• 派生類對象的體積，等于基類對象的體積，再加上派生類對象自己的成員變量的體積。在派生類對象中，包含著基類對象，而且基類對象的存儲位置位于派生類對象新增的成員變量之前。

class CBase
{
    int v1,v2;
};
class CDerived:public CBase
{
     int v3;
};

• 實例

#include <iostream>
#include <string>
using namespace std;
class CStudent {
private:
    string name;
    string id;//學(xué)號
    char gender;//性別
    int age;
public:
    void PrintInfo();
    void SetInfo(const string & name_,const string & id_,int age_,char gender_);
    string GetName(){return name; }
};
void CStudent::SetInfo(const string &name_, const string &id_, int age_, char gender_){
    name = name_;
    age = age_;
    id = id_;
    gender = gender_;
}
void CStudent::PrintInfo(){
    cout<<"name = "<<name<<" id = "<<id;
}
//本科生類
class CUndergraduateStudent:public CStudent {
private:
    string department;//系
public:
    void  QualifiedForBaoyan(){
        cout<<"qualified for baoyan"<<endl;
    }
    void PrintInfo();
    void SetInfo(const string & name_,const string & id_,int age_,char gender_,const string & department_);
};//派生類的寫法是：類名：public 基類名
void CUndergraduateStudent::SetInfo(const string & name_, const string & id_, int age_, char gender_, const string & department_){
    CStudent::SetInfo(name_, id_, age_, gender_);
    department = department_;
}
void CUndergraduateStudent::PrintInfo(){
    CStudent::PrintInfo();
    cout<<" department = "<<department<<endl;
}
//使用
int main(int argc, const char * argv[]) {
    CUndergraduateStudent a;
    a.SetInfo("aaa", "123", 10, 'f', "物理系");
    cout<<a.GetName()<<endl;
    a.QualifiedForBaoyan();
    a.PrintInfo();    
    return 0;
}