Thinking in C++: Pointers to members 指向成员的指针

通常来说，一个指针（pointer）是一个存储地址的变量，你能在运行时去改变它，并且指针可以指向数据或函数。

但在C++中，指向成员的指针（pointer-to-member）指向的是class或struct中的成员，但在class中并没有地址，所以指向成员的指针实际上是存储的偏移量（offset），你不能生成一个实际的地址直到你将某个特殊的对象的起始地址（starting address）与这个偏移量结合起来。

//: C11:PointerToMemberData.cpp
#include <iostream>
using namespace std;
class Data {
public:
	int a, b, c;
	void print() const {
		cout << "a = " << a << ", b = " << b
		<< ", c = " << c << endl;
	}
};
int main() {
	Data d, *dp = &d;
	int Data::*pmInt = &Data::a;
	dp->*pmInt = 47;
	pmInt = &Data::b;
	d.*pmInt = 48;
	pmInt = &Data::c;
	dp->*pmInt = 49;
	dp->print();
} ///:~

上面的例子是指向成员变量的指针，下面展示指向成员函数的指针：

//: C11:PointerToMemberFunction.cpp
#include <iostream>
using namespace std;
class Widget {
public:
void f(int) const { cout << "Widget::f()\n"; }
void g(int) const { cout << "Widget::g()\n"; }
void h(int) const { cout << "Widget::h()\n"; }
void i(int) const { cout << "Widget::i()\n"; }
};
int main() {
Widget w;
Widget* wp = &w;
void (Widget::*pmem)(int) const = &Widget::h;
(w.*pmem)(1);
(wp->*pmem)(2);
} ///:~

指向静态成员的指针，声明的方式和普通指针是一样的，但跟指向普通成员的指针不一样，不需要class的限定，只是赋值的时候，还得加上类的限定符。

class A
{
    static int _val;
    static int val();
};

int *p_val = &A::_val;
int (*p_func) = &A::val;

下面是一个结合本书和msdn上一个例子的代码：

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

class Data{
public:
	static int a;
public:
	int b,c;
	void print() const{
		cout<<"a="<<a<<",b="<<b<<",c="<<c<<endl;
	}
};

int Data::a = 10;
int *p = &Data::a; //static member pointer
int Data::*p2 = &Data::b; //member pointer
int Data::*p3 = &Data::c; //member pointer

class Window
{
public:
	Window();
	Window(int x1,int y1, int x2, int y2);
	bool SetCaption(const char *szTitle);
	const char *GetCaption();
	char *szWinCaption;
};

//pointer to data member
char * Window::pwCaption = &Window::szWinCaption;
//pointer to function member
const char *(Window::*pfnGetCaption)()=&Window::GetCaption;
bool (Window::*pfnSetCaption)(const char *) = &Window::SetCaption;

int main(int argc, char* argv[])
{
	Data ddd;
	ddd.print();
	*p = 40;
	ddd.*p2 = 50;
	ddd.*p3 = 60;
	ddd.print();


	int tt;
	cin>>tt;

}