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;
}
对于这一句
std::vector<Screen> screens{Screen(24, 80, ' ')};
暂时只能改成
std::vector<Screen> screens;
因为第一个需要调用构造函数，那样的话。。。Screen就要定义在Window_mgr前面。。。。我要疯了。。。。