I'm trying to implement a sudoku solver. To do this i am using a struct, shown below, to represent a cell on a sudoku board. I am then declaring a 9x9 array of these structs to represent the board.
cell structure:
struct cell{
char value;
unsigned int possible;
};
then, i declare an array of sctructs as:
struct cell board[9][9];
My problem is, when i try to enter a value into the array, (ie. board[2][2].value = getchar();), sometimes it works, and other times i get this error:
Bus error: 10
I'm not quite sure what this means... How is "Bus error: 10" different from a segmentation fault?
I'm using gcc and just editing in vim. My feelings are, I need to dynamically allocate the memory for this array. Now, I understand how to use malloc to allocate memory for a two dimensional array, something like this:
int ** Array;
Array = (int**) malloc(x_size*sizeof(int*));
for (int i = 0; i < x_size; i++)
Array[i] = (int*) malloc(y_size*sizeof(int));
But I'm having trouble implementing the memory allocation part for a 2 dimensional array of structs.
Would it something like this?
struct cell** board;
board = (struct cell**) malloc(x_size*sizeof(struct cell**));
for(int i=0; i< x_size; i++)
board[i] = (struct cell*) malloc(y_size*sizeof(struct cell));
I'm wary that this " sizeof(struct cell) " is not properly allocating the amount of memory it should be.
Any help would be greatly appreciated! I'm fairly new to C (C++ is my native tongue), I've used embedded C a good amount, but I am trying to better grasp the language as a whole.
Bonus points for detailed\in depth explanations!
Thanks!
EDIT OK, so thanks everyone for the great suggestions, I still haven't implemented any dynamic memory allocation, but, as requested, here is the code that is producing the bus error:
/* only code being used in solver.h*/
29 /* structure to describe a cell */
30 struct cell{
31 int value;
32 unsigned int possible;
33 };
/*solver.c*/
4 #include <ctype.h>
5 #include <stdio.h>
6 #include "solver.h"
7
8
9 struct cell board [9][9];
10
11
12 int main(){
13 initialize_board();
14 print_board();
15 setup_board();
16 print_board();
17 return 0;
18 }
19
20 void print_board(){
21 int i=0, j=0;
22 for(i = 0; i<9; i++){
23 for(j = 0; j<9; j++)
24 printf(" %d",board[i][j].value);
25 printf("\n");
26 }
27 }
28
29 void initialize_board(){
30 int i = 0, j = 0;
31
32 for(i = 0; i<9; i++)
33 for(j = 0; j<9; j++){
34 (board[i][j]).value = 0;
35 (board[i][j]).possible = 0x1FF;
36 }
37 }
38
39 void setup_board(){
40 int row=0, col=0, val = 0;
41 char another = 'Y';
42
43 printf("Board Initial Setup.\nEnter the row and column number of the value to be entered into the board.");
44 printf("\nRow and Column indexes start at one, from top left corner.");
45 while(another == 'Y'){
46 printf("\nRow: ");
47 row = getchar();
48 printf("Column: ");
49 getchar();
50 col = getchar();
51 printf("Value: ");
52 getchar();
53 (board[row-1][[col-1]).value = getchar();
54 printf("Enter another value? (y/n): ");
55 getchar();
56 another = toupper(getchar());
57 getchar();
58 }
59 }
As you can see, i've changed the datatype of value to int to match the getchar() return type. But my code is still producing strange runtime errors/results. For example, in the first iteration of the while loop in setup_board, I can enter say Row:1, Col:1, Value:5, then when i enter 'n' to exit, the board should be printed with 5 in the upper left corner, however this is not the case. The matrix that is printed is still in its state after initialize_board() is called.
Output:
Board Initial Setup.
Enter the row and column number of the value to be entered into the board.
Row and Column indexes start at one, from top left corner.
Row: 1
Column: 1
Value: 4
Enter another value? (y/n): n
0 0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0 0
Also, if i enter other matrix coordinates, thats when i get the Bus Error: output:
Board Initial Setup.
Enter the row and column number of the value to be entered into the board.
Row and Column indexes start at one, from top left corner.
Row: 5
Column: 5
Value: 5
Bus error: 10
Any advice on how to clean up that ugly double getchar() business would be appreciated too.
Thanks everyone!
EDIT NUMBER TWO The problem was with those getchar()'s.... I didn't realize they return an integer ASCII code to represent the numbers instead of the actual numbers themselves. Here is what I've done to fix it:
47 while(another == 'Y'){
48 valid=0;
49 while(!valid){
50 printf("\nRow: ");
51 row = getchar() - '0'; /* convert ASCII character code to actual integer value */
52 getchar(); /*added to remove extra newline character from stdin */
53 printf("Column: ");
54 col = getchar() - '0';
55 getchar(); /*remove \n */
56 printf("Value: ");
57 val = getchar() - '0';
58 getchar(); /*remove \n */
59 if(val >9 || val<1 || col>9 ||col<1 || row>9 || row<1)
61 printf("\nInvalid input, all values must be between 1 and 9, inclusive");
62 else
63 valid = 1;
64 }
65 board[row-1][col-1].value = val;
66 printf("Enter another value? (y/n): ");
67 another = toupper(getchar());
68 getchar(); /*remove \n */
69 }
Thanks to everyone for your help and input, I will be implementing many of the suggestions you've all made and have learned a lot just from this question!
EDIT NUMBER THREE
ONE FINAL QUESTION!
Though my original issue is solved, does anyone have strong opinions or reasoning as to whether or not it would be better to implement the matrix by dynamically allocating the memory?
I figure, I'll leave it as is now since it works, but since the matrix is fairly large, would it be better programming practice to dynamically allocate?
getchar returns a code that represents a character; you have to add code that converts it to a number. Consider, for example, the following code:
printf("\nRow: ");
row = getchar();
printf("Column: ");
getchar();
What happens when the user types "hehe" instead of 1 and 1 that the program expects? The program will get ASCII codes for h and e, assign them to row and col and so access out-of-range array elements.
Actually, the same happens with normal input! The user enters 1, the program gets the ASCII code (49) and performs some memory overrun:
board[49-1][49-1].value = 53;
To fix this, convert character codes to numbers:
if (row >= '1' && row <= '9')
row -= '0'; // a common C hack for converting a character-code to a number
else
printf("Bad input"); // not a proper error handling, just an example
col -= '0'; // 1 line for brevity; you must do the same code as above
value = getchar();
value -= '0'; // same as above
board[row-1][col-1].value = value;