它使得以统一的方式绑定成员变量和函数成为可能。下面是Car类的示例。更常见的用法是绑定std::pair::first和::second，当在STL算法和Boost上使用时。

#include <list>
#include <algorithm>
#include <iostream>
#include <iterator>
#include <boost/lambda/lambda.hpp>
#include <boost/lambda/bind.hpp>


class Car {
public:
    Car(int s): speed(s) {}
    void drive() {
        std::cout << "Driving at " << speed << " km/h" << std::endl;
    }
    int speed;
};

int main() {

    using namespace std;
    using namespace boost::lambda;

    list<Car> l;
    l.push_back(Car(10));
    l.push_back(Car(140));
    l.push_back(Car(130));
    l.push_back(Car(60));

    // Speeding cars
    list<Car> s;

    // Binding a value to a member variable.
    // Find all cars with speed over 60 km/h.
    remove_copy_if(l.begin(), l.end(),
                   back_inserter(s),
                   bind(&Car::speed, _1) <= 60);

    // Binding a value to a member function.
    // Call a function on each car.
    for_each(s.begin(), s.end(), bind(&Car::drive, _1));

    return 0;
}

指向成员的指针是c++的类型安全等价于C的offsetof()，它在stddef.h中定义:两者都返回某个字段位于类或结构中的信息。虽然在c++中也可以将offset()用于某些足够简单的类，但在一般情况下，它会失败，尤其是虚拟基类。因此指针成员被添加到标准中。它们还提供了更简单的语法来引用实际字段:

struct C { int a; int b; } c;
int C::* intptr = &C::a;       // or &C::b, depending on the field wanted
c.*intptr += 1;

要比:

struct C { int a; int b; } c;
int intoffset = offsetof(struct C, a);
* (int *) (((char *) (void *) &c) + intoffset) += 1;

至于为什么要使用offsetof()(或指向成员的指针)，在stackoverflow的其他地方有很好的答案。这里有一个例子:宏的C偏移是如何工作的?

IBM有更多关于如何使用它的文档。简单地说，您使用指针作为类的偏移量。你不能在它们所指向的类之外使用这些指针，所以:

  int Car::*pSpeed = &Car::speed;
  Car mycar;
  mycar.*pSpeed = 65;

It seems a little obscure, but one possible application is if you're trying to write code for deserializing generic data into many different object types, and your code needs to handle object types that it knows absolutely nothing about (for example, your code is in a library, and the objects into which you deserialize were created by a user of your library). The member pointers give you a generic, semi-legible way of referring to the individual data member offsets, without having to resort to typeless void * tricks the way you might for C structs.

我喜欢*和&运算符:

struct X 
{ 
    int a {0}; 
    int *ptr {NULL};

    int &fa() { return a; }
    int *&fptr() { return ptr; }
};

int main(void) 
{
    X x;
    int X::*p1 = &X::a;     // pointer-to-member 'int X::a'. Type of p1 = 'int X::*'
    x.*p1 = 10;

    int *X::*p2 = &X::ptr;  // pointer-to-member-pointer 'int *X::ptr'. Type of p2 = 'int *X::*' 
    x.*p2 = nullptr;
    X *xx;
    xx->*p2 = nullptr;

    int& (X::*p3)() = X::fa; // pointer-to-member-function 'X::fa'. Type of p3 = 'int &(X::*)()'
    (x.*p3)() = 20; 
    (xx->*p3)() = 30;

    int *&(X::*p4)() = X::fptr;  // pointer-to-member-function 'X::fptr'. Type of p4 = 'int *&(X::*)()'
    (x.*p4)() = nullptr; 
    (xx->*p4)() = nullptr;
}

事实上，只要成员是公共的或静态的，所有都是真的

你以后可以在任何实例上访问这个成员:

int main()
{    
  int Car::*pSpeed = &Car::speed;    
  Car myCar;
  Car yourCar;

  int mySpeed = myCar.*pSpeed;
  int yourSpeed = yourCar.*pSpeed;

  assert(mySpeed > yourSpeed); // ;-)

  return 0;
}

请注意，您确实需要一个实例来调用它，因此它不像委托那样工作。 它很少被使用，我这么多年来可能用过一两次。

通常使用接口(即c++中的纯基类)是更好的设计选择。

它使得以统一的方式绑定成员变量和函数成为可能。下面是Car类的示例。更常见的用法是绑定std::pair::first和::second，当在STL算法和Boost上使用时。

#include <list>
#include <algorithm>
#include <iostream>
#include <iterator>
#include <boost/lambda/lambda.hpp>
#include <boost/lambda/bind.hpp>


class Car {
public:
    Car(int s): speed(s) {}
    void drive() {
        std::cout << "Driving at " << speed << " km/h" << std::endl;
    }
    int speed;
};

int main() {

    using namespace std;
    using namespace boost::lambda;

    list<Car> l;
    l.push_back(Car(10));
    l.push_back(Car(140));
    l.push_back(Car(130));
    l.push_back(Car(60));

    // Speeding cars
    list<Car> s;

    // Binding a value to a member variable.
    // Find all cars with speed over 60 km/h.
    remove_copy_if(l.begin(), l.end(),
                   back_inserter(s),
                   bind(&Car::speed, _1) <= 60);

    // Binding a value to a member function.
    // Call a function on each car.
    for_each(s.begin(), s.end(), bind(&Car::drive, _1));

    return 0;
}