C++ Primer 练习7.32（C++ Primer读书笔记）

第七章类

练习7.32 定义你自己的Screen和Window_mgr，其中clear是Window_mgr的成员，是Screen的友元。

由于Window_mgr中含有Screen对象，所以在Window_mgr之前要声明Screen。

因为clear中调用Screen成员，所以Screen要在clear定义之前定义。

因为Screen类中要声明友元函数clear，而clear是Window_mgr的成员函数，所以在Screen之前要定义Window_mgr。

好乱啊啊啊啊

代码：

#include <iostream>
#include <string>
#include <vector>
 
class Screen;
 
class Window_mgr {
public:
    using ScreenIndex = std::vector<Screen>::size_type;
    void clear(ScreenIndex);
private:
    std::vector<Screen> screens;//{Screen(24, 80, ' ')};
};
 
class Screen {
public:
    typedef std::string::size_type pos;
    Screen() = default;
    Screen(int ht, int wd) : height(ht), width(wd), contents(ht * wd, ' ') {}
    Screen(pos ht, pos wd, char c) : height(ht), width(wd), contents(ht * wd, c) {}
    char get() const    // 读取光标处的字符
    {
        return contents[cursor];
    }
    inline char get(pos ht, pos wd) const;
    Screen &move(pos r, pos c);
    void some_number() const;
    Screen &set(char);
    Screen &set(pos, pos, char);
    Screen &display(std::ostream &os)
    {
        do_display(os);
        return *this;
    }
    const Screen &display(std::ostream &os) const
    {
        do_display(os);
        return *this;
    }
    //friend class Window_mgr;
    friend void Window_mgr::clear(ScreenIndex);
private:
    pos cursor = 0;
    pos height = 0, width = 0;
    mutable size_t access_ctr;
    std::string contents;
    void do_display(std::ostream &os) const
    {
        os << contents;
    }
};
 
inline Screen &Screen::move(pos r, pos c)
{
    pos row = r * width;
    cursor = row + c;
    return *this;
}
 
char Screen::get(pos r, pos c) const
{
    pos row = r * width;
    return contents[row + c];
}
 
void Screen::some_number() const
{
    ++access_ctr;
}
 
inline Screen &Screen::set(char c)
{
    contents[cursor] = c;
    return *this;
}
 
inline Screen& Screen::set(pos r, pos col, char ch)
{
    contents[r * width + col] = ch;
    return *this;
}
 
void Window_mgr::clear(ScreenIndex i)
{
    Screen &s = screens[i];
    s.contents = std::string(s.height * s.width, ' ');
}
 
int main()
{
    Screen myscreen(5, 5, 'X');
    myscreen.move(4, 0).set('#').display(std::cout);
    std::cout << '\n';
    myscreen.display(std::cout);
    return 0;
}