简单的程序诠释C++ STL算法系列之七:count_if
C++STL的非变易算法(Non-mutating algorithms)是一组不破坏操作数据的模板函数,用来对序列数据进行逐个处理、元素查找、子序列搜索、统计和匹配。
count_if算法是使用谓词判断pred统计迭代器区间[first , last) 上满足条件的元素个数n,按计数n是否引用返回,有如下两种函数原型:
函数原型:
template<class InputIterator, class Predicate>
typename iterator_traits<InputIterator>::difference_type count_if(
InputIterator _First,
InputIterator _Last,
Predicate _Pred
);
template<class InputIterator, class T> inline
size_t count(
InputIterator First,
InputIterator Last,
const T& Value
)
示例代码:
/*******************************************************************
* Copyright (C) Jerry Jiang
* File Name : count_if.cpp
* Author : Jerry Jiang
* Create Time : 2011-10-9 19:46:25
* Mail : jbiaojerry@gmail.com
* Blog : http://blog.csdn.net/jerryjbiao
* Description : 简单的程序诠释C++ STL算法系列之七
* 非变易算法: 条件统计容器元素个数count_if
******************************************************************/
#pragma warning(disable:4786)
#include <algorithm>
#include <map>
#include <iostream>
using namespace std;
//学生记录结构体
struct stuRecord{
struct stuInfo{
char* name;
int year;
char* addr;
};
int id; //学号
stuInfo m_stuInfo; //学生信息
stuRecord(int m_id, char* m_name, int m_year, char* m_addr)
{
id = m_id;
m_stuInfo.name = m_name;
m_stuInfo.year = m_year;
m_stuInfo.addr = m_addr;
}
};
typedef stuRecord::stuInfo stuRI;
bool setRange( pair<int, stuRI> s )
{
if (s.second.year > 20 && s.second.year < 30)
{
return true;
}
return false;
}
int main()
{
//学生数据
stuRecord stu1 = stuRecord(1, "张三", 21, "北京");
stuRecord stu2 = stuRecord(2, "李四", 29, "上海");
stuRecord stu3 = stuRecord(3, "王五", 12, "深圳");
stuRecord stu4 = stuRecord(4, "赵六", 25, "长沙");
stuRecord stu5 = stuRecord(5, "孙七", 30, "广东");
//插入学生记录
map<int, stuRI> m;
m.insert(make_pair(stu1.id, stu1.m_stuInfo));
m.insert(make_pair(stu2.id, stu2.m_stuInfo));
m.insert(make_pair(stu3.id, stu3.m_stuInfo));
m.insert(make_pair(stu4.id, stu4.m_stuInfo));
m.insert(make_pair(stu5.id, stu5.m_stuInfo));
//条件统计
int num = count_if(m.begin(), m.end(), setRange);
cout << "学生中年龄介于20至30之间的学生人数为:"
<< num << endl;
return 0;
} 摘自:Jerry.Jiang的程序人生
补充:软件开发 , C++ ,