Segmentation Fault (Core dumped)

[bwilfong3]

I am going nuts finding out where the memory allocation error is here.
This program reads checkerboard data from a file into a 2d array, then uses recursion to count the number of white tiles in each area. (It also displays the board data).

#include <iostream>
#include <fstream>

using namespace std;

void readArray(int, int, char[][8]);
void displayContents(char[][8]);
int  countTiles(int, int, int, int, char[][8], bool[][8]);


int main()
{
   const int MAX_WIDTH = 8,
	     MAX_HEIGHT  = 8;

   int  tileCount[8][8] = {0};
   char boardContents[8][8] = {0};
   bool checkTiles[8][8] = {false};

   readArray(MAX_WIDTH, MAX_HEIGHT, boardContents);
   displayContents(boardContents);

   

   for (int i = 0; i < MAX_HEIGHT; i++)
   {
      for (int j = 0; j < MAX_WIDTH; j++)
      {
         tileCount[i][j] = countTiles(MAX_WIDTH, MAX_HEIGHT, i, 
                                     j, boardContents, checkTiles);
         checkTiles[i][j] = true;  //this line ensures the tile has been checked
      }
   }

}

// The following readArray() function will
// accept the height and width parameters
// of the board, along with the 2d array
// to contain the contents of the board.
// the required file is opened and read
// into the array.

void readArray(int HEIGHT, int WIDTH, char boardContents[8][8])
{
                        
   ifstream boardData;
   boardData.open("board.txt");

   if (!boardData)
      cout << "File open failure." << endl;

   for (int i = 0; i < WIDTH; i++)
      for (int j = 0; j < HEIGHT; j++)
         boardData >> boardContents[i][j];

   boardData.close();

}//end readArray()

//This function simply accepts the 2D array
//as an argument and displays the elements.

void displayContents(char boardContents[8][8])
{
   for (int i = 0; i < 8; i++)
   {
      for(int j = 0; j < 8; j++)
         cout << boardContents[i][j];

      cout << endl;
   }
}//end displayContents()

int countTiles(int WIDTH, int HEIGHT, int i, int j,
               char boardContents[8][8], bool checkTiles[8][8])
{
   bool outOfBounds = false;

   if (i < 0 || j < 0 || i >= 8 || j >= 8)
      outOfBounds = true;

   if (outOfBounds == true)
         return 0;

   else if (boardContents[i][j] == 'b' ||
            checkTiles[i][j]    == true)
         return 0;

   else
      return countTiles(WIDTH, HEIGHT, i + 1, j, boardContents, checkTiles)
           + countTiles(WIDTH, HEIGHT, i - 1, j, boardContents, checkTiles)
           + countTiles(WIDTH, HEIGHT, i, j + 1, boardContents, checkTiles)
           + countTiles(WIDTH, HEIGHT, i, j - 1, boardContents, checkTiles)
           + 1;    
}

I cannot for the life of me figure out what's going out of bounds. I even separated the decision structure in countTiles() to make sure that it wouldn't check either array if the number was out of bounds.

Any ideas?

Also, if you're wondering what tileCount[8][8] is for, its so that when I have called tileCount() for each tile, I will have a number that is either 0 or the number of white tiles in an area. I plan on using the numbers that aren't 0 to output how many tiles were in each area and how many areas there were.

[LB]

Why do you pass width and height to functions that take arrays with predefined sizes?

[ResidentBiscuit]

I bet you'll find it pretty easily stepping through with a debugger.

[bwilfong3]

I suppose just to be safe.. my instructor mentioned using constants for the sizes although I don't see much use in them if the array size is already declared. Could this be the root of my problem?

[bwilfong3]

I am using cygwin with nano editor.. is there a debugger that comes prepackaged or something else I could install?

[LB]

Do you have access to gdb?

[bwilfong3]

Yes, I am actually looking through it currently.

