static

#define _CRT_SECURE_NO_WARNINGS
#include<iostream>
#include<cstring>
using namespace std;
class Date {
	private:
		int m_nYear, m_nMonth, m_nDay;
public:
	Date(int y, int m, int d);
	Date(Date &con_date);
};
Date::Date(int y, int m, int d)
{
	cout << "date constructor" << endl;
	m_nDay = d;
	m_nMonth = m;
	m_nYear = y;
}
Date::Date(Date &con_date)
{
	m_nYear = con_date.m_nYear;
	m_nDay = con_date.m_nDay;
	m_nYear = con_date.m_nYear;
}
class Student {
public:
	static int s_nTotalNum;
	Student(char *con_name, int con_id, Date &con_birthday);
	~Student();
private:
	char m_gName[20];
	int m_nID;
	Date m_iBirthday;
};
int Student::s_nTotalNum = 0;
Student::Student(char *con_name, int con_id, Date &con_birthday):m_iBirthday(con_birthday)
{
	int namelen = strlen(con_name) + 1;
	strcpy(m_gName, con_name);
	m_nID = con_id;
	s_nTotalNum++;
}
Student::~Student()
{
	s_nTotalNum--;
	cout << "destructor,totalnum= " << s_nTotalNum << endl;
	if (s_nTotalNum == 0)
		system("pause");
}
int main()
{
	Date tombirthday(1998, 5, 20);
	Student std_tom("Tom", 1, tombirthday);
	cout << "tom,the totalnum=" << std_tom.s_nTotalNum << endl;
	Date paulbirthady(1998, 4, 12);
	Student std_paul("Paul",2,tombirthday);
	cout << "paul,the totalnum" << std_paul.s_nTotalNum << endl;
	return 0;
}

#define _CRT_SECURE_NO_WARNINGS
#include<iostream>
#include<string>
using namespace std;
class Student {
public:
	Student(string con_name, int con_id);
	~Student();
	string get_stdname();
	static int get_totalnum();
	static int get_totalnum(Student&stdref);
private:
	static int s_ntotalnum;
	string m_strName;
	int m_nId;
};
int Student::s_ntotalnum = 0;
Student::Student(string con_name, int con_id) :m_strName(con_name)
{
	s_ntotalnum++;
	m_nId = con_id;
}
Student::~Student()
{
	s_ntotalnum--;
	cout << "destructor,totalnum= " << s_ntotalnum << endl;
	if (s_ntotalnum == 0)
		system("pause");
}
string Student::get_stdname()
{
	return m_strName;
}
int Student::get_totalnum()
{
	return s_ntotalnum;
}
int Student::get_totalnum(Student &stdref)
{
	cout << stdref.m_strName << "entered" << endl;
	return s_ntotalnum;
}
int main()
{
	cout << Student::get_totalnum()<< endl;
	Student std("Tom", 20);
	cout << std.get_stdname() << ' ' << std.get_totalnum(std) << endl;
	return 0;
}