[C++STL]仿函数用法介绍

Posted 2021-06-27 Wecccccccc

代码如下:

#include <iostream>
#include <string>
using namespace std;

//函数对象在使用时，可以像普通函数那样调用，可以有参数，可以有返回值
class MyAdd
{
public:
	int operator()(int a, int b)
	{
		return a + b;
	}
};

void test01()
{
	MyAdd myAdd;
	cout << myAdd(10, 10) << endl;
}

//函数对象可以有自己的状态
class MyPrint
{
public:
	MyPrint()
	{
		count = 0;
	}

	void operator()(string test)
	{
		cout << test << endl;
		count++;
	}

	int count = 0;
};

void test02()
{
	MyPrint myPrint;
	myPrint("hello world");
	myPrint("hello world");
	myPrint("hello world");

	cout << "count = " << myPrint.count << endl;

}

//函数对象可以作为参数传递
void doPrint(MyPrint &mp, string test)
{
	mp(test);
}

void test03()
{
	MyPrint myPrint;
	doPrint(myPrint, "hello c++");
}

int main()
{
	test01();
	test02();
	test03();
	return 0;
}

测试结果:

总结:

一元谓词
代码如下:

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

struct GreaterFive {
	bool operator()(int a)
	{
		return a > 5;
	}
};

void test01()
{
	vector<int>v;
	for (int i = 0; i < 10; i++)
	{
		v.push_back(i);
	}
	vector<int>::iterator it = find_if(v.begin(), v.end(), GreaterFive());
	if (it == v.end())
	{
		cout << "no find" << endl;
	}
	else
	{
		cout << "find" << *it << endl;
	}

}

int main()
{
	test01();
	return 0;
}

测试结果:

总结:

二元谓词
代码如下:

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

class cmp
{
public:
	bool operator()(int a, int b)
	{
		return a > b;
	}
};

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

	sort(v.begin(), v.end());
	for (vector<int>::iterator it = v.begin(); it != v.end(); it++)
	{
		cout << *it << " ";
	}
	cout << endl;
	cout << "---------------------------------------" << endl;
	sort(v.begin(), v.end(), cmp());
	for (vector<int>::iterator it = v.begin(); it != v.end(); it++)
	{
		cout << *it << " ";
	}
	cout << endl;

}

int main() {
	test01();
	return 0;
}

测试结果:

总结:

代码如下:

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

void test01()
{
	negate<int> n;
	cout << n(50) << endl;
}

void test02()
{
	plus<int>p;
	cout << p(10, 20) << endl;
}

int main()
{
	test01();
	test02();
	return 0;
}

测试结果:

总结:

代码如下:

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

class cmp
{
public:
	bool operator()(int a, int b)
	{
		return a > b;
	}
};

void test01()
{
	vector<int>v;
	v.push_back(10);
	v.push_back(20);
	v.push_back(50);
	v.push_back(40);
	v.push_back(90);
	v.push_back(70);

	for (vector<int>::iterator it = v.begin(); it != v.end(); it++)
	{
		cout << *it << " ";
	}
	cout << endl;

	sort(v.begin(), v.end(), greater<int>());
	for (vector<int>::iterator it = v.begin(); it != v.end(); it++)
	{
		cout << *it << " ";
	}
	cout << endl;

}

int main()
{
	test01();
	return 0;
}

测试结果:

总结:

代码如下:

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

void test01()
{
	vector<bool> v;
	v.push_back(true);
	v.push_back(false);
	v.push_back(true);
	v.push_back(false);

	for (vector<bool>::iterator it = v.begin(); it != v.end(); it++)
	{
		cout << *it << " ";
	}
	cout << endl;

	vector<bool> v2;
	v2.resize(v.size());
	transform(v.begin(), v.end(), v2.begin(), logical_not<bool>());
	for (vector<bool>::iterator it = v2.begin(); it != v2.end(); it++)
	{
		cout << *it << " ";
	}
	cout << endl;

}

int main()
{
	test01();
	return 0;
}

测试结果:

总结: