c++, class的大小

 

不为类、对象的函数分配空间；

在类中如果有virtual声明的虚函数，则会隐藏一个指针，该指针指向虚函数表，这对于纯虚函数也是一样；

对于虚继承，还有一个指向父类的指针，该指针为指向虚基类的指针（Pointer to virtual base class）。

 

#include "stdafx.h"
#include <iostream>
using namespace std;

#include "t1.h"

class TNULL
{
};
class Ti
{
    int i;
};
class Tic
{
    int i;
    char c;
};
class Tf
{
    void f(void){}
};
class T_vf
{
    virtual void f(void){}
};
class Tif  
{
public:
    void set(int x)    {i = x;}
private:
    int i;
};
class Ti_vf  
{
public:
    virtual void set(int x)    {i = x;}
private:
    int i;
};
class Ti_v0f  
{
public:
    virtual void set(int x) = 0;
private:
    int i;
};

class Ti_sf  
{
    int i;
    static void sf(void){}
};
class TT
{
    TT(){}
};
class TxT
{
    ~TxT(){}
};

class TTT
{
    TTT(){}
    ~TTT(){}
private:
    Tif* m_pTif;
};

class TTTFFF
{
public:
    TTTFFF()    {
        m_pTif = new Tif;
        m_pTif->set(0);
    }

    ~TTTFFF(){
        delete(m_pTif);
        m_pTif = 0;
    }
    void f1(void){}
    void f2(void){}
    void f3(void){}
private:
    Tif* m_pTif;
};
class TTT_VFFF
{
public:
    TTT_VFFF()    {
        m_pTif = new Tif;
        m_pTif->set(0);
    }

    ~TTT_VFFF(){
        delete(m_pTif);
        m_pTif = 0;
    }
    virtual void f1(void){}
    virtual void f2(void){}
    virtual void f3(void){}
private:
    Tif* m_pTif;
};
void t1(void)
{ 
    cout<<"sizeof(char) = "<<sizeof(char)<<endl;
    cout<<"sizeof(class TNULL) = "<<sizeof(class TNULL)<<endl;
    cout<<"sizeof(class Ti) = "<<sizeof(class Ti)<<endl;
    cout<<"sizeof(class Tic) = "<<sizeof(class Tic)<<endl;

    cout<<"sizeof(class Tf) = "<<sizeof(class Tf)<<endl;
    cout<<"sizeof(class Tif) = "<<sizeof(class Tif)<<endl;
    cout<<"sizeof(class T_vf) = "<<sizeof(class T_vf)<<endl;
    cout<<"sizeof(class Ti_vf) = "<<sizeof(class Ti_vf)<<endl;
    cout<<"sizeof(class Ti_v0f) = "<<sizeof(class Ti_v0f)<<endl;
    
    cout<<"sizeof(class Ti_sf) = "<<sizeof(class Ti_sf)<<endl;
    cout<<"sizeof(class TT) = "<<sizeof(class TT)<<endl;
    cout<<"sizeof(class TxT) = "<<sizeof(class TxT)<<endl;
    cout<<"sizeof(class TTT) = "<<sizeof(class TTT)<<endl;
    cout<<"sizeof(class TTTFFF) = "<<sizeof(class TTTFFF)<<endl;
    cout<<"sizeof(class TTT_VFFF) = "<<sizeof(class TTT_VFFF)<<endl;
    
    TTTFFF t;
    cout<<"sizeof(TTTFFF t) = "<<sizeof(t)<<endl; /*sizeof(TTTFFF t) = 4*/


}
/*
sizeof(char) = 1
sizeof(class TNULL) = 1
sizeof(class Ti) = 4
sizeof(class Tic) = 8
sizeof(class Tf) = 1
sizeof(class Tif) = 4
sizeof(class T_vf) = 4
sizeof(class Ti_vf) = 8
sizeof(class Ti_v0f) = 8
sizeof(class Ti_sf) = 4
sizeof(class TT) = 1
sizeof(class TxT) = 1
sizeof(class TTT) = 4
sizeof(class TTTFFF) = 4
sizeof(class TTT_VFFF) = 8
sizeof(TTTFFF t) = 4
请按任意键继续. . .
*/

 

 

扩展：

1.  C++类的大小 http://www.cnblogs.com/luxiaoxun/archive/2012/09/01/2666395.html

2.  C++ 虚函数表解析 http://blog.csdn.net/haoel/article/details/1948051