This is what I got

Program received signal SIGSEGV, Segmentation fault.
0x00000001004013ec in countTiles (WIDTH=0, HEIGHT=0, i=0, j=0, boardContents=0x23a900,
    checkTiles=0x23a940) at prog1.cpp:84
84      {
(gdb) where
#0  0x00000001004013ec in countTiles (WIDTH=0, HEIGHT=0, i=0, j=0,
    boardContents=0x23a900, checkTiles=0x23a940) at prog1.cpp:84
#1  0x00000001004014af in countTiles (WIDTH=8, HEIGHT=8, i=0, j=4,
    boardContents=0x23a900, checkTiles=0x23a940) at prog1.cpp:98
#2  0x00000001004014dd in countTiles (WIDTH=8, HEIGHT=8, i=1, j=4,
    boardContents=0x23a900, checkTiles=0x23a940) at prog1.cpp:99
#3  0x00000001004014af in countTiles (WIDTH=8, HEIGHT=8, i=0, j=4,
    boardContents=0x23a900, checkTiles=0x23a940) at prog1.cpp:98
#4  0x00000001004014dd in countTiles (WIDTH=8, HEIGHT=8, i=1, j=4,
    boardContents=0x23a900, checkTiles=0x23a940) at prog1.cpp:99
#5  0x00000001004014af in countTiles (WIDTH=8, HEIGHT=8, i=0, j=4,
    boardContents=0x23a900, checkTiles=0x23a940) at prog1.cpp:98
#6  0x00000001004014dd in countTiles (WIDTH=8, HEIGHT=8, i=1, j=4,
    boardContents=0x23a900, checkTiles=0x23a940) at prog1.cpp:99
#7  0x00000001004014af in countTiles (WIDTH=8, HEIGHT=8, i=0, j=4,
    boardContents=0x23a900, checkTiles=0x23a940) at prog1.cpp:98
#8  0x00000001004014dd in countTiles (WIDTH=8, HEIGHT=8, i=1, j=4,
    boardContents=0x23a900, checkTiles=0x23a940) at prog1.cpp:99
#9  0x00000001004014af in countTiles (WIDTH=8, HEIGHT=8, i=0, j=4,
    boardContents=0x23a900, checkTiles=0x23a940) at prog1.cpp:98
#10 0x00000001004014dd in countTiles (WIDTH=8, HEIGHT=8, i=1, j=4,
    boardContents=0x23a900, checkTiles=0x23a940) at prog1.cpp:99
#11 0x00000001004014af in countTiles (WIDTH=8, HEIGHT=8, i=0, j=4,
    boardContents=0x23a900, checkTiles=0x23a940) at prog1.cpp:98
#12 0x00000001004014dd in countTiles (WIDTH=8, HEIGHT=8, i=1, j=4,
    boardContents=0x23a900, checkTiles=0x23a940) at prog1.cpp:99
#13 0x00000001004014af in countTiles (WIDTH=8, HEIGHT=8, i=0, j=4,
    boardContents=0x23a900, checkTiles=0x23a940) at prog1.cpp:98
#14 0x00000001004014dd in countTiles (WIDTH=8, HEIGHT=8, i=1, j=4,
    boardContents=0x23a900, checkTiles=0x23a940) at prog1.cpp:99
#15 0x00000001004014af in countTiles (WIDTH=8, HEIGHT=8, i=0, j=4,
    boardContents=0x23a900, checkTiles=0x23a940) at prog1.cpp:98
#16 0x00000001004014dd in countTiles (WIDTH=8, HEIGHT=8, i=1, j=4,
    boardContents=0x23a900, checkTiles=0x23a940) at prog1.cpp:99
#17 0x00000001004014af in countTiles (WIDTH=8, HEIGHT=8, i=0, j=4,
    boardContents=0x23a900, checkTiles=0x23a940) at prog1.cpp:98
#18 0x00000001004014dd in countTiles (WIDTH=8, HEIGHT=8, i=1, j=4,
    boardContents=0x23a900, checkTiles=0x23a940) at prog1.cpp:99
#19 0x00000001004014af in countTiles (WIDTH=8, HEIGHT=8, i=0, j=4,
    boardContents=0x23a900, checkTiles=0x23a940) at prog1.cpp:98
#20 0x00000001004014dd in countTiles (WIDTH=8, HEIGHT=8, i=1, j=4,
    boardContents=0x23a900, checkTiles=0x23a940) at prog1.cpp:99
#21 0x00000001004014af in countTiles (WIDTH=8, HEIGHT=8, i=0, j=4,
    boardContents=0x23a900, checkTiles=0x23a940) at prog1.cpp:98
#22 0x00000001004014dd in countTiles (WIDTH=8, HEIGHT=8, i=1, j=4,
    boardContents=0x23a900, checkTiles=0x23a940) at prog1.cpp:99
#23 0x00000001004014af in countTiles (WIDTH=8, HEIGHT=8, i=0, j=4,
    boardContents=0x23a900, checkTiles=0x23a940) at prog1.cpp:98
#24 0x00000001004014dd in countTiles (WIDTH=8, HEIGHT=8, i=1, j=4,
    boardContents=0x23a900, checkTiles=0x23a940) at prog1.cpp:99
#25 0x00000001004014af in countTiles (WIDTH=8, HEIGHT=8, i=0, j=4,
    boardContents=0x23a900, checkTiles=0x23a940) at prog1.cpp:98
#26 0x00000001004014dd in countTiles (WIDTH=8, HEIGHT=8, i=1, j=4,
    boardContents=0x23a900, checkTiles=0x23a940) at prog1.cpp:99
#27 0x00000001004014af in countTiles (WIDTH=8, HEIGHT=8, i=0, j=4,
    boardContents=0x23a900, checkTiles=0x23a940) at prog1.cpp:98

Edit: I have never used a debugger before, so I'm not entirely sure what I'm looking at here..

[LB]

Think about lines 92 and 94. Think very hard about that minus symbol.

[bwilfong3]

Hmm... I understand that if i or j = 0 then the index would be at -1 (in lines 92 and 94) and it would be out of bounds.. but isn't this fixed by my outOfBounds flag? It should just return 0 and not do any more comparisons using the -1, right?

[MiiNiPaa]

It is not he minus that is the problem here, it is line 31 that is misplaced (also gdb did point to the problem: look at the parameters function got called)

[bwilfong3]

Even in removing line 31, I still get a seg fault. Very perplexing..

[MiiNiPaa]

I never said that it is not needed. It is just placed in wrong place.
Imagine what happens if you call your function with parameters 7,0.
First it evaluates itself then calls function with parameters 8,0. It immediatly returns because 8 is not valid index.
Then first function calls another function with parameters 6,0
It evaluates and calls third function with parameter 7,0
Repeat.
Now you have infinite recursion. As soon as stack overflows, you will get segmentation fault.

You need to mark current cell as visited before calling other functions recursively.

[LB]

MiiNiPaa did not mean that line 31 should not exist, rather they meant it should be somewhere else in the current code.

[bwilfong3]

You guys are seriously the best. I am extremely grateful for you help!!!