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Polymorphism/inheritance

Explodey (36)
I made this game that's supposed to help guitarists learn all the chord and scale forms, and I've been trying to make the more advanced levels of my game more challenging. I decided that I needed two of the member functions in my struct to function differently when the user gets past level 4, and it occurred to me that this is a perfect opportunity to try out polymorphism. I'm still pretty new to C++, and I learned about polymorphism a few months ago, but I couldn't think of a use for it until now.

I have a struct called Scaleform and I'm trying to create a derived class called AdvScaleForm that's the same except that the member functions RootWack and ShowRootCand are different. So I followed the example in my C++ book: I made those two functions virtual, and I made new versions of the functions and put them into struct AdvScaleForm:public ScaleForm. And I changed my class object to a pointer. But I got this compile error: "no matching function for call to 'AdvScaleForm::AdvScaleForm(int&, int&, int&)'" for this line:
pSf.push_back(new AdvScaleForm(pos, form, mode));

It seems like it's not finding the class constructor, but I don't know why because I thought the constructor was automatically inherited. Here's a truncated version of my structs and main(). I'm assuming the problem is in the AdvScaleForm part, which is shown in its entirety. Thanks for your help.

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struct ScaleForm
{
	short int m_Fingering[5][3];
	short int m_Length[5];
	short int m_UsrFingering[5][3];
	short int m_UsrLength[5];
	short int m_RootCand[5][5];
	short int m_Form, m_Span, m_Position, m_RootNum, m_Mode, m_CandSt, m_CandFr, m_LastCand1, m_LastCand2, m_Goal, m_WhackCurrent, m_Correct;
	int m_WhackGuess;
	unsigned long int m_Goodtime;
	bool m_Wack, m_First;
	
	ScaleForm(short int, short int, short int);
	void ShowAnswer();
	void ShowUsr(bool);
	bool HearAnswer();
	bool HearUsr();
	void ShowString(short int str, short int fing[][3]);
	short int HearString(short int str, short int fing[][3]);
	void ShowGhost(short int, short int);
	void ShowMarkers();
	bool UpdateUsr(short int, short int);
	short int GetUsrLength(short int);
	bool IsCorrect();
	bool IsStringFull(short int);
	bool IsSpanFull(short int);
	bool AreAllFull();
	short int GetNext(short int);
	short int GetRndNext();
	void ShowNext(short int, short int);
	bool virtual RootWack(bool);
	short int virtual ShowRootCand();
	void ShowRootStar();
	void ShowGood();
	void WackInfo();
};

ScaleForm::ScaleForm(short int posit, short int frm, short int mode)
{
	m_Form = frm;
	m_Span = ALL_SPANS[frm];
	m_Position = posit;
	m_Mode = mode;
	m_RootNum = ROOT_NUMBERS[frm] + posit;
	m_Goal = WHACK_GOALS[level];
	m_WhackCurrent = WHACK_START_LEVELS[level];
	m_WhackGuess = -1;
	m_Correct = 1;
	m_First = false;
	
	// etc, etc...
}

// a bunch of member functions removed...

bool ScaleForm::RootWack(bool goodness)
{
	// the original version of my virtual member function goes here.
}

short int ScaleForm::ShowRootCand()
{	
	// the original version of my other virtual member function goes here.
}

// more member functions removed...

/*
* below is the complete text of my derived class. nothing was removed.
* but you probably won't need to look at all the member function code,
* as I've already verified that the functions themselves work fine
* if I put them into the parent class (with the "ScaleForm::" prefix
* removed from all the member function calls).
*/

struct AdvScaleForm:public ScaleForm
{
	bool virtual RootWack(bool);
	short int virtual ShowRootCand();
};

bool AdvScaleForm::RootWack(bool goodness)
{
	short int z = -1;
	unsigned long int time_initial;
	m_Wack = false;
	m_Goodtime = 0;
	m_WhackGuess = -1;
	m_First = true;
	
	while ((!m_Wack) && (z != 1) && (z != 3) && (z != 5))
	{
		if (goodness)
		{
			goodness = false;
			m_Goodtime = SDL_GetTicks();
			apply_surface( 0, 0, background, screen );
			apply_surface(-20, 150, neck, screen);
			ScaleForm::ShowAnswer();
			ScaleForm::ShowMarkers();
			ScaleForm::ShowGood();
			ScaleForm::ShowRootStar();
			ScaleForm::WackInfo();
			SDL_Flip(screen);
			SDL_Delay(500);
		}
		
