函数运算符（）重载

函数运算符()也能重载，它使得对象看上去像是一个函数名

ReturnType operator() (Parameters)

{

......

}

ClassName Obj;

Obj(real_parameters);

//->obj.operator() (real_parameters);

#include 
     
      using namespace std;class Test{public:    int operator() (int a, int b)    {        cout << "operator() called." << a << " " << b << endl;        return a + b;    }};int main(){    Test sum;    int s = sum(3, 4);//sum对象看上去像是一个函数，故也成为“函数对象”    cout << "a + b = " << s << endl;    return 0;}
     

 

#include 
     
      using namespace std;class Less{    int thres_;public:    Less(int th) :thres_(th) {}    bool operator() (int);};bool Less::operator() (int value){    return (value < thres_);}void Filter(int *array, int num, Less fn){    for (int i = 0; i < num; i++)    {        if (fn(array[i]))            cout << array[i] << " ";    }    cout << endl;}int main(){    int array[5] = { 1,-4,10,0,-1 };    int thres;    cout << "thres:";    cin >> thres;    Less less_than(thres);    Filter(array, 5, less_than);    return 0;}