C++primer 7.3.4節練習

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練習7.32

標頭檔

 1 #pragma once 2 #include <vector> 3  4  5 class Screen { 6     friend class Window_mgr; 7     typedef std::string::size_type pos; 8 public: 9     //建構函式10     Screen() = default;11     Screen(pos h, pos w) : height(h), width(w), contents(h * w, ‘ ‘) {};12     Screen(pos h, pos w, char c) : height(h), width(w), contents(h * w, c) {};13     Screen(std::string &s);14     //成員函數15     Screen &move(pos r, pos c);16     Screen &set(pos r, pos c, char ch);17     char getChar(pos x, pos y) const;18     char getChar()const {19         return contents[(x_axis - 1)*y_axis + x_axis];20     }21     Screen &display(std::ostream &os)22     {23         os << contents;24         return *this;25     }26 27 28 private:29     std::string contents;30     pos height = 0;31     pos width = 0;32     pos x_axis = 0;33     pos y_axis = 0;34     //void do_display(std::ostream &os) const { os << contents; }35 };36 37 class Window_mgr {38 public:39     void clear(int i);40 private:41     std::vector<Screen> screens{ Screen(3,4,‘#‘) };42 };

 

源檔案

 1 #include <iostream> 2 #include <string> 3 #include "screen.h" 4  5 using namespace std; 6  7 int main() 8 { 9     Screen myScreen(5, 5, ‘X‘);10     myScreen.move(4, 0).set(3, 4, ‘#‘).display(cout);11     cout << "\n";12     myScreen.display(cout);13     cout << "\n";14     Window_mgr w1;15     w1.clear(0);16     system("pause");17     return 0;18 }19 20 Screen::Screen(string &s)21 {22     (*this).contents = s;23 }24 25 inline Screen &Screen::move(pos r, pos c)26 {27     x_axis = r;28     y_axis = c;29     return *this;30     // TODO: 在此處插入 return 語句31 }32 33 inline Screen &Screen::set(pos r, pos c, char ch)34 {35     contents[(r - 1) * c + r] = ch;36     return *this;37     // TODO: 在此處插入 return 語句38 }39 40 inline  char Screen::getChar(pos x, pos y) const41 {42     return contents[(x_axis - 1) * y_axis + x_axis];43     // TODO: 在此處插入 return 語句44 }45 46 void Window_mgr::clear(int i)47 {48     Screen &s = screens[i];49     s.contents = string(s.height * s.width, ‘ ‘);50 }

其實這裡是有問題的，問題在於如果使用window_mgr類的成員函數作為Screen類的友元，在定義順序完全正確的情況下，由於在window_mgr內需要使用到Screen類型，但是此時並沒有對Screen類進行聲明定義，所以會發生錯誤，以當前的知識儲備還不能解決之一問題，需要更多的學習

C++primer 7.3.4節練習