		apply_surface(0, 0, background, screen);
		apply_surface(-20, 150, neck, screen);
		ScaleForm::ShowAnswer();
		ScaleForm::ShowMarkers();
		ScaleForm::ShowGood();
		ScaleForm::WackInfo();
		SDL_Flip(screen);
		SDL_Delay(100);
		
		if (m_First)
		{
			Mix_PlayMusic(rootWhackMusic[m_WhackCurrent], -1);
		}
		
		apply_surface( 0, 0, background, screen );
		apply_surface(-20, 150, neck, screen);
		ScaleForm::ShowAnswer();
		ScaleForm::ShowMarkers();
		ScaleForm::ShowGood();
		ScaleForm::WackInfo();
		
		do 
		{
			m_CandSt = rand() % 5;
			m_CandFr = rand() % 5;
			z = ShowRootCand();
		} while (z == -1);
		
		SDL_Flip(screen);
		
		time_initial = SDL_GetTicks();
		m_Wack = false;
		
		while ((SDL_GetTicks() - time_initial) < WACK_RATES[m_WhackCurrent])
		{
			if ((SDL_PollEvent(&event)) && (event.type == SDL_KEYDOWN))
			{
				m_WhackGuess = event.key.keysym.sym;
				
				if ((m_WhackGuess == 49) || (m_WhackGuess == 51) || (m_WhackGuess == 53) || (m_WhackGuess == 257) || (m_WhackGuess == 259) || (m_WhackGuess == 261))
				{
					m_Wack = true;
					if (m_WhackGuess < 54)
					{
						m_WhackGuess -= 48;
					}
					else 
					{
						m_WhackGuess -= 256;
					}
					break;
				}
				else 
				{
					m_WhackGuess = -1;
				}
			}
		}
	}
		
	if (m_WhackGuess == z)
	{
		whackNum++;
		m_WhackCurrent++;
		m_Correct = m_WhackGuess;
		Mix_HaltMusic();
		if (whackNum < m_Goal)
		{
			Mix_PlayChannel(-1, winNote[NOTE_MAP[m_CandSt][m_CandFr + m_Position]], 0);
		}
		else 
		{
			Mix_PlayChannel(-1, noteSnd[NOTE_MAP[m_CandSt][m_CandFr + m_Position]], 0);
		}
	}
	
	return (m_WhackGuess == z);
}

short int AdvScaleForm::ShowRootCand()
{
	if ((m_CandSt == m_LastCand1) && (m_CandFr == m_LastCand2))
	{
		return -1;
	}
	
	if (m_RootCand[m_CandSt][m_CandFr] != -1)
	{
		if ((m_First) && (m_RootCand[m_CandSt][m_CandFr] == 1))
		{
			return -1;
		}
		
		m_First = false;
		
		m_LastCand1 = m_CandSt;
		m_LastCand2 = m_CandFr;
		
		if ((m_CandFr == 1) || (m_CandFr == 3))
		{
			apply_surface(FRETS[m_CandFr + m_Position - 1], STRINGS[m_CandSt][m_CandFr + m_Position - 1] - 20, rightRootStar[0][DOT_WIDTH[m_CandFr + m_Position - 1]], screen);
			if (m_CandSt == 0)
			{
				apply_surface(FRETS[m_CandFr + m_Position - 1], STRINGS[5][m_CandFr + m_Position - 1] - 20, rightRootStar[0][DOT_WIDTH[m_CandFr + m_Position - 1]], screen);
			}
		}
		else 
		{
			apply_surface(FRETS[m_CandFr + m_Position] - 20, STRINGS[m_CandSt][m_CandFr + m_Position] - 20, rootStar[0], screen);
			if (m_CandSt == 0)
			{
				apply_surface(FRETS[m_CandFr + m_Position] - 20, STRINGS[5][m_CandFr + m_Position] - 20, rootStar[0], screen);
			}
		}
		
		if ((m_RootCand[m_CandSt][m_CandFr] != 1) && (m_RootCand[m_CandSt][m_CandFr] != 3) && (m_RootCand[m_CandSt][m_CandFr] != 5))
		{
			return 0;
		}
	}
	
