13.STL-谓词

• 谓词

• 普通函数或者仿函数的返回值是bool类型，称为谓词
• 一元谓词

• 查找容器中大于20的数字 find_if

• 二元谓词

• 对容器进行排序 sort

• lambda表达式 {}

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

//一元谓词
class GreaterThan20
{
public:
	bool operator()(int val)
	{
		return val > 20;
	}
};

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);


	vector<int>::iterator ret = find_if(v.begin(), v.end(), GreaterThan20());
	if ( ret != v.end())
	{
		cout << "找到大于20的数字为： " << *ret << endl;
	}
	else
	{
		cout << "未找到" << endl;
	}


}


//二元谓词
void myPrintInt( int val)
{
	cout << val << " ";
}

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

void test02()
{
	vector<int>v;

	v.push_back(10);
	v.push_back(30);
	v.push_back(20);
	v.push_back(40);
	v.push_back(50);

	sort(v.begin(), v.end()); //从小到大

	for_each(v.begin(), v.end(), myPrintInt);
	cout << endl;


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

	//lambda表达式  匿名函数  []代表lambda表达式标志  [](){}
	for_each(v.begin(), v.end(), [](int val){ cout << val << " "; });

	cout << endl;
}


int main(){
	//test01();
	test02();

	system("pause");
	return EXIT_SUCCESS;
}