如何声明和使用指向类数据成员的指针?

[liufangbj]

如题
谢谢啦~~

[clhposs]

class some;

some *p;

[liufangbj]

不是指向类，而是指向类的数据成员. 如下类，声明指针指向a或者b 并使用该指针

class some 
{
  int a;
  int b;
 some()
  {
   a=0;
   b=0;
   }
}

[liufangbj]

没有人回,自己先顶一下,大家多帮忙啊!!!

[simo110]

using some::a;
int *pa = a;

[simo110]

成员函数就要用函数指针
函数指针还有些特别

[taodm]

你就不能找本好点的C++教材翻一翻么？
这是一个基本语法呀。

[SenerityChzr]

class some {
public:
some() { a=0; b=0; }

int a; int b;
}

int some::*piA = NULL; // 声明some的类的成员变量指针，可以指向其任何一个int型public成员变量，


但这样做是不符合C++面向对象理念的……

[liufangbj]

我不明白如下程序的输出:

Exapmle.h

#ifndef EXAMPLE_H_
#define EXAMPLE_H_

class Example
{
	private:
		int feet;
		int inches;
	public:
		Example();
		Example(int ft);
		~Example();
		void show_in() const;
		void show_ft() const;
		void use_ptr() const;
};

#endif /*EXAMPLE_H_*/

Exapmle.cpp

#include <iostream.h>
#include "Example.h"

Example::Example()
{
	feet   = 0;
	inches = 0;
}

Example::Example(int ft)
{
	feet   = ft;
	inches = 12*ft;
}

Example::~Example()
{
	
}

void Example::show_in() const
{
	cout<< inches<<"  inches\n";
}

void Example::show_ft() const
{
	cout<< feet<<"  feet\n";
}

void Example::use_ptr() const
{
	cout<<"3333333333333333333333333333333333333333335555555555555555555555555555555555555555555555555\n";
	Example yard(3);
	
	 yard.show_ft();
	 yard.show_in();
	int Example::*pt;
	pt = &Example::inches;
	cout<<"Set pt to &Example::inches:\n";
	cout<<"this->pt:"<<this->*pt<<endl;
	cout<<"yard.*pt:"<<yard.*pt<<endl;
	pt =&Example::feet;
	cout<<"Set pt to &Example::feet:\n";
	cout<<"this->pt:"<<this->*pt<<endl;
	cout<<"yard.*pt:"<<yard.*pt<<endl;
	
	
	void (Example::*pf)() const;
	pf = &Example::show_in;
	cout<<"Set pf to &Example::show_in:\n";
	cout<<"Using(this->pf):";
	(this->*pf)();
	cout<<"Using(yard.*pf)():";
	(yard.*pf)();		
}

主函数

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

int main() {
	Example car(15);
	Example van(20);
	Example garage;
	cout<<0xabcd<<endl;
	cout<<0xcdab<<endl;
	
	cout<<"car.use_ptr() output:\n";
	car.use_ptr();
	cout<<"\nvan.use_ptr() output:\n";
	van.use_ptr();
	return 0;
}

[liufangbj]

输出结果:

43981
52651
car.use_ptr() output:

3  feet
36  inches
Set pt to &Example::inches:
this->pt:180
yard.*pt:36
Set pt to &Example::feet:
this->pt:15
yard.*pt:3
Set pf to &Example::show_in:
Using(this->pf):180  inches
Using(yard.*pf)():36  inches

van.use_ptr() output:
3  feet
36  inches
Set pt to &Example::inches:
this->pt:240
yard.*pt:36
Set pt to &Example::feet:
this->pt:20
yard.*pt:3
Set pf to &Example::show_in:
Using(this->pf):240  inches
Using(yard.*pf)():36  inches

[yuzl32]

#include <iostream>

using namespace std;

class MyClass
{
public:
	int m_Id;	
};

int main(void)
{		
	int MyClass::*pId;
	MyClass c;
	//指向成员的指针
	pId = &MyClass::m_Id;
	
	//偏移方式获取m_Id的地址并赋值
	c.*pId = 5;
	
	cout << c.m_Id ;
	
	return 0;
}

/out:Client.exe
Client.obj

E:\>Client
5

[axing0308008341]

你得先有指向类对象的指针,才能指得到他的数据成员吧~

[yuzl32]

void Example::use_ptr() const
{
    cout<<"3333333333333333333333333333333333333333335555555555555555555555555555555555555555555555555\n";
    Example yard(3);
    
     yard.show_ft();
     yard.show_in();
    int Example::*pt;          //声明一个指向类成员的指针,它以偏移量的方式存在
    pt = &Example::inches;     //将成员inches的偏移量赋值给pt
    cout<<"Set pt to &Example::inches:\n";
    cout<<"this->pt:"<<this->*pt<<endl;    //this是指针,*pt为偏移量,this->*pt相当于this->inches
    cout<<"yard.*pt:"<<yard.*pt<<endl;     //yard是对象,*pt为偏移量,yard->*pt相当于yard.inches
    pt =&Example::feet;        //同上分析，以下雷同
    cout<<"Set pt to &Example::feet:\n";
    cout<<"this->pt:"<<this->*pt<<endl;
    cout<<"yard.*pt:"<<yard.*pt<<endl;
    
    
    void (Example::*pf)() const;
    pf = &Example::show_in;
    cout<<"Set pf to &Example::show_in:\n";
    cout<<"Using(this->pf):";
    (this->*pf)();
    cout<<"Using(yard.*pf)():";
    (yard.*pf)();        
}

[yuzl32]

void Example::use_ptr() const
{
    cout<<"3333333333333333333333333333333333333333335555555555555555555555555555555555555555555555555\n";
    Example yard(3);
    
     yard.show_ft();
     yard.show_in();
    int Example::*pt;          //声明一个指向类成员的指针,它以偏移量的方式存在
    pt = &Example::inches;     //将成员inches的偏移量赋值给pt
    cout<<"Set pt to &Example::inches:\n";
    cout<<"this->pt:"<<this->*pt<<endl;    //this是指针,*pt为偏移量,this->*pt相当于this->inches
    cout<<"yard.*pt:"<<yard.*pt<<endl;     //yard是对象,*pt为偏移量,yard.*pt相当于yard.inches
    pt =&Example::feet;        //同上分析，以下雷同
    cout<<"Set pt to &Example::feet:\n";
    cout<<"this->pt:"<<this->*pt<<endl;
    cout<<"yard.*pt:"<<yard.*pt<<endl;
    
    
    void (Example::*pf)() const;
    pf = &Example::show_in;
    cout<<"Set pf to &Example::show_in:\n";
    cout<<"Using(this->pf):";
    (this->*pf)();
    cout<<"Using(yard.*pf)():";
    (yard.*pf)();        
}

[liufangbj]

谢谢楼上的
^^