C++primer 7.3.4节练习
练习7.32
头文件
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 //构造函数 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 //成员函数 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 };
源文件
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: 在此处插入 return 语句 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: 在此处插入 return 语句 38 } 39 40 inline char Screen::getChar(pos x, pos y) const 41 { 42 return contents[(x_axis - 1) * y_axis + x_axis]; 43 // TODO: 在此处插入 return 语句 44 } 45 46 void Window_mgr::clear(int i) 47 { 48 Screen &s = screens[i]; 49 s.contents = string(s.height * s.width, ' '); 50 }
其实这里是有问题的，问题在于如果使用window_mgr类的成员函数作为Screen类的友元，在定义顺序完全正确的情况下，由于在window_mgr内需要使用到Screen类型，但是此时并没有对Screen类进行声明定义，所以会发生错误，以当前的知识储备还不能解决之一问题，需要更多的学习