	return m_RootCand[m_CandSt][m_CandFr];
}

vector<ScaleForm*> pSf;
int level;

int main(int argc, char* args[])
{
	int form, lastForm, pos, mode;
	
	srand(static_cast<unsigned int> (time(0)));
	
	for (level = 0; level < 9; level++)
	{
		while (lastForm == form)
		{
			form = (rand() % FORM_LEVELS[0][level]) + FORM_LEVELS[1][level];
			pos = rand() % 7;
			mode = rand() % 2;
		}
		
		pSf.clear();
		if (level < 4)
		{
			pSf.push_back(new ScaleForm(pos, form, mode));
		}
		else 
		{
			pSf.push_back(new AdvScaleForm(pos, form, mode));
		}
		
	// stuff taken out....
	}
}
Last edited on
LB (13399)
Constructors in C++ are not inherited. In C++11 you can explicitly inherit constructors.
Last edited on
Explodey (36)
Okay, I just tried copying the constructor from ScaleFrom and pasting it into AdvScaleForm but now I'm getting this error, "no matching function for call to 'ScaleForm::ScaleForm()'" for this line (which is the constructor definition in my derived class):

AdvScaleForm::AdvScaleForm(short int posit, short int frm, short int mode)

Here's the full code for my derived class now:

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struct AdvScaleForm:public ScaleForm
{
	AdvScaleForm(short int, short int, short int);
	bool virtual RootWack(bool);
	short int virtual ShowRootCand();
};

AdvScaleForm::AdvScaleForm(short int posit, short int frm, short int mode)
{
	m_Form = frm;
	m_Span = ALL_SPANS[frm];
	m_Position = posit;
	m_Mode = mode;
	m_RootNum = ROOT_NUMBERS[frm] + posit;
	m_Goal = WHACK_GOALS[level];
	m_WhackCurrent = WHACK_START_LEVELS[level];
	m_WhackGuess = -1;
	m_Correct = 1;
	m_First = false;
	
	if (mode == 1)
	{
		m_RootNum -= 3;
	}
	
	m_LastCand1 = -1;
	m_LastCand2 = -1;
	
	short int x = 0;
	short int it, it2;
	
	for (it = 0; it < 5; it++)
	{
		for (it2 = 0; it2 < 3; it2++)
		{
			m_Fingering[it][it2] = SYMBOLS[frm][x];
			m_UsrFingering[it][it2] = -1;
			x++;
		}
	}
	
	x = 0;
	for (it = 0; it < 5; it++)
	{
		for (it2 = 0; it2 < 5; it2++)
		{
			m_RootCand[it][it2] = ROOT_FINDER[mode][frm][x];
			x++;
		}
	}
	
	for (it = 0; it < 5; it++)
	{
		m_Length[it] = ALL_LENGTHS[frm][it];
		m_UsrLength[it] = 0;
	}
}

bool AdvScaleForm::RootWack(bool goodness)
{
	short int z = -1;
	unsigned long int time_initial;
	m_Wack = false;
	m_Goodtime = 0;
	m_WhackGuess = -1;
	m_First = true;
	
	while ((!m_Wack) && (z != 1) && (z != 3) && (z != 5))
	{
		if (goodness)
		{
			goodness = false;
			m_Goodtime = SDL_GetTicks();
			apply_surface( 0, 0, background, screen );
			apply_surface(-20, 150, neck, screen);
			ScaleForm::ShowAnswer();
			ScaleForm::ShowMarkers();
			ScaleForm::ShowGood();
			ScaleForm::ShowRootStar();
			ScaleForm::WackInfo();
			SDL_Flip(screen);
			SDL_Delay(500);
		}
		
		apply_surface(0, 0, background, screen);
		apply_surface(-20, 150, neck, screen);
		ScaleForm::ShowAnswer();
		ScaleForm::ShowMarkers();
		ScaleForm::ShowGood();
		ScaleForm::WackInfo();
		SDL_Flip(screen);
		SDL_Delay(100);
		
		if (m_First)
		{
			Mix_PlayMusic(rootWhackMusic[m_WhackCurrent], -1);
		}
		
		apply_surface( 0, 0, background, screen );
		apply_surface(-20, 150, neck, screen);
		ScaleForm::ShowAnswer();
		ScaleForm::ShowMarkers();
		ScaleForm::ShowGood();
		ScaleForm::WackInfo();
		
		do 
		{
			m_CandSt = rand() % 5;
			m_CandFr = rand() % 5;
			z = ShowRootCand();
		} while (z == -1);
		
