举例1：普通函数指针：
int(*fun)(double, int);fun = [](double a, int b) {cout << a << endl;cout << b << endl;return 3;};int x = fun(34, 123);
typedef定义函数指针类型：
typedef int(*padd)(int, int, int);int add(int a, int b, int d){return a + b + d;}int mul(int a, int b, int d){return a * b * d;}int main(){padd p1 = add; //p1为padd类型的变量p1(1, 2, 3);padd p2 = mul; //p2为padd类型的变量p2(1, 2, 3);return 0;}
如果不使用typedef定义函数指针类型，则不能声明变量。
举例2：类成员函数指针
#include <iostream>using namespace std;class A {public:A() = default;int SayHello(int a){cout << a << endl;return 100;}};typedef int(A::*FP)(int); //类成员函数指针，要加一个类的作用域，四饼运算符，哈哈哈int main(){FP fp = &A::SayHello;A a;int x = (a.*fp)(3); //*fp可以称为解引用，取得函数名字(a.*fp)cout << x << endl;return 0;}
再举个例子：
假设我们有一个类Person，其中有一个成员函数void sayHello()，我们可以使用类成员函数指针来实现回调机制：
#include <iostream>class Person {public:void sayHello() {std::cout << "Hello, I'm a person!" << std::endl;}};void callback(void (Person::*func)(), Person* p) {(p->*func)();}int main() {Person p;callback(&Person::sayHello, &p);return 0;}
在这个例子中，callback函数接受一个类成员函数指针和一个Person对象的指针作为参数，当函数被调用时，它会使用指针调用Person对象的成员函数。
通过这种方式，我们可以将一个成员函数作为参数传递给另一个函数，从而实现回调机制，这在事件处理和异步编程中非常常见。
typedef的作用，定义一个新的类型：
class Foo {public:float bar(int x) {return x * 3.14f; }};typedef float (Foo::*BarPtr)(int);
In this case, BarPtr is now a type that can hold a pointer to the bar member function of Foo.
这里的BarPtr就是新的类型，可以用来接收类的成员函数指针。
https://blog.molecular-//09/19/generic-type-safe-delegates-and-events-in-c/
https://skypjack.github.io/-01-25-delegate-revised/
/Articles/7150/Member-Function-Pointers-and-the-Fastest-Possible
/docs/en/zos/2.3.0?topic=only-explicit-specialization-c
//11/20/c-delegates/
#include <iostream>#include <cstring>#include <vector>using namespace std;template<typename T>void f(T&& t){if (std::is_same<int, T>::value) //T&&{cout << "int" << endl;}if (std::is_same<int&, T>::value) //T&&{cout << "int&" << endl;}if (std::is_same<int&&, T>::value) //T&&{cout << "int&&" << endl;}}template<typename T>T sum(T t){return t;}template<typename T, typename ... Types>T sum(T first, Types ... rest){int count = sizeof...(rest);return first + sum<T>(rest...);}//template <class... T>//void f2(T... args)//{//cout << sizeof...(args) << endl; //打印变参的个数//}template <typename...> class Foo;template <typename A, typename B>class Foo<A, B>{public:void output() {std::cout << a_ << b_ << '\n';}A a_;B b_;};template <typename A, typename B, typename C>class Foo<A, B, C>{public:void output() {std::cout << a_ << b_ << c_ << '\n';}A a_;B b_;C c_;};template<typename>class FF;template<typename T, typename ...B>class FF<T(B...)> {public:void Show(){int count = sizeof...(B);}int a;};using xxx = FF<int(int, int, int)>;xxx ddd{};template <typename> class Foo2;template <typename A, typename B>class Foo2<void(A, B)> {};template <typename A, typename B, typename C>class Foo2<void(A, B, C)> {};#define DefineX(name) cout<<23.name<<endl;void call(int a){std::cout << "hello" << endl;}void my_func(int) {/* ... */ }struct my_class {void my_member(int) {/* ... */ }};class Student{public:void SayHello(int b){cout << "hello" << endl;}};typedef void(*FunctionPointer)(int);typedef void (Student::*FunctionPointer2)(int);void nihao(int a){int bb = a + 1;}using proto_fn_type = int(string, int&&...);proto_fn_type* _caller;int main(){_caller = [](string a, int&&...)->int {string b = a;cout << "hello" << endl;return 321;};int xdd = _caller("hello", 2);FunctionPointer p = nihao;p(3);Student s;FunctionPointer2 p2 = &(Student::SayHello);(s.*p2)(3);FF<int(int, int)> aaa{aaa.a = 3};Foo2<void(int, int)> f2{};Foo2<void(int, int, std::string)> f3;Foo<int, int> aa{aa.a_ = 3,aa.b_ = 4,};int(*fun)(double, int);fun = [](double a, int b) {cout << a << endl;cout << b << endl;return 12;};int x = fun(34, 123);std::cin.get();return 0;}
函数指针延伸，委托类：
#include <iostream>#include <iomanip>#include <string>#include "Test.h"using namespace std;template<typename>class XDelegate;template<typename Ret, typename ...Args>class XDelegate<Ret(Args...)>{using proto_fn_type = Ret(void*);public:Ret operator()(){return _caller(_this);}template<auto method, typename Type>void connect(Type* instance) noexcept{_this = instance;_caller = [](void* data)->Ret{Type* payload = static_cast<Type*>(data);return Ret(std::invoke(method, payload));};}private:proto_fn_type* _caller;void* _this;};int f(int* a){return *a;}int main(){XDelegate<int(int)> b{};int p = 12345;b.connect<&f, int>(&p);int a = b();return 0;}
