c++ 类继承中父类和子类的数据关系

示例代码:
 class Tbase
{
public:
 Tbase();
 virtual ~Tbase();
public:
 void display()
 {
  printf("%d,%d",i,j);
 }
 
 void set(int i1,int j1)
 {
  i=i1;j=j1;
 }
 Tbase* Create()
 {
  return new Tbase();
 }
private:
 int i;
 int j;
public:
 int pi;
};
 
class FromTbase:public Tbase
{
public:
 FromTbase();
 ~FromTbase();
 
public:
 void display()
 {
  printf("%d,%d",i,k);
 }
 
 void set1(int i1,int k1)
 {
  i=i1;k=k1;
 }
 FromTbase* CreateError()  //错误的生成的方式
 {
  return (FromTbase*)Tbase::Create();
 }
 FromTbase* CreateRight()
 {
  FromTbase* p=new FromTbase();
  p->set(20,30);
  return p;
 }
 
 void TheFun()
 {
  Tbase::set(100,200);
  Tbase::display();
  printf("/n%d,%d,%d",i,k,Tbase::pi);
 }
 
private:
 int i;
 int k;
};
 
Tbase::Tbase():i(10),j(20),pi(5)
{
}
Tbase::~Tbase(){}
 
FromTbase::FromTbase():i(30),k(40),Tbase()
{}
 
FromTbase::~FromTbase(){}
 
int _tmain(int argc, _TCHAR* argv[])
{
 FromTbase from;
 from.TheFun();
 return 0;
}

 
1.从基类继承
FromTBase  从Tbase继承过来.
这意味着FromTBase   拥有一份自己的Tbase的数据拷贝.对于这一份的拷贝的读写的访问权限
请查看相关书和文章.

2. 数据和函数的定义
FromTBase  和 Tbase 可以定义同名的变量和函数.
至于virtual 函数,有特殊作用,请查看相关书和文章
.
3.TheFun()
访函数示意了如何该问FromTBase对象对其所拥有的Tbase拷贝的访问.
 
4. FromTBase   的对外接口由FromTBase 的公有接口和其继承过来的公有接口两部分来决定.
 
继承过来的那一部分是公有接口请要看相关书和文章.
 
5.动态生成
注意到
CreateError() 这是一种很糟糕的想法.
其实质相当于:
在FromBase的一个成员中:
Tbase base;
FromBase* p=(FromBase*)&base;
 
而实质上:base中只有 Tbase类的数据,而没有FromBase中的数据,
这样会倒导访问越界.
如在main函数中写:
 FromTbase from;
 FromTbase* p=from.CreateError();
 p->set1(20,30);  
 //在小的程序中,这样可能会运行正常,但其实已隐藏非法访问,在大型程序中则会由此产生该问冲突
 
为了进行测试.重新定义类如下:
class Tbase
{
public:
 Tbase();
 virtual ~Tbase();
public:
 void display()
 {
  printf("%d,%d",i,j);
 }
 
 void set(int i1,int j1)
 {
  i=i1;j=j1;
 }
 Tbase* Create()
 {
  return new Tbase();
 }
private:
 int i;
 int j;
public:
 int pi;
};
 
class FromTbase:public Tbase
{
public:
 FromTbase();
 ~FromTbase();
 
public:
 void display()
 {
  printf("%d,%d",i,k);
 }
 
 void set1(int i1,int k1)
 {
  i=i1;k=k1;
 }
 FromTbase* CreateError()  //错误的生成的方式
 {
  return (FromTbase*)Tbase::Create();
 }
 FromTbase* CreateRight()
 {
  FromTbase* p=new FromTbase();
  p->set(20,30);
  return p;
 }
 
 void TheFun()
 {
  Tbase::set(100,200);
  Tbase::display();
  printf("/n%d,%d,%d",i,k,Tbase::pi);
 }
 
 void setChar()
 {
  test[1000]='c';
 }
private:
 int i;
 int k;
 char test[2000];
};
 
Tbase::Tbase():i(10),j(20),pi(5)
{
}
Tbase::~Tbase(){}
 
FromTbase::FromTbase():i(30),k(40),Tbase()
{}
 
FromTbase::~FromTbase(){}
 
int _tmain(int argc, _TCHAR* argv[])
{
 FromTbase from;
 from.TheFun();
 
 FromTbase* p=from.CreateRight();
 p->setChar();
 FromTbase* p1=from.CreateRight();
 p1->setChar();

 p=from.CreateError();
 p->setChar();        //运行到此外会发生该问冲突
p1=from.CreateError();
 p1->setChar();
 

 return 0;
 
}
 
6.关于虚函数和纯虚函数
查看书和文章
 
7. 利用虚函数实现动态运行时调用举例
#include "stdafx.h"

 
class Tbase
{
public:
 Tbase();
 virtual ~Tbase();
public:
 virtual Set()
 {
  Buffer[999]='c';
 }
 virtual void SetExample(Tbase* p)
 {
  p->Set();
 }
private:
 char Buffer[1000];
};
 
class FromTbase:public Tbase
{
public:
 FromTbase();
 ~FromTbase();
 virtual Set()
 {
  i=20;
  Tbase::Set();
 }
public:
 int i;
};
 
Tbase::Tbase()
{}
Tbase::~Tbase(){}
 
FromTbase::FromTbase():Tbase()
{}
 
FromTbase::~FromTbase(){}
 

typedef std::map<int,FromTbase*> TMap;
 
int _tmain(int argc, _TCHAR* argv[])
{
 
 FromTbase from;
 from.SetExample(&from);
 
 return 0;
 
}
 

7. 利用虚函数实现动态运行时调用举例

#include "stdafx.h"

 

class Tbase
{
public:
 Tbase();
 virtual ~Tbase();
public:
 virtual Set()
 {
  Buffer[999]='c';
 }
 virtual void SetExample(Tbase* p)
 {
  p->Set();
 }
private:
 char Buffer[1000];
};

 

class FromTbase:public Tbase
{
public:
 FromTbase();
 ~FromTbase();
 virtual Set()
 {
  i=20;
  Tbase::Set();
 }
public:
 int i;
};

 

Tbase::Tbase()
{}
Tbase::~Tbase(){}

 

FromTbase::FromTbase():Tbase()
{}

 

FromTbase::~FromTbase(){}

 

typedef std::map<int,FromTbase*> TMap;

 

int _tmain(int argc, _TCHAR* argv[])
{

 

 FromTbase from;
 from.SetExample(&from);

 

 return 0;

 

}
建议阅读: 重载、覆盖、多态与函数隐藏