C++虚继承之内存布局

Posted on 2018-06-26 15:50 沙_shine 阅读(456) 评论(0) 编辑收藏举报

1. 概述

C++虚继承的作用：避免多重继承时因基类的重复而引起的调用二义性.

2. 多重继承 + 非虚继承

#define MemoryLayout_H
#ifdef MemoryLayout_H

class Base
{
public:
    void CommonFunction();
    virtual void VirtualFunction1();
    virtual void VirtualFunction2();
private:
    int m_baseVar1;
    int m_baseVar2;
};

//class Derived1:virtual public Base
class Derived1 :public Base
{
public :
    void Derived1CommonFunction();
    //virtual void VirtualFunction1();
    virtual void VirtualFunction2();
    virtual void Derived1VirtualFunction();
private:
    int m_derived1Var;
};

//class Derived2 :virtual public Base
class Derived2 :public Base
{
public:
    void Derived2CommonFunction();
    //virtual void VirtualFunction1();
    virtual void VirtualFunction2();
    virtual void Derived2VirtualFunction();
private:
    int m_derived2Var;
};

class DerivedDerived :public Derived1,public Derived2
{
public:
    void DerivedCommonFunction();
    //virtual void VirtualFunction1();
    virtual void VirtualFunction2();
    virtual void DerivedDerivedVirtualFunction();
private:
    int m_derivedDerivedVar;
};

#endif/*MemoryLayout_H*/

利用vs2015输出其内存布局分别为：

Base:

Derived1:

Derived2:

DerivedDerived：

内存布局分析：
这里主要分析DerivedDerived类的内存布局：

此继承关系中，若通过DD类实例调用VF1函数，会产生歧义.

3. 多重继承+虚继承

#define MemoryLayout_H
#ifdef MemoryLayout_H

class Base
{
public:
    void CommonFunction();
    virtual void VirtualFunction1();
    virtual void VirtualFunction2();
private:
    int m_baseVar1;
    int m_baseVar2;
};

class Derived1:virtual public Base
//class Derived1 :public Base
{
public :
    void Derived1CommonFunction();
    //virtual void VirtualFunction1();
    virtual void VirtualFunction2();
    virtual void Derived1VirtualFunction();
private:
    int m_derived1Var;
};

class Derived2 :virtual public Base
//class Derived2 :public Base
{
public:
    void Derived2CommonFunction();
    //virtual void VirtualFunction1();
    virtual void VirtualFunction2();
    virtual void Derived2VirtualFunction();
private:
    int m_derived2Var;
};

class DerivedDerived :public Derived1,public Derived2
{
public:
    void DerivedCommonFunction();
    //virtual void VirtualFunction1();
    virtual void VirtualFunction2();
    virtual void DerivedDerivedVirtualFunction();
private:
    int m_derivedDerivedVar;
};

#endif/*MemoryLayout_H*/