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Problem with exception/writing violation

ADHDguitar (4)
Hello, I am currently taking an introductory C++ course in college and am working on the final project but have run into an error.

I am using Windows 7 64-bit and am compiling in VS 2010.

The error occurs in CentOS using Emacs as well. (Which is what I will be graded in.)

It is a Rock, Paper Scissors game where the user can play a game against a second player or the computer. Each game is comprised of 3 rounds. The error occurs when a player wins a match for a second time. It does not occur when the computer wins more than once.

I receive the following error message.

Unhandled exception at 0x58bacac8 (msvcr100d.dll) in project2.exe: 0xC0000005: Access violation writing location 0xcccccccc.



The debug screen shows the error happening in this section.
mov [edi+ecx*4-4],eax ;U - put dword into destination



Now, I am a beginner, so I haven't the faintest idea what that means.


Here is the code in which the error is happening. 

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case 2://Play 1-Player Game
			{
			//Highscore profile
			HighScore NewScore;

			//Start Game
			cout << endl
				<< "Game Start!"
				<< endl;

			//Scores
			PlayerScores Game = {0,0};

			

			for(int i = 0; i<3; i++)//Drive game
			{
				gameChoice p1Choice;
				gameChoice p2Choice;
				cout << "Round " << i+1 << endl
					<< endl;

				//Player Choice
				p1Choice=getChoice();

				//Computer Choice
				p2Choice=cpuChoice();

				gameChoice Rock=ROCK;

				//Calculate winner
				CalculateScores(p1Choice, Rock, Game);

				//Display choices
				cout << "You chose " << itemName[p1Choice]
					<< endl << "Your opponent chose " << itemName[p2Choice]
					<< endl;

				if(i!=2)
					cout << "Current score: "
						<< endl << name << ": " << Game.p1Score
						<< endl << "Opponent: " << Game.p2Score
						<< endl << endl;
			}

			//Display result message
			if(Game.p1Score>Game.p2Score)
			{
				cout << "You are the winner!";
				activeScores.p1Score++;
			}

			else if(Game.p1Score==Game.p2Score)
				cout << "It's a tie!";

			else
				cout << "You lost!";

			cout << endl << endl;


			//Display final score
			cout << "Final Score: "
						<< endl << name << ": " << Game.p1Score
						<< endl << "Opponent: " << Game.p2Score
						<< endl << endl;

			//Create Highscore entry
			NewScore.name=name;
			NewScore.score=activeScores.p1Score;

			//Update
			UpdateScores(currentScores,NewScore,3);

			cout << "Press ENTER to continue...";
			cin.ignore(80,'\n');
			cin.get(); //Wait for user to press Enter key to move on
			cin.ignore(80,'\n');
			cout << endl << endl << endl;
			
			//end game
			break;
			}



This is only the code for a single-player game, but the error occurs the same way in the multi-player game, therefore the error should be equally noticeable in this section.


Here are the function definitions. 

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/*
int random(int max)
Calculates a random number from 1 to max

Parameters:
	max, value parameter for highest possible value

Return Type: int for random number from 1 to max
*/

int random(int max)
{
	int r;

	//Feed random number generator 
	srand(time(NULL));
	//generate number from 1 to max
	r = rand() % max + 1;
	cout << r;
	return r;
}


/*
void CalculateScores(gameChoice p1Choice, gameChoice p2Choice,
					 PlayerScores& scores)
Determines winner based on choice of weapon

Parameters:
	p1Choice: Value Parameter for player 1 choice
	p2Choice: Value Parameter for player 2 choice
	scores: Reference Parameter for where score is updated

Return type: void
*/
void CalculateScores(gameChoice p1Choice, gameChoice p2Choice,
					 PlayerScores& scores)
{
	//Table of outcomes
	PlayerScores pscores[3][3]=
	{
		{//P1 picks Rock
			{0,0},{0,1},{1,0}
		},
		{//P1 picks Paper
			{1,0},{0,0},{0,1}
		},
		{//P1 picks Scissors
			{0,1},{1,0},{0,0}
		},
							};

	//find the winner
	scores.p1Score += pscores[p1Choice][p2Choice].p1Score;
	scores.p2Score += pscores[p1Choice][p2Choice].p2Score;
}

/*
void UpdateScores(HighScore Old[], HighScore New, int size)
Insert current score into Highscores if high enough.

