陈皓-C++ 对象的内存布局（上）：笔记

单一的一般继承

代码如下：

#include <iostream>using namespace std;class Parent {public:    int iparent;    Parent ():iparent (10) {}    virtual void f() { cout << " Parent::f()" << endl; }    virtual void g() { cout << " Parent::g()" << endl; }    virtual void h() { cout << " Parent::h()" << endl; }    virtual ~Parent() {}};class Child : public Parent {public:    int ichild;    Child():ichild(100) {}    virtual void f() { cout << "Child::f()" << endl; }    virtual void g_child() { cout << "Child::g_child()" << endl; }    virtual void h_child() { cout << "Child::h_child()" << endl; }    virtual ~Child() {}};class GrandChild : public Child{public:    int igrandchild;    GrandChild():igrandchild(1000) {}    virtual void f() { cout << "GrandChild::f()" << endl; }    virtual void g_child() { cout << "GrandChild::g_child()" << endl; }    virtual void h_grandchild() { cout << "GrandChild::h_grandchild()" << endl; }    virtual ~GrandChild() {}};typedef void(*Fun)(void);int main(){    GrandChild gc;    int** pVtab = (int**)&gc;    Fun pFun = NULL;    cout << "[0] GrandChild::_vptr->" << endl;    for (int i=0; (Fun)pVtab[0][i]!=NULL && i<3; i++)    {pFun = (Fun)pVtab[0][i];cout << "    ["<<i<<"] ";pFun();    }    //cout << "[1] Parent.iparent = " << (int)*((int*)(&gc)+1) << endl;    cout << "[1] Child.ichild = " << (int)pVtab[1] << endl;    cout << "[2] Child.ichild = " << (int)pVtab[2] << endl;    cout << "[3] GrandChild.igrandchild = " << (int)pVtab[3] << endl;    return 0;}

for循环中必须有"i<3"的约束条件，否则会报读内存错误。

对"(int)pVtab[1]"的理解：与(int)*((int*)(&gc)+1)是等价的。这是C语言中获取指针指向内容的两种方式：1)解引用; 2)下标操作。

多重继承

代码如下：

/* * multiple_inheritance.h * *  Created on: 2013-10-1 *      Author: Administrator */#ifndef MULTIPLE_INHERITANCE_H_#define MULTIPLE_INHERITANCE_H_#include <iostream>using namespace std;class Base1 {public:    int ibase1;    Base1():ibase1(10) {}    virtual void f() { cout << "Base1::f()" << endl; }    virtual void g() { cout << "Base1::g()" << endl; }    virtual void h() { cout << "Base1::h()" << endl; }virtual ~Base1() {}};class Base2 {public:    int ibase2;    Base2():ibase2(20) {}    virtual void f() { cout << "Base2::f()" << endl; }    virtual void g() { cout << "Base2::g()" << endl; }    virtual void h() { cout << "Base2::h()" << endl; }virtual ~Base2() {}};class Base3 {public:    int ibase3;    Base3():ibase3(30) {}    virtual void f() { cout << "Base3::f()" << endl; }    virtual void g() { cout << "Base3::g()" << endl; }    virtual void h() { cout << "Base3::h()" << endl; }virtual ~Base3() {}};class Derive : public Base1, public Base2, public Base3 {public:    int iderive;    Derive():iderive(100) {}    virtual void f() { cout << "Derive::f()" << endl; }    virtual void g1() { cout << "Derive::g1()" << endl; }virtual ~Derive() {}};#endif /* MULTIPLE_INHERITANCE_H_ */

int main(){    GrandChild gc;    int** pVtab = (int**)&gc;    Fun pFun = NULL;    //Base1    cout << "[0] Base1::_vptr->" << endl;    for (int i=0; (Fun)pVtab[0][i]!=NULL && i<3; i++)    {pFun = (Fun)pVtab[0][i];cout << "    ["<<i<<"] ";pFun();    }    cout << "[1] Base1.ibase1 = " << (int)pVtab[1] << endl;    //Base2    int s = sizeof(Base1)/4; //Derive类继承在Base1类部分所占内存的大小    cout << "[" << s << "]" << "Base2::_vptr->" << endl;    for (int i=0; (Fun)pVtab[s][i]!=NULL && i<3; i++)    {pFun = (Fun)pVtab[s][i];cout << "    ["<<i<<"] ";pFun();    }    cout << "[" << s+1 << "]" << "Base2.ibase2 = " << (int)pVtab[s+1] << endl;    //Base3    s += sizeof(Base2)/4;    cout << "[" << s << "]" << "Base3::_vptr->" << endl;    for (int i=0; (Fun)pVtab[s][i]!=NULL && i<3; i++)    {pFun = (Fun)pVtab[s][i];cout << "    ["<<i<<"] ";pFun();    }    cout << "[" << s+1 << "]" << "Base3.ibase3 = " << (int)pVtab[s+1] << endl;    //Derive    s += sizeof(Base3)/4;    cout << "[" << s << "]" << "Derive.iderive = " << (int)pVtab[s] << endl;    return 0;}

报读内存错误，文章内容未得到验证。通过vs2010查看Derive类对象gc的内存布局和文章说的不一致，如下：