18.2.2【STL常用查找算法find_if】

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


/*
    5.2.2 find_if
        按条件查找元素
        find_if(iterator beg, iterator end, _Pred);
        // 按值查找元素，找到返回指定位置迭代器，找不到返回结束迭代器位置
        // beg 开始迭代器
        // end 结束迭代器
        // _Pred 函数或者谓词（返回bool类型的仿函数）
        find_if按条件查找使查找更加灵活，提供的仿函数可以改变不同的策略
*/


class Greater5
{
public:
    bool operator()(int val) //谓词
    {
        return val > 5;
    }
};


void test522() //查找内置数据类型
{
    vector<int> v;
    for(int i=0; i<10; i++)
    {
        v.push_back(i+1);
    }

    vector<int>::iterator it = find_if(v.begin(), v.end(), Greater5());
    if(it == v.end())
    {
        cout << "未找到" << endl;
    }
    else
    {
        cout << "找到了：" << *it << endl;
    }
}


class Person
{
public:
    string name;
    int age;

public:
    Person(string _name, int _age)
    {
        this->name = _name;
        this->age = _age;
    }
};


class Greater20
{
public:
    bool operator()(Person & p) //谓词
    {
        return p.age > 20;
    }
};


void test522_2() //查找自定义数据类型
{
    vector<Person> v;
    Person p1("aaa", 10);
    Person p2("bbb", 20);
    Person p3("ccc", 30);
    Person p4("ddd", 40);
    v.push_back(p1);
    v.push_back(p2);
    v.push_back(p3);
    v.push_back(p4);

    vector<Person>::iterator it = find_if(v.begin(), v.end(), Greater20());
    if(it == v.end())
    {
        cout << "未找到" << endl;
    }
    else
    {
        cout << "找到了：" << endl;
        cout << "name:" << it->name << " age:" << it->age << endl;
    }
}


int main()
{
    test522();
    test522_2();

    system("pause");
    return 0;
}