c++中类的大小和虚函数调用顺序

声明了一个父类一个子类。

class father{public:father();~father();virtual int getAge();private:int m_age;};class child : public father{public:child();~child();virtual int getAge();private:int m_age;};

实现代码：

#include "test.h"#include <iostream>using namespace std;father::father(){cout<<"father() is Called"<<endl;}father::~father(){cout<<" ~father() is Called "<<endl;};int father::getAge(){m_age = 50;cout<< "father's getAge() is Called age = "<<m_age<<endl;return m_age;}child::child(){cout<<" child() is Called "<<endl;}child::~child(){cout<<" ~child() is Called"<<endl;}int child::getAge(){m_age = 20;cout<< "child's getAge() is Called age = "<<m_age<<endl;return m_age;}

测试代码：

#include <iostream>using namespace std;#include "test.h"int main(){cout<<sizeof(father)<<endl;cout<<"父类的调用顺序"<<endl;father  * pfather = new father();cout<<sizeof(*pfather)<<endl;pfather->getAge();delete pfather;cout<<endl;cout<<sizeof(child)<<endl;cout<<"子类的调用顺序"<<endl;child  * pchild =new child();cout<<sizeof(*pchild)<<endl;pchild->getAge();delete pchild;return 0;}

其中父类的成员变量m_age 占4字节，虚函数表指针占4字节 共有8字节。

子类在父类的基础上还要 ，增加自己的成员变量m_age。

测试结果：