Parameters:
	Old: Old Highscores read from text file
	New: New Highscores to compare to old
	size: Number of Highscore entries

Return Type: void
*/
void UpdateScores(HighScore Old[], HighScore New, int size)
{
	//Check scores
	for(int i = 0; i<size; i++)
	{
		if(New.score>Old[i].score)
		{
			for(int ii=size; ii>i; i++)
			{
				Old[ii].score=Old[ii-1].score;
				Old[ii].name=Old[ii-1].name;
			}
			Old[i].score=New.score;
			i=size;
		}
	}

}

/*
ofstream GetHighscores(HighScore Score[], int size)
Read Highscores from file, if file does not exist, create it. 
Return file for later output

Parameters: 
	Score: array of scores to store new scores
	Size: size of array

Return Type: void
*/

void GetHighscores(HighScore Score[], int size)
{
	ofstream outFile;
	ifstream inFile;
	//Read the file
	inFile.open("highscore.txt");

	//Check if file doesn't exist
	if(!inFile)
	{
		inFile.close();
		//Create file
		outFile.open("highscore.txt");
		outFile << "Bob" << endl;
		outFile << 3;
		outFile << "Joe" << endl;
		outFile << 2;
		outFile << "Smith" << endl;
		outFile << 1;
		outFile.close();
		inFile.open("highscore.txt");
	}
	//read contents of file
	for (int i=0;i<size;i++){
		getline(inFile, Score[i].name);

		inFile >> Score[i].score;
	}
	
	//Close infile and open outfile
	inFile.close();
}

/*
gameChoice getChoice()
Prompts user for selection.

Parameters:
	None

Return Type: gameChoice enum type for Players choice
*/
gameChoice getChoice()
{
	gameChoice pChoice;
	int gameMenu=-4;

	//Menu
	while(gameMenu>3 || gameMenu<1)//Prompt user for input
	{
		cout << "1. Rock"
			<< endl << "2. Paper"
			<< endl << "3. Scissors"
			<< endl; //Display menu

		cout << "Enter your choice: ";
		cin >> gameMenu;//User input

		if(gameMenu>3 || gameMenu<1)
		cout << "Error: Invalid input."
			<< endl;
	}

	cout << endl;


	//Set player selection
	if(gameMenu==1)
		pChoice=ROCK;
	if(gameMenu==2)
		pChoice=PAPER;
	if(gameMenu==3)
			pChoice=SCISSORS;

	return pChoice;
}


/*
gameChoice cpuChoice()
Gets cpu selection.

Parameters:
	None.

Return Type: gameChoice enum type
*/

gameChoice cpuChoice()
{
	gameChoice pChoice;
	int gameMenu;

	gameMenu=random(3);

	if(gameMenu==1)
		pChoice=ROCK;
	if(gameMenu==2)
		pChoice=PAPER;
	if(gameMenu==3)
		pChoice=SCISSORS;

	return pChoice;

}




And here is the header and struct/enum definitions. 

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enum gameChoice{ROCK,PAPER,SCISSORS}; //game choices

struct PlayerScores{
	int p1Score;
	int p2Score;
};

struct HighScore{ //Single score in highscores
	string name;
	int score;
};

gameChoice getChoice(); //Gets user choice

gameChoice cpuChoice(); //gets cpu choice




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int main()
{
	//Constants
	const string itemName[3] = {"Rock","Paper","Scissors"};

	//Variables
	int menu;
	string name;

	//Scores
	HighScore currentScores[3];
	PlayerScores activeScores={0,0};
	
	//Txt File
	ofstream outFile;
	GetHighscores(currentScores, 3);

	cout << "Welcome to Rock, Paper, Scissors." << endl;

	//Get name
	cout << "Enter your name: ";
	getline(cin,name);

.......


Sorry for the length. I tried to leave out anything unnecessary.

It would be great if I can get some kind of idea of how to fix this. Thank you in advance.
Last edited on
helios (17574)
I can't tell where the bug is from the code you've posted, but it's pretty clear that you're trying to dereference an uninitialized pointer somewhere.
That's as best as I can narrow it down from the information you've provided.
ADHDguitar (4)
Thank you for the reply. I didn't actually use * to declare any pointers anywhere, so would it be correct to say that it is probably stemming from a reference parameter somewhere?
Last edited on
helios (17574)
Yes. References often get compiled into equivalent pointer-based code.
ADHDguitar (4)
The error does not occur if the line


activeScores.p1Score++;


is removed.


Does that open any more possibilities?
helios (17574)
Check how it's being initialized.
ADHDguitar (4)
I found the problem. The function UpdateScores compared that value to the current highscore spot, and if it was higher, it entered a for loop to replace the current highscore(s) with the new one.


The error was in the for loop which only happened if that value was incremented.

I made two mistakes. The first was getting the number of elements in an array mixed up with the indices, forgetting to ad a "-1" to the index of one.

The second was putting "++" where "--" should have gone in one of the for loops.


That was a lot of headache for a small problem, but that's programming for you.


Thanks for all the help.
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