C++Primer第五版 7.3.4节练习

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/*
*练习7.32
*2015/7/13
*问题描述：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。
*说明：仅说明写的程序用 ,写得不好
*作者：Nick Feng
*邮箱：nickgreen23@163.com
*
*/
#include <iostream>
#include <string>
#include <vector>
using namespace std;
class Window_mgr{
public:
void clear();
};
void Window_mgr::clear(){
cout << "clearing..." << endl;
}
class Screen{
public:
friend class Window_mgr;
friend void Window_mgr::clear();
};
int main()
{
Window_mgr a;
a.clear();
return 0;
}

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/*
*练习7.32
*2015/7/14
*问题描述：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。
*功能：做了点改进，便于理解。
*作者：Nick Feng
*邮箱：nickgreen23@163.com
*
*/
#include <iostream> 
#include <string>
#include <vector> 
using namespace std;
class Screen{
public:
typedef std::string::size_type pos;
Screen() = default;
Screen(pos ht, pos wd, char c) : height(ht), width(wd), contents(ht * wd, c){}
char get() const { return contents[cursor]; }
inline char get(pos ht, pos wd) const;
Screen &move(pos r, pos c);
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;
}
//extern void Window_mgr::clear(ScreenIndex);

//friend void Window_mgr::clear(ScreenIndex);
//friend void Window_mgr::clear(ScreenIndex);
//extern class Window_mgr;
friend class Window_mgr;
//extern void Window_mgr::clear(ScreenIndex);
private:
pos cursor = 0;
pos height = 0, width = 0;
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];
}
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;
}
//typedef std::vector<Screen>::size_type ScreenIndex;
class Window_mgr {
public:
typedef std::vector<Screen>::size_type ScreenIndex;
void clear(ScreenIndex);
void clear();
private:
std::vector<Screen> screens{Screen(24, 80,' ')};
};
void Window_mgr::clear(ScreenIndex i)
{
Screen &s = screens[i];
s.contents = string(s.height * s.width, ' ');
}
void Window_mgr::clear()
{
cout << "Nothing" << endl;
}
int main()
{
Screen test(5,5,'x');
test.display(cout);
Window_mgr a;
a.clear(0);
cout << endl;
return 0;
}