虚继承不明确继承疑问

最新推荐文章于 2024-02-16 11:02:56 发布

原创最新推荐文章于 2024-02-16 11:02:56 发布 · 906 阅读

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#include<iostream> #include<string> using namespace std; class Base1 { public: Base1():i(1){} virtual void f() { cout << "Base1::f" << endl; } virtual void g() { cout << "Base1::g" << endl; } virtual void h() { cout << "Base1::h" << endl; } int i; }; class Base2:public virtual Base1{ public: virtual void f() { cout << "Base2::f" << endl; } virtual void f1() { cout << "Base2::f1" << endl; } virtual void g() { cout << "Base2::g" << endl; } //virtual void h() { cout << "Base2::h" << endl; }//取消注释该行，编译失败，因在虚基类的虚函数表中不知道该填入Base2:h还是Base3:h /*如采用 class Base1{} class Base2{} class Base3{} class Derive : public Base1,public Base2, public Base3{} 这样的结构则没此问题。*/ }; class Base3:public virtual Base1 { public: virtual void f() { cout << "Base3::f" << endl; } virtual void g() { cout << "Base3::g" << endl; } virtual void h() { cout << "Base3::h" << endl; } }; class Derive : public Base2, public Base3 { public: virtual void f() { cout << "Derive::f" << endl; } virtual void g() { cout << "Derive::g" << endl; } virtual void g1() { cout << "Derive::g1" << endl; } }; typedef void(*Fun)(void); int main() { typedef void (*Func)(); Func pFun; Derive d; int **pVtab =(int**)&d; cout << "[0] Base2->vfptr:" << endl; pFun =(Func)pVtab[0][0]; cout << " [0] "; pFun(); pFun =(Func)pVtab[0][1]; cout << " [1] "; pFun(); pFun =(Func)pVtab[0][2]; cout << " [2] "; cout << pFun << endl; cout << "[1] Base2->vbptr:" << endl; pFun =(Func)pVtab[1][0]; cout << " [0] "; cout << pFun << endl; pFun =(Func)pVtab[1][1]; cout << " [1] "; cout << pFun << endl; cout << "[2] Base3->vbptr:" << endl; pFun =(Func)pVtab[2][0]; cout << " [0] "; cout << pFun << endl; pFun =(Func)pVtab[2][1]; cout << " [0] "; cout << pFun << endl; cout << "[3] Base1->vfptr:" << endl; pFun =(Func)pVtab[3][0]; cout << " [0] "; pFun(); pFun =(Func)pVtab[3][1]; cout << " [1] "; pFun(); pFun =(Func)pVtab[3][2]; cout << " [2] "; pFun(); pFun =(Func)pVtab[3][3]; cout << " [3] "; cout << pFun << endl; cout << "[4] Base1->i:"<< *((int*)(&d)+4)<< endl; //cout << (int*)*((int*)(&d)+2)<< endl; //cout << *(int*)*((int*)(&d)+2)<< endl; //cout << (int*)*((int*)(&d)+2)<< endl; //打印地址时以十六进制打印 //cout << *((int*)(&d)+2)<< endl; system("pause"); return 0; }

Derived的内存布局：

class Derive size(20):
+---
| +--- (base class Base2)
0 | | {vfptr}
4 | | {vbptr}
| +---
| +--- (base class Base3)
8 | | {vbptr}
| +---
+---
+--- (virtual base Base1)
12 | {vfptr}
16 | i
+---
Derive::$vftable@Base2@:
| &Derive_meta
| 0
0 | &Base2::f1
1 | &Derive::g1
Derive::$vbtable@Base2@:
0 | -4
1 | 8 (Derived(Base2+4)Base1)
Derive::$vbtable@Base3@:
0 | 0
1 | 4 (Derived(Base3+0)Base1)
Derive::$vftable@Base1@:
| -12
0 | &Derive::f
1 | &Derive::g
2 | &Base3::h//不注释掉virtual void h(){ cout<<"Base2::h"<<endl;},则因该处不知填入Base2::h,还是Base3::h,而编译不了。
Derive::f this adjustor: 12
Derive::g this adjustor: 12
Derive::g1 this adjustor: 0
vbi: class offset o.vbptr o.vbte fVtorDisp
Base1 12 4 4 0