6C3A_48BC_9CD0_E7A8E63431D9__INCLUDED_<BR><BR>#if
_MSC_VER > 1000<BR>#pragma once<BR>#endif // _MSC_VER >
1000<BR><BR>class CTest <BR>{<BR>public:<BR>CTest();<BR>virtual
~CTest();<BR><BR>public:<BR>void b();<BR>void a(int one,int
two);<BR>};<BR><BR>#endif //
!defined(AFX_CTEST_H__2CCCDCFC_6C3A_48BC_9CD0_E7A8E63431D9__INCLUDED_)<BR><BR><BR>//
CTest.cpp: implementation of the CTest
class.<BR>//<BR>//////////////////////////////////////////////////////////////////////<BR><BR>#include
"stdafx.h"<BR>#include
"CTest.h"<BR><BR>//////////////////////////////////////////////////////////////////////<BR>//
Construction/Destruction<BR>//////////////////////////////////////////////////////////////////////<BR><BR>CTest::CTest()<BR>{<BR><BR>}<BR><BR>CTest::~CTest()<BR>{<BR><BR>}<BR><BR>void
CTest::b()<BR>{<BR>printf("b is be called by a");<BR>}<BR><BR>void
CTest::a(int one,int two)<BR>{<BR>printf("call
b");<BR>b();<BR>}<BR><BR><BR><BR><BR>下面是相應的反匯編代碼：<BR>---
D:\myown\test\test.cpp -----------------------------------------------------------------------------------------------<BR>1: //
test.cpp : Defines the entry point for the console
application.<BR>2: //<BR>3:<BR>4: #include
"stdafx.h"<BR>5: #include "CTest.h"<BR>6:<BR>7: int main(int argc,
char* argv[])<BR>8: {<BR>00401050 push ebp<BR>00401051 mov
ebp,esp<BR>00401053 push 0FFh<BR>00401055 push offset
__ehhandler$_main (00410c89)<BR>0040105A mov
eax,fs:[00000000]<BR>00401060 push eax<BR>00401061 mov
dword ptr fs:[0],esp<BR>00401068 sub esp,48h<BR>0040106B
push ebx<BR>0040106C push esi<BR>0040106D
push edi<BR>0040106E lea edi,[ebp-54h]<BR>00401071 mov
ecx,12h<BR>00401076 mov eax,0CCCCCCCCh<BR>0040107B rep
stos dword ptr [edi]<BR><BR>9: CTest aTest;<BR>0040107D lea
ecx,[ebp-10h] //這是用來保存aTest的this指針，因為是局部變量所以是保存在[ebp-10h]中<BR>00401080
call @ILT+30(CTest::CTest)
(00401023) //調用aTest的構造函數，由編譯器自動產生的CALL<BR>00401085 mov dword
ptr [ebp-4],0<BR><BR>10: aTest.a(1,2);<BR>0040108C
push 2<BR>0040108E push 1<BR>00401090 lea
ecx,[ebp-10h] //把aTest的this指針用ecx進行傳遞<BR>00401093
call @ILT+5(CTest::a) (0040100a) <BR>11: return
0;<BR>00401098 mov dword ptr [ebp-14h],0<BR>0040109F mov
dword ptr [ebp-4],0FFFFFFFFh<BR>004010A6 lea
ecx,[ebp-10h] //同樣是this指針<BR>004010A9
call @ILT+25(CTest::~CTest)
(0040101e) //aTest的生存周期到了，自動調用析構函數，同樣是由編譯器分析之后自加上去<BR>004010AE
mov eax,dword ptr [ebp-14h]<BR>12: }<BR>004010B1 mov
ecx,dword ptr [ebp-0Ch]<BR>004010B4 mov dword ptr
fs:[0],ecx<BR>004010BB pop edi<BR>004010BC pop
esi<BR>004010BD pop ebx<BR>004010BE add
esp,54h<BR>004010C1 cmp ebp,esp<BR>004010C3 call __chkesp
(00401670)<BR>004010C8 mov esp,ebp<BR>004010CA pop
ebp<BR>004010CB
ret<BR><BR>下面再來分析一下VC中對函數的調用:<BR>可以看到上面有對三個函數的調用分別為：<BR>00401080
call @ILT+30(CTest::CTest) (00401023)<BR>00401093
call @ILT+5(CTest::a) (0040100a)<BR>004010A9
call @ILT+25(CTest::~CTest)
(0040101e)<BR><BR>可以看到他們都跳到了以@ILT為基的一個地址去了，那么跳過去之后可以看到：<BR>@ILT+0(??_GCTest@@UAEPAXI@Z):<BR>00401005
jmp CTest::`scalar deleting destructor'
(00401130)<BR>@ILT+5(?a@CTest@@QAEXHH@Z):<BR>0040100A jmp
CTest::a (00401230)<BR>@ILT+10(_main):<BR>0040100F jmp main
(00401050)<BR>@ILT+15(?b@CTest@@QAEXXZ):<BR>00401014 jmp
CTest::b (004011e0)<BR>@ILT+20(??_GCTest@@UAEPAXI@Z):<BR>00401019
jmp CTest::`scalar deleting destructor'
(00401130)<BR>@ILT+25(??1CTest@@UAE@XZ):<BR>0040101E jmp
CTest::~CTest (004011a0)<BR>@ILT+30(??0CTest@@QAE@XZ):<BR>00401023
jmp CTest::CTest
(004010f0)<BR><BR>這個@ILT其實就是一個靜態的表，它記錄了一些函數的入口然后跳過去，每個跳轉jmp占一個字節，然后就是一個四字節的內存地址，所以加起為五個字節，這樣就實現了類的機制。<BR><BR>下面再來分析一下，類的成員函數調用另一成員函數的情況：<BR><BR>27:
void CTest::a(int one,int two)<BR>28: {<BR>00401230
push ebp<BR>00401231 mov ebp,esp<BR>00401233 sub
esp,44h<BR>00401236 push ebx<BR>00401237
push esi<BR>00401238 push edi<BR>00401239
push ecx<BR>0040123A lea edi,[ebp-44h]<BR>0040123D mov
ecx,11h<BR>00401242 mov eax,0CCCCCCCCh<BR>00401247 rep
stos dword ptr [edi]<BR>00401249 pop ecx<BR>0040124A mov
dword ptr [ebp-4],ecx<BR>29: printf("call b");<BR>0040124D
push offset string "call b" (00422038)<BR>00401252
call printf (00401830)<BR>00401257 add esp,4<BR>30:
b();<BR>0040125A mov ecx,dword ptr [ebp-4]
//不要想這里的[ebp-4]肯定是this指針，<BR>0040125D call @ILT+15(CTest::b)
(00401014) // 又是@ILT靜態表格<BR>31: }<BR>00401262 pop
edi<BR>00401263 pop esi<BR>00401264 pop ebx<BR>00401265
add esp,44h<BR>00401268 cmp ebp,esp<BR>0040126A
call __chkesp (00401670)<BR>0040126F mov
esp,ebp<BR>00401271 pop ebp<BR>00401272 ret
8 //由于是STDCALLR所以棧是由程序自己來平衡的<BR></SPAN></P><BR></TD></TR></TBODY></TABLE></TD></TR></TBODY></TABLE><BR>
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