函数对象

函数对象实质上是一个实现了operator()--括号操作符重载--的类

// c++_1.cpp : 定义控制台应用程序的入口点。
//

#include "stdafx.h"
#include <iostream>
#include <vector>
#include <algorithm>
#include <string>


using namespace std;


//累加器
template <typename T>
class Accumulater
{
private:
	int *_count;
	T  *_total;

public:
	Accumulater(int *count,  T *total)
	{
		_count = count;
		_total = total;
	}

	void operator()(T i)
	{
		(*_count)++;
		(*_total) += i;
	}
};


int _tmain(int argc, _TCHAR* argv[])
{
	vector<int> record1;
	for (int i = 0; i < 100; i++)
	{
		record1.push_back(i + 1);
	}

	int count = 0;
	int total = 0;

	Accumulater<int> sum(&count, &total);
	for_each(record1.begin(), record1.end(), sum);
    
	cout << "统计了" << count <<"个数，总和为： " <<total<<endl;

	//数组
	int records2[100];
	for (int i = 0; i < 100; ++i)
	{
		records2[i] = i+1;
	}

	count = 0;
	total = 0;

	for_each(records2, records2 + 100, sum);
	cout << "统计了" << count <<"个数，总和为： " <<total<<endl;

	system("pause");
	return 0;
}

结果如下：

函数对象类必须重载operator（）函数，函数对象完全可以用函数来代替：

 

template <typename T>
void printRecord(T i)
{
	cout << i << " ";
}

原函数对象为：

template <typename T>
class RecordPrinter
{
public:
	void operator()(T i)
	{
		cout << i << " ";
	}

};

for_each(records.begin(), records.end(), RecordPrinter<double>());