函数指针

#include <iostream>
#include <cstdlib>
using namespace std;

// 声明函数指针变量
int (*fn)(int) = NULL;

// 定义函数指针类型
typedef int (*Fn)(int);

int cal(int v){ 
    return v;
};

int max(int a, int b){
    return a > b ? a : b;
}

// 函数指针做为参数
void proc(int v, Fn f){
    cout << f(v) << endl;
};

// 函数指针作为函数返回值
int (* retFP(string fName))(int, int){
    // lambda 表达式作为函数指针返回
    int (*fp)(int,int) = [](int x, int y){ return x > y ? y : x;};
    // 返回一个全局函数
    if(fName == "max"){
        fp = max;
    }

    return fp;
}
// 或者下面的方式
typedef int (*RetFP)(int, int);
RetFP retFP(string fName){
    int (*fp)(int,int) = [](int x, int y){ return x > y ? y : x;};
    if(fName == "max"){
        fp = max;
    }
    return fp;
}


int main()
{
    fn = cal;
    cout << (*fn)(10) << endl;
    cout << fn(10) << endl;
    
    Fn f1 = cal;
    cout << (*f1)(20) << endl;

    proc(30, cal);

    auto myFP = retFP("max");
    cout << myFP(3, 6) << endl;
    
    return 0;
}

Start
10
10
20
30
0
Finish

struct type
{
    int i;
 
    type(): i(3) {}
 
    void f(int v) const
    {
        // this->i = v;                 // compile error: this is a pointer to const
        const_cast<type*>(this)->i = v; // OK as long as the type object isn't const
    }
};
 
int main() 
{
    type t; // if this was const type t, then t.f(4) would be undefined behavior
    t.f(4);
    std::cout << "type::i = " << t.i << '\n';       // type::i = 4

    void (type::*pmf)(int) const = &type::f; // pointer to member function
    (t.*pmf)(40);
    std::cout << "type::i = " << t.i << '\n';       // type::i = 40
}