Getting heap overflow even on deallocating memory - c

Question

I am trying to solve the n-queen problem on leetcode. But it is giving heap overflow error on leetcode.
But on my computer when I give single input it give correct answer but on giving input multiple times it gives segmentation fault: 11 error.
And when I don't print the complete chess board. Just printing the number of different possible solution. Then also it works fine.
#include <stdio.h>
#include <stdlib.h>
#define bool int
#define true 1
#define false 0
//checking positioned queens
bool checkPlacedQueens(char **board, int queeni, int queenj, int n) {
int i=queeni;
int j=queenj;
//checking complete row
for(int i=queeni; i>=0; i--) {
if(board[i][j] == 'Q')
return false;
}
i=queeni;
j=queenj-1;
//checking left diagonal
while(i>=0 && j>=0) {
if(board[i--][j--] == 'Q')
return false;
}
i=queeni;
j=queenj+1;
//checking right diagonal
while(i>=0 && j<=n) {
if(board[i--][j++] == 'Q')
return false;
}
return true;
}
char ***placeQueens(char **board, int queenI, int n, int *returnSize, char ****result) {
//all queens are on their correct position
if(queenI == n) {
(*returnSize)++;
/*
reallocating the memory to save all the outputs in 3D
array
*/
(*result) = (char ***) realloc(*result, sizeof(char **)*(*returnSize));
(*result)[*returnSize-1] = (char **)malloc(sizeof(char *)*n);
for(int i=0; i<n; i++) {
(*result)[*returnSize-1][i] = (char *)malloc(sizeof(char)*n);
}
for(int i=0; i<n; i++) {
for(int j=0; j<n; j++) {
(*result)[*returnSize-1][i][j] = board[i][j];
}
}
return *result;
}//if
for(int j=0; j<n; ++j) {
char save = board[queenI][j];
board[queenI][j] = 'Q';
if(checkPlacedQueens(board, queenI-1, j, n)) {
placeQueens(board, queenI+1, n, returnSize, result);
}
board[queenI][j] = save;
}//for Loop
return *result;
}//function
char *** solveNQueens(int n, int* returnSize) {
char **board;
char ***result = (char ***)malloc(sizeof(char **));
board = (char **)malloc(sizeof(char *)*n);
for(int i=0; i<n; i++) {
board[i] = (char *)malloc(sizeof(char)*n);
}
for(int i=0; i<n; i++) {
for(int j=0; j<n; j++) {
board[i][j] = '.';
}
}
placeQueens(board, 0, n, returnSize, &result);
for(int i=0; i<n; i++)
free(board[i]);
free(board);
return result;
}//char
int main(void) {
int returnSize=0;
int n=4;
char ***arr;
while(n<10) {
arr = solveNQueens(n, &returnSize);
for(int i=0; i<returnSize; ++i) {
for(int j=0; j<n; j++) {
for(int k=0; k<n; k++) {
printf("%c", arr[i][j][k]);
}
printf("\n");
}
printf("\n");
}
printf("\n\n\n");
for(int i=0; i<returnSize; ++i) {
for(int j=0; j<n; j++) {
free(arr[i][j]);
}
free(arr[i]);
}
free(arr);
arr=NULL;
n++;
}
}//main

Answer 1

Yoor code has an out-of-bounds read illegal memory access. A live test of it is here segfault diagnoser,
The following is the diagnostic message of the out-of-bounds read.
====== Start of Stensal DTS message == (56.133) == copy start here ======
[out-of-bounds read] is detected by Stensal DTS.
Continuing execution can cause undefined behavior, abort!
+--------------------------------------------------------------------------+
| Reading 1 bytes from 0x80c5054 will read undefined values.
|
| The object to-be-read (start:0x80c5050, size:4 bytes) is allocated at
| file:/prog.c::83, 28
|
| 0x80c5050 0x80c5053
| +------------------------+
| | the object to-be-read |......
| +------------------------+
| ^~~~~~~~~~
| the read starts at 0x80c5054 that is right after the object end.
|
| Stack trace (most recent call first) of the read.
| [1] file:/prog.c::31, 12
| [2] file