STL中函数适配器

首先为什么要用函数适配器？

STL中的函数适配器分类：

（1）绑定适配器用法
将一个操作数绑定到给定值而将二元函数对象转换为一元函数对象。
bind2nd:将给定值绑定到二元函数对象的第二个实参；
bind1st:将给定值绑定到二元函数对象的第一个参数；
示例程序如下：

#include
#include
#include
#include

using namespace std;

int main()
{
	int intArr[] = { 30,90,10,40,70,50,20,80 };
	const int N = sizeof(intArr) / sizeof(int);
	vectora(intArr, intArr + N);
	vector::iterator p = find_if(a.begin(), a.end(), bind2nd(greater(), 40));
	if (p == a.end())
		cout << "no element greater than 40" << endl;
	else
		cout << "first element greater than 40 is:" << *p << endl;
	system("pause");
	return 0;
}

(2)指针函数适配器用法
对一般自定义的函数使用

#include
#include
#include
#include

using namespace std;

bool g(int x, int y)
{
	return x > y;
}


int main()
{
	int intArr[] = { 30,90,10,40,70,50,20,80 };
	const int N = sizeof(intArr) / sizeof(int);
	vector<int>a(intArr, intArr + N);
	vector<int>::iterator p = find_if(a.begin(), a.end(), bind2nd(ptr_fun(g), 40));
	if (p == a.end())
		cout << "no element greater than 40" << endl;
	else
		cout << "first element greater than 40 is:" << *p << endl;
	system("pause");
	return 0;
}

（3）组合适配器
not1（…）：生成一元函数的逻辑反
not2(…)：生成二元函数的逻辑反

#include
#include
#include
#include

using namespace std;

int main()
{
	int intArr[] = { 30,90,10,40,70,50,20,80 };
	const int N = sizeof(intArr) / sizeof(int);
	vector<int>a(intArr, intArr + N);
	vector<int>::iterator p = find_if(a.begin(), a.end(), not1(bind2nd(greater<int>(), 15)));
	if (p == a.end())
		cout << "no element is not greater than 15" << endl;
	else
		cout << "first element that is not greater than 15 is:" << *p << endl;
	
	system("pause");
	return 0;
}

#include
#include
#include
#include

using namespace std;

int main()
{
	int intArr[] = { 30,90,10,40,70,50,20,80 };
	const int N = sizeof(intArr) / sizeof(int);
	vector<int>a(intArr, intArr + N);
	vector<int>::iterator p = find_if(a.begin(), a.end(), bind2nd(not2(greater<int>()), 15));
	if (p == a.end())
		cout << "no element is not greater than 15" << endl;
	else
		cout << "first element that is not greater than 15 is:" << *p << endl;
	system("pause");
	return 0;
}

（4）成员函数适配器用法
mem_fun(…):使成员函数作为函数对象，传入对象指针；
mem_fun_ref(…):使成员函数作为函数对象，传入对象引用；

#include
#include
#include
#include

using namespace std;

struct Car
{
	int id;
	Car(int id)
	{
		this->id = id;
	}
	void display()const
	{
		cout << "car" << id << endl;
	}
};


int main()
{
	vector<Car *>pcars;
	vector<Car>cars;
	for (int i = 0; i < 5; i++)
		pcars.push_back(new Car(i));
	for (int i = 5; i < 10; i++)
		cars.push_back(Car(i));

	cout << "elements in pcars:" << endl;
	for_each(pcars.begin(), pcars.end(), mem_fun(&Car::display));
	cout << endl;

	cout << "elements in cars:" << endl;
	for_each(cars.begin(), cars.end(), mem_fun_ref(&Car::display));
	cout << endl;

	for (size_t i = 0; i < pcars.size(); ++i)
		delete pcars[i];

	system("pause");
	return 0;
}

本文是在贺利坚老师的视频课的内容的基础上做的总结，仅作为后续自我复习使用。