		SDL_Flip(screen);
		
		time_initial = SDL_GetTicks();
		m_Wack = false;
		
		while ((SDL_GetTicks() - time_initial) < WACK_RATES[m_WhackCurrent])
		{
			if ((SDL_PollEvent(&event)) && (event.type == SDL_KEYDOWN))
			{
				m_WhackGuess = event.key.keysym.sym;
				
				if ((m_WhackGuess == 49) || (m_WhackGuess == 51) || (m_WhackGuess == 53) || (m_WhackGuess == 257) || (m_WhackGuess == 259) || (m_WhackGuess == 261))
				{
					m_Wack = true;
					if (m_WhackGuess < 54)
					{
						m_WhackGuess -= 48;
					}
					else 
					{
						m_WhackGuess -= 256;
					}
					break;
				}
				else 
				{
					m_WhackGuess = -1;
				}
			}
		}
	}
		
	if (m_WhackGuess == z)
	{
		whackNum++;
		m_WhackCurrent++;
		m_Correct = m_WhackGuess;
		Mix_HaltMusic();
		if (whackNum < m_Goal)
		{
			Mix_PlayChannel(-1, winNote[NOTE_MAP[m_CandSt][m_CandFr + m_Position]], 0);
		}
		else 
		{
			Mix_PlayChannel(-1, noteSnd[NOTE_MAP[m_CandSt][m_CandFr + m_Position]], 0);
		}
	}
	
	return (m_WhackGuess == z);
}

short int AdvScaleForm::ShowRootCand()
{
	if ((m_CandSt == m_LastCand1) && (m_CandFr == m_LastCand2))
	{
		return -1;
	}
	
	if (m_RootCand[m_CandSt][m_CandFr] != -1)
	{
		if ((m_First) && (m_RootCand[m_CandSt][m_CandFr] == 1))
		{
			return -1;
		}
		
		m_First = false;
		
		m_LastCand1 = m_CandSt;
		m_LastCand2 = m_CandFr;
		
		if ((m_CandFr == 1) || (m_CandFr == 3))
		{
			apply_surface(FRETS[m_CandFr + m_Position - 1], STRINGS[m_CandSt][m_CandFr + m_Position - 1] - 20, rightRootStar[0][DOT_WIDTH[m_CandFr + m_Position - 1]], screen);
			if (m_CandSt == 0)
			{
				apply_surface(FRETS[m_CandFr + m_Position - 1], STRINGS[5][m_CandFr + m_Position - 1] - 20, rightRootStar[0][DOT_WIDTH[m_CandFr + m_Position - 1]], screen);
			}
		}
		else 
		{
			apply_surface(FRETS[m_CandFr + m_Position] - 20, STRINGS[m_CandSt][m_CandFr + m_Position] - 20, rootStar[0], screen);
			if (m_CandSt == 0)
			{
				apply_surface(FRETS[m_CandFr + m_Position] - 20, STRINGS[5][m_CandFr + m_Position] - 20, rootStar[0], screen);
			}
		}
		
		if ((m_RootCand[m_CandSt][m_CandFr] != 1) && (m_RootCand[m_CandSt][m_CandFr] != 3) && (m_RootCand[m_CandSt][m_CandFr] != 5))
		{
			return 0;
		}
	}
	
	return m_RootCand[m_CandSt][m_CandFr];
}
LB (13399)
When you provide your own constructor, the ones the compiler would have provided for you are not provided. Prior to C++11 you need to manually add your default constructor, but in C++11 and above you an explicitly ask the compiler to generate it for you.

You may want to reread the tutorial on this site as it covers the problems you're running into.
Last edited on
Explodey (36)
Woo hoo! I checked my book again and I managed to figure it out. I just needed to change my constructor to this:

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AdvScaleForm::AdvScaleForm(short int posit, short int frm, short int mode):
ScaleForm(posit, frm, mode)
{}


Thanks for your help.
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