ostream＆istream＆未正確定義

Question

編譯器給我以下錯誤消息：「未知類型名稱'ostream'和'未知類型名稱'istream' 還'使用未聲明的標識符'ios_base'。是否應該添加任何？。在頭文件頭的類型或將出現同樣的錯誤太多我不知道什麼是錯的，因爲我從字面上書中複製的代碼（本來） 這裏是我的代碼：

#include "chrono.h" 
//The definitions go into Chrono.cpp: 

// Chrono.cpp 

namespace Chrono { 

    // member function definitions: 

    Date::Date(int yy, Month mm, int dd) 
    :y{yy}, m{mm}, d{dd} 
    { 
     if (!is_date(yy,mm,dd)) throw Invalid{}; 
    } 

    const Date& default_date() 
    { 
     static Date dd {2001,Month::jan,1}; 
     return dd; 
    } 
    Date::Date() 
     :y{default_date().year()}, 
     m{default_date().month()}, 
     d{default_date().day()} 
    { 
    } 
    void Date:: add_day(int n) 
    { 
     //.. 
    } 
    void Date::add_month(int n){ 
     //.. 
    } 
    void Date::add_year(int n){ 
     if (m==feb && d==29 && !leapyear(y+n)) { // beware of leap years! 
      // makes sense for both positive and negative n (n==0 should be impossible here) 
      m = mar;  // use March 1 instead of February 29 
      d = 1; 
     } 
     y+=n; 
    } 
// helper functions 

    bool is_date(int y, Month m, int d) 
    { 
     // assume that y is valid 

     if (d<=0) return false;   // d must be positive 
     if (m<Month::jan || Month::dec<m) return false; 

     int days_in_month = 31;    // most months have 31 days 

     switch(m) { 
      case Month::feb: 
       days_in_month = (leapyear(y))?29:28; 
       break; 
      case Month::apr: case Month::jun: case Month::sep: case Month::nov: 
       days_in_month =30; 
       break; 
     } 
     if (days_in_month<d) return false; 

     return true; 
    } 

    bool leapyear(int y) 
    { 
     // see exercise 10 
    } 

    bool operator==(const Date& a, const Date& b) 
    { 
     return a.year()==b.year() 
     && a.month()==b.month() 
     && a.day()==b.day(); 
    } 


    bool operator!=(const Date& a, const Date& b) 
    { 
     return !(a==b); 
    } 

    ostream& operator<<(ostream& os, const Date& d) 
    { 
     return os << '(' << d.year() 
     << ',' << d.month() 
     << ',' << d.day()<<')'; 
    } 


    istream& operator>>(istream& is, Date& dd) 
    { 
     int y, m, d; 
     char ch1, ch2, ch3, ch4; 
     is >> ch1 >> y >> ch2 >> m >> ch3 >> d >> ch4; 
     if (!is) return is; 
     if (ch1!='(' || ch2!=',' || ch3!=',' || ch4!=')') { // oops: format error 
      is.clear(ios_base::failbit);     // set the fail bit 
      return is; 
     } 
     dd = Date(y,Month(m),d);  // update dd 
     return is; 
    } 

    enum class Day { 
     sunday,monday,tuesday,wednesday,thursday,friday,saturday 
    }; 

    Day day_of_week(const Date& d) 
    { 
     //.. 
    } 
    Date next_Sunday(const Date& d) 
    { 
     //.. 
    } 
    Date next_weekday(const Date& d) 
    { 
     //.. 
    } 

} 

這是頭文件

//chrono.h

namespace Chrono { 

    enum Month { 
     jan=1, feb, mar, apr, may, jun, jul, aug, sep, oct, nov, dec 
    }; 

    class Date { 
    public: 

     class Invalid { };     // to throw as exception 

     Date(int y, Month m, int d);  // check for valid date and initialize 
     Date();       // default constructor 
     // the default copy operations are fine 

     // non-modifying operations: 
     int day() const { return d; } 
     Month month() const { return m; } 
     int year() const { return y; } 

     // modifying operations: 
     void add_day(int n); 
     void add_month(int n); 
     void add_year(int n); 
    private: 
     int y; 
     Month m; 
     int d; 
    }; 

    bool is_date(int y, Month m, int d); // true for valid date 

    bool leapyear(int y);     // true if y is a leap year 

    bool operator==(const Date& a, const Date& b); 
    bool operator!=(const Date& a, const Date& b); 

    ostream& operator<<(ostream& os, const Date& d); 
    istream& operator>>(istream& is, Date& dd); 

    Date day_of_week(const Date& d);  // day of week of d 
    Date next_Sunday(const Date d);  // next Sunday after d 
    Date next_weekday(const date& d);  // next weekday after d 
}           

Answer 1

在你有一個頭加

#include <iosfwd> 

要轉發聲明輸入輸出流。並使用std::ostream和std::istream

在CPP - 你會用

#include <iostream> 

通過Barmar的建議。並且爲這個命名空間的成員指定命名空間std ::。