operator()

https://blog.csdn.net/infoworld/article/details/38901127

1、表达式格式

HWND operator ()() const throw()
{
    return m_hWnd;
}

View Code

与类型改变表达式格式区别：

operator HWND() const throw()
    {
        return m_hWnd;
    }

案例：

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

 class Total
{
public:
    Total(float sum,float discount)
    {
        sum_ = sum;
        discount_ = discount;
    }
    ~Total(){}
     operator float()
    {
        return sum_* discount_;
    }
     operator std::string()
    {
        char str[128];
        sprintf(str,"%f",sum_* discount_);
        return std::string(str);
    }
     float operator()()
    {
        return sum_* discount_;
    }
    float sum_;
    float discount_;
};

int main(int argc, char const *argv[])
{
    Total to(89,0.8);
    cout << to << endl;
    cout << to() << endl;
    cout << (std::string)to << endl;
    //cout << to(0.9) << endl;
    return 0;
}

2、调用方式：两种

先声明；再实例化；再调用，用对象调用operator()；

#include <iostream>
using namespace std;

template<typename T>
struct m_plus
{
    T operator()(const T& x, const T& y) { return x + y; }
};

int main(int argc, char *argv[])
{
    // 定义其对象  调用其operator()
    m_plus<int> op;
    cout << op(1, 2) << endl;
    // 产生一个匿名对象  这是仿函数的主流用法
    cout << m_plus<int>()(1, 2) << endl;
    return 0;
}