用汇编的眼光看C++（之类继承）
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继承是类的一个基本属性，可是在类的继承过程中，函数是怎么初始化？怎么析构的呢？我们不妨看看下面这样的一段代码？
copy to clipboardprint?class employee
{
public:
employee() { printf("employee()!/n");}
~employee() { printf("~employee()!/n");}
};
class manager : public employee
{
public:
manager() { printf("manager()!/n");}
~manager() { printf("~maneger()!/n");}
};
class employee
{
public:
employee() { printf("employee()!/n");}
~employee() { printf("~employee()!/n");}
};
class manager : public employee
{
public:
manager() { printf("manager()!/n");}
~manager() { printf("~maneger()!/n");}
}; 看到上面的代码，相信大家也明白了，我们定义了这样一个类。基类是empoyee，继承类是manager。我们看到manager是一种特殊的employee，那么在内存构建和析构的时候函数又是怎么安排的呢？
copy to clipboardprint?74: manager m;
00401268 lea ecx,[ebp-4]
0040126B call @ILT+60(manager::manager) (00401041)
75: }
00401270 lea ecx,[ebp-4]
00401273 call @ILT+0(manager::~manager) (00401005)
00401278 pop edi
00401279 pop esi
0040127A pop ebx
0040127B add esp,44h
0040127E cmp ebp,esp
00401280 call __chkesp (00408760)
00401285 mov esp,ebp
00401287 pop ebp
74: manager m;
00401268 lea ecx,[ebp-4]
0040126B call @ILT+60(manager::manager) (00401041)
75: }
00401270 lea ecx,[ebp-4]
00401273 call @ILT+0(manager::~manager) (00401005)
00401278 pop edi
00401279 pop esi
0040127A pop ebx
0040127B add esp,44h
0040127E cmp ebp,esp
00401280 call __chkesp (00408760)
00401285 mov esp,ebp
00401287 pop ebp
我们发现manager的构造和析构其实也简单。构造函数其实就是在变量出现的时候进行构造。那什么时候析构呢？也就在函数快结束的时候进行析构。下面我们可以进一步讨论在manager的构造和析构究竟是怎么做的？
copy to clipboardprint?65: class manager : public employee
66: {
67: public:
68: manager() { printf("manager()!/n");}
004012A0 push ebp
004012A1 mov ebp,esp
004012A3 sub esp,44h
004012A6 push ebx
004012A7 push esi
004012A8 push edi
004012A9 push ecx
004012AA lea edi,[ebp-44h]
004012AD mov ecx,11h
004012B2 mov eax,0CCCCCCCCh
004012B7 rep stos dword ptr [edi]
004012B9 pop ecx
004012BA mov dword ptr [ebp-4],ecx
004012BD mov ecx,dword ptr [ebp-4]
004012C0 call @ILT+40(employee::employee) (0040102d)
004012C5 push offset string "manager()!/n" (00431020)
004012CA call printf (004086e0)
004012CF add esp,4
004012D2 mov eax,dword ptr [ebp-4]
004012D5 pop edi
004012D6 pop esi
004012D7 pop ebx
004012D8 add esp,44h
004012DB cmp ebp,esp
004012DD call __chkesp (00408760)
004012E2 mov esp,ebp
004012E4 pop ebp
004012E5 ret
65: class manager : public employee
66: {
67: public:
68: manager() { printf("manager()!/n");}
004012A0 push ebp
004012A1 mov ebp,esp
004012A3 sub esp,44h
004012A6 push ebx
004012A7 push esi
004012A8 push edi
004012A9 push ecx
004012AA lea edi,[ebp-44h]
004012AD mov ecx,11h
004012B2 mov eax,0CCCCCCCCh
004012B7 rep stos dword ptr [edi]
004012B9 pop ecx
004012BA mov dword ptr [ebp-4],ecx
004012BD mov ecx,dword ptr [ebp-4]
004012C0 call @ILT+40(employee::employee) (0040102d)
004012C5 push offset string "manager()!/n" (00431020)
004012CA call printf (004086e0)
004012CF add esp,4
004012D2 mov eax,dword ptr [ebp-4]
004012D5 pop edi
004012D6 pop esi
004012D7 pop ebx
004012D8 add esp,44h
004012DB cmp ebp,esp
004012DD call __chkesp (00408760)
004012E2 mov esp,ebp
004012E4 pop ebp
004012E5 ret
我们发现，manager的构造里面添加了employee的缺省构造函数，那么析构函数呢？
copy to clipboardprint?69: ~manager() { printf("~maneger()!/n");}
00401350 push ebp
00401351 mov ebp,esp
00401353 sub esp,44h
00401356 push ebx
00401357 push esi
00401358 push edi
00401359 push ecx
0040135A lea edi,[ebp-44h]
0040135D mov ecx,11h
00401362 mov eax,0CCCCCCCCh
00401367 rep stos dword ptr [edi]
00401369 pop ecx
0040136A mov dword ptr [ebp-4],ecx
0040136D push offset string "~maneger()!/n" (00431040)
00401372 call printf (004086e0)
00401377 add esp,4
0040137A mov ecx,dword ptr [ebp-4]
0040137D call @ILT+5(employee::~employee) (0040100a)
00401382 pop edi
00401383 pop esi
00401384 pop ebx
00401385 add esp,44h
00401388 cmp ebp,esp
0040138A call __chkesp (00408760)
0040138F mov esp,ebp
00401391 pop ebp
00401392 ret
69: ~manager() { printf("~maneger()!/n");}
00401350 push ebp
00401351 mov ebp,esp
00401353 sub esp,44h
00401356 push ebx
00401357 push esi
00401358 push edi
00401359 push ecx
0040135A lea edi,[ebp-44h]
0040135D mov ecx,11h
00401362 mov eax,0CCCCCCCCh
00401367 rep stos dword ptr [edi]
00401369 pop ecx
0040136A mov dword ptr [ebp-4],ecx
0040136D push offset string "~maneger()!/n" (00431040)
00401372 call printf (004086e0)
00401377 add esp,4
0040137A mov ecx,dword ptr [ebp-4]
0040137D call @ILT+5(employee::~employee) (0040100a)
00401382 pop edi
00401383 pop esi
00401384 pop ebx
00401385 add esp,44h
00401388 cmp ebp,esp
0040138A call __chkesp (00408760)
0040138F mov esp,ebp
00401391 pop ebp
00401392 ret
我们发现，manager构造的时候employee率先构造，然后打印manager；析构的时候，恰恰相反，manager首先析构自己，然后在再调用employee的析构函数，上面的汇编代码证明了一切。
