CODEWITHSUNDEEP
c++c++11
lmarchesoti
lmarchesoti

Reputation: 16

c++ declaring class member outside class

I have these two examples from c++ primer, trying to declare a class member function outside the class definition. The first one gives me an error even when I remove the friendship and definition. The second one works fine. Any hints?

Error:

src/Screen.h:16:47: error: no ‘void Window_mgr::clear(Window_mgr::ScreenIndex)’ member function declared in class ‘Window_mgr’

Ex1:

#ifndef SCREEN_H
#define SCREEN_H
#include <string>
#include <vector>
class Screen;

class Window_mgr {

public:
    using ScreenIndex = std::vector<Screen>::size_type;
    Window_mgr();
private:
    std::vector<Screen> screens;
};

void Window_mgr::clear(Window_mgr::ScreenIndex);
class Screen {

    //friend void Window_mgr::clear(ScreenIndex);

public:
    using pos = std::string::size_type;
    Screen() = default;
    Screen(pos h, pos w): height(h), width(w), contents(h*w, ' ') { }
    Screen(pos h, pos w, char c): height(h), width(w), contents(h*w, c) { }
    char get() const { return contents[cursor]; }
    inline char get(pos, pos) const;
    Screen &move(pos, pos);
    Screen &set(char c) { contents[cursor] = c; return *this; }
    Screen &set(pos, pos, char);
    const Screen &display(std::ostream &os) const { do_display(os); return *this; }
    Screen &display(std::ostream &os) { do_display(os); return *this; }
    pos size() const;

private:
    const void do_display(std::ostream &os) const { os << contents; }
    pos cursor = 0;
    pos height = 0, width = 0;
    std::string contents;
};

inline
Window_mgr::Window_mgr(): screens{Screen(24, 80, ' ')} { }

char Screen::get(pos r, pos c) const
{ pos row = r * width; return contents[row + c]; }

inline Screen& Screen::move(pos r, pos c)
{ pos row = r * width; cursor = row + c; return *this; }

inline Screen& Screen::set(pos r, pos c, char ch)
{ pos row = r * width; contents[row + c] = ch; return *this; }

//inline void Window_mgr::clear(ScreenIndex i)
//{ Screen &s = screens[i]; s.contents = std::string(s.height * s.width, ' '); }

inline Screen::pos Screen::size() const
{ return height * width; }
#endif

Ex2:

#include <iostream>

int height;
class Screen {
public:
  typedef std::string::size_type pos;
  void set_height(pos);
  pos height = 0;
};
Screen::pos verify(Screen::pos);
//void Screen::set_height(pos var) { height = verify(var); }

//Screen::pos verify(Screen::pos a) { return a; }

int main(){

  return 0;
}

Upvotes: 0

Views: 8886

Answers (2)

Lightness Races in Orbit
Lightness Races in Orbit

Reputation: 385098

No hints available.

You simply cannot do that.

The class definition must be a full picture of the members contained within that class.

Upvotes: 0

Thinkeye
Thinkeye

Reputation: 928

You cannot declare member outside its class. You can define a member function outside of the class, if you have declared it inside. Second example simply defines a global function verify, which uses the public types from the class Screen, but itself is not a member of Screen.

Upvotes: 10

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