f0904.cpp

it is a usefull thing

//=====================================
// f0904.cpp
// partial initialization of constructor
//=====================================
#include<iostream>
#include<iomanip>
using namespace std;
//-------------------------------------
class Date{
  int year, month, day;
  void init();
public:
  Date(const string& s);
  Date(int y=2000, int m=1, int d=1);
  bool isLeapYear()const;
  friend ostream& operator<<(ostream& o, const Date& d);
};//-----------------------------------
void Date::init(){
  if(year>5000 || year<1 || month<1 || month>12 || day<1 || day>31)
    exit(1);  // 停机
}//------------------------------------
Date::Date(const string& s){
  year = atoi(s.substr(0,4).c_str());
  month = atoi(s.substr(5,2).c_str());
  day = atoi(s.substr(8,2).c_str());
  init();
}//------------------------------------
Date::Date(int y, int m, int d){
  year=y, month=m, day=d;
  init();
}//------------------------------------
bool Date::isLeapYear()const{
  return (year % 4==0 && year % 100 )|| year % 400==0;
}//------------------------------------
ostream& operator<<(ostream& o, const Date& d){
  o<<setfill('0')<<setw(4)<<d.year<<'-'<<setw(2)<<d.month<<'-';
  return o<<setw(2)<<d.day<<'\n'<<setfill(' ');
}//------------------------------------
int main(){
  Date c("2005-12-28");
  Date d(2003,12,6);
  Date e(2002);
  Date f(2002,12);
  Date g;
  cout<<c<<d<<e<<f<<g;
}//====================================