类里面的成员函数指针使用

先看代码

#include <iostream>using namespace std;typedef void (*func)(); //含简单的定义一个函数指针，很容易用这个方法来实现指令，用作各种handler等等void print(){        cout << "print" <<endl;}class A{        typedef void (A::*classfunp)()；//指明这个函数指针是指向类A的，不能指向其他类的函数        public:                classfunp g;                void print()                {                        cout << "A::print" << endl;                }                void h()                {                        g = &A::print;  // 将函数print在A中的地址赋给函数指针g。使用&this->print报错为forbids taking the address of a bound memeber function to from a pointer to memeber function,意思就是不能将一个成员函数的地址当成一个指向成员函数的指针，下面解释，为什么                        (this->*g)();  //去掉this不对，因为g并不是A的一个成员变量，报错为：must use .* or->* to call point-to-member function                }                };int main(){        A a;  a.h();  returnr 0;}----->A::print;

 要知道为什么不能用this->print，请看

4.2Array-to-pointer conversion [conv.array]
1An lvalue or rvalue of type “array ofN T” or “array of unknownbound of T” can be converted to an rvalue
oftype “pointer to T.” The result is a pointer to the first elementof the array.
2 A string literal(2.13.4) that is not a wide string literal can be converted to anrvalue of type “pointer to
char”; awide string literal can be converted to an rvalue of type “pointerto wchar_t”. In either case,
theresult is a pointer to the first element of the array. Thisconversion is considered only when there is an
explicitappropriate pointer target type, and not when there is a general needto convert from an lvalue to an
rvalue.[Note: this conversion is deprecated. See Annex D. ] For the purposeof ranking in overload resolution
(13.3.3.1.1),this conversion is considered an array-to-pointer conversion followedby a qualification
conversion (4.4).[Example: "abc" is converted to “pointer to const char”as an array-to-pointer conversion,
andthen to “pointer to char” as a qualification conversion. ]
4.3Function-to-pointer conversion [conv.func]
1An lvalue of function type T can be converted to an rvalue of type“pointer to T.” The result is a pointer to
thefunction.50)
2 [Note: See 13.4 foradditional rules for the case where the function is overloaded.]

从上面我们知道为什么不能直接使用一个对象的函数地址了，因为重载，例如

一个类里面有函数f(),f(int)，当我们使用this->f时，到底使用的是要哪个f的地址呢，除非我们传入参数进去

通过下面的例子就知道了
typedef void (*func)();void f();void f(int);func p = f;p();p(1);//错误，因为函数指针p是指向f()的而不是f(1)

通过使用函数指针，我们可以制作各种handler，用这些handler为我们做不同的事，如信号的一个函数

signal(intsigno, int (*handler)());

在游戏里面编写各种gm指令；做一些框架，为通用功能的特殊部分编写自己的接口，通过函数指着指向他们等等