Bjarne Stroustrup PPP - 第9章鑽4 - cout枚舉錯誤

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我想解決Bjarne Stroustrups原理和實踐第2版的鑽4。出於某種原因，它不會讓我知道我之前初始化的月份和年份成員。我知道有使用枚舉的替代方法，但我想知道如何使用它。有人可以幫我嗎？乾杯Bjarne Stroustrup PPP - 第9章鑽4 - cout枚舉錯誤

// Philipp Siedler 
// Bjarne Stroustrup's PPP 
// Chapter 9 Drill 4 

#include "std_lib_facilities.h" 

class Year { 
    static const int min = 1800; 
    static const int max = 2200; 
private: 
    int y; 
public: 
    class Invalid {}; 
    Year(int x) : y{ x } { if (x < min || max <= x) throw Invalid{}; }; 
    int year() { return y; }; 
}; 

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

class Date { 
private: 
    Year y; 
    Month m; 
    int d; 
public: 
    Date(Year y, Month m, int d) : y(y), m(m), d(d) {}; 
    Year year() { return Year{ y }; }; 
    Month month() { return Month{ m }; }; 
    int day() { return d; }; 
    void add_day(int n); 
}; 

void Date::add_day(int n) { 
    d += n; 
} 

int main() 
try 
{ 
    Date today{ Year{ 1978 }, Month::jun, 25 }; 
    Date tomorrow = today; 

    tomorrow.add_day(1); 

    cout << "Year: " << today.year() << " Month: " << today.month() << " Day: " << today.day() << "\n"; 
    cout << "Year: " << tomorrow.year() << " Month: " << tomorrow.month() << " Day: " << tomorrow.day() << "\n"; 

    keep_window_open(); 
} 

catch (runtime_error e) { 
    cout << e.what() << '\n'; 
    keep_window_open(); 
} 
catch (...) { 
    cout << "Exiting" << '\n'; 
    keep_window_open(); 
}

來源

2017-05-28 Philipp Siedler

沒有'的std :: flush'ing？ – LogicStuff

我對編碼和C++很陌生，沒有談及std :: flush的話題。 –

@ Philipp Siedler您必須重載運算符<<以進行枚舉或更改函數month（），以便返回一個字符串與一個月份的名稱。 –

您好我只是理解了它自己，所以誰以往任何時候都需要使用相同的問題的幫助，這裏是一個潛在的解決方案和操作符重載的簡單的例子：

// Philipp Siedler 
// Bjarne Stroustrup's PPP 
// Chapter 9 Drill 4 

#include "std_lib_facilities.h" 

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

    Date(int y, Month m, int d); 
    void add_day(int n); 

    int year() const { return y; } 
    Month month() const { return m; } 
    int day() const { return d; } 

private: 
    int y; 
    Month m; 
    int d; 
}; 

Date::Date(int y0, Date::Month m0, int d0) { 
    d = d0; 
    m = m0; 
    y = y0; 
} 

void Date::add_day(int n) { 
    d += n; 
} 

static ostream & operator<< (ostream & os, const Date::Month & m) { 
    switch (m) { 
    case Date::jan: os << "January"; break; 
    case Date::feb: os << "February"; break; 
    case Date::mar: os << "March"; break; 
    case Date::apr: os << "April"; break; 
    case Date::may: os << "May"; break; 
    case Date::jun: os << "June"; break; 
    case Date::jul: os << "July"; break; 
    case Date::aug: os << "August"; break; 
    case Date::sep: os << "September"; break; 
    case Date::oct: os << "October"; break; 
    case Date::nov: os << "November"; break; 
    case Date::dec: os << "December"; break; 
    } 
    return os; 
} 

ostream & operator<< (ostream & os, const Date & dd) { 
    os << "Year: " << dd.year() << " Month: " << dd.month() << " Day: " << dd.day() << endl; 
    return os; 
} 

int main() 
try 
{ 
    Date today{ 1978, Date::jun, 25 }; 
    Date tomorrow = today; 
    tomorrow.add_day(1); 

    cout << today; 
    cout << tomorrow; 

    keep_window_open(); 
} 

catch (runtime_error e) { 
    cout << e.what() << '\n'; 
    keep_window_open(); 
} 
catch (...) { 
    cout << "Exiting" << '\n'; 
    keep_window_open(); 
}

來源

2017-05-29 15:45:41

Bjarne Stroustrup PPP - 第9章鑽4 - cout枚舉錯誤

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