[C++知识库]C++STL（六）

谓词

谓词是指昔通函数或重载的operator(拨回值是bool类型的函数对象(仿函数)。如果operator接受一个参数，那么叫做一元谓词,如果接受两个参数，那么叫做二元谓词，谓词可作为一个判断式。

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

class MoreThan20 
{
public:
	bool operator()(int val)
	{
		return val > 20;
	}
};

//一元谓词
void test01()
{
	vector<int>v;
	v.push_back(10);
	v.push_back(20);
	v.push_back(30);
	v.push_back(40);
	v.push_back(50);

	//查找第一个大于20的数字
	//vector<int>::iterator it = find_if(v.begin(),v.end(),MoreThan20());
	auto it = find_if(v.begin(), v.end(), MoreThan20());
	cout << *it << endl;
}


class MyCompare 
{
public:
	bool operator()(int v1,int v2)
	{
		return v1 > v2;
	}
};

//二元谓词
void test02()
{
	vector<int>v;
	v.push_back(10);
	v.push_back(20);
	v.push_back(30);
	v.push_back(40);
	v.push_back(50);

	sort(v.begin(),v.end(),MyCompare());

	for (auto it = v.begin();it != v.end();it++)
	{
		cout << *it << " ";
	}
	cout << endl;
}

int main()
{
	test02();
	return 0;
}

?内建函数对象

STL内建了一些函数对象。分为:算数类函数对象,关系运算类函数对象，逻辑运算类仿函数。这些仿函数所产生的对象，用法和一般函数完全相同，当然我们还可以产生无名的临时对象来履行函数功能。使用内建函数对象，需要引入头文件#include<functional>。

#include <iostream>
#include <vector>
using namespace std;
//内建函数头文件
#include <functional>
#include <algorithm>

//算术类函数对象
void test01()
{
	//template<class T> T negate<T> //取反仿函数
	negate<int>n;
	cout << n(10) << endl;

	//加法仿函数
	plus<int>p;
	cout << p(1,1) << endl;
}

//关系运算类函数对象
void test02()
{
	vector<int>v;
	v.push_back(10);
	v.push_back(20);
	v.push_back(30);
	v.push_back(40);
	v.push_back(50);

	//内建函数大于
	sort(v.begin(),v.end(),greater<int>());

	/*for (auto it = v.begin();it != v.end();it++)
	{
		cout << *it << " ";
	}
	cout << endl;*/

	for_each(v.begin(), v.end(), [](int val) {cout << val << " "; });
}

int main()
{
	test02();
	return 0;
}

?适配器使用

#include <iostream>
#include <algorithm>
#include <vector>
#include <functional>
#include <string>
using namespace std;
 
class MyPrint:public binary_function<int,int,void>
{
public:
	void operator()(int v,int start) const
	{
		cout << v + start<< " ";
	}
};

//绑定适配器
void test01()
{
	vector<int>v;
	for (int i = 0;i<10;i++)
	{
		v.push_back(i);
	}

	//for_each(v.begin(), v.end(), [](int val) {cout << val << " "; });
	int num;
	cin >> num;
	for_each(v.begin(), v.end(),bind2nd(MyPrint(),num));
}

class MoreThanFive : public unary_function<int,bool>
{
public:
	bool operator()(int val) const
	{
		return val > 5;
	}
};

//一元取反适配器 not1
void test02()
{
	//一元取反
	vector<int>v;
	for (int i = 0; i < 10; i++)
	{
		v.push_back(i);
	}

	//查找大于5的数字
	auto pos = find_if(v.begin(), v.end(), not1(MoreThanFive()));
	cout << *pos << endl;
}

void MyPrint03(int v,int start)
{
	cout << v + start << " ";
}

//函数指针适配器
void test03()
{
	vector<int>v;
	for (int i = 0; i < 10; i++)
	{
		v.push_back(i);
	}

	//for_each(v.begin(), v.end(), MyPrint03);
	for_each(v.begin(), v.end(), bind2nd(ptr_fun(MyPrint03),100));
}

//成员函数适配器
class Person 
{
public:
	string m_Name;
	int m_Age;
public:
	Person(string name,int age):m_Name(name),m_Age(age){}
	void showPerson()
	{
		cout << "成员函数中:姓名：" << m_Name << "年龄：" << m_Age << endl;
	}
};

void MyPrintPerson(Person &p)
{
	cout << "姓名：" << p.m_Name << " " << "年龄：" << p.m_Age << endl;
}

void test04()
{
	vector<Person>v;

	Person p1("aaa", 10);
	Person p2("bbb", 15);
	Person p3("ccc", 13);
	Person p4("ddd", 19);

	v.push_back(p1);
	v.push_back(p2);
	v.push_back(p3);
	v.push_back(p4);
	
	//for_each(v.begin(), v.end(), MyPrintPerson);
	//成员函数适配器
	for_each(v.begin(), v.end(),mem_fun_ref(&Person::showPerson));
}

int main()
{
	test04();
	return 0;
}