c++中STL怎样编写自己的函数对象

#include <iostream>
#include <functional>
#include <algorithm>
using namespace std;

template <class Arg, class Result>
class  is_odd  
{
public:

typedef Arg argument_type;
typedef Result res;
bool operator() ( const int& value)const {return (value%2==1); }
};


int main () {
  int values[] = {1,2,3,4,5};
  int cx;
  cx = count_if ( values, values+5, not1(is_odd<int,bool>()) );
  cout << "There are " << cx << " elements with even values.\n";
  return 0;

}

方法二：继承 函数对象

#include <iostream>#include <functional>using namespace std;struct IsOdd : public unary_function<int,bool> {  bool operator() (int number) {return (number%2==1);}};int main () {  IsOdd IsOdd_object;  IsOdd::argument_type input;  IsOdd::result_type result;  cout << "Please enter a number: ";  cin >> input;  result = IsOdd_object (input);  cout << "Number " << input << " is " << (result?"odd":"even") << ".\n";  return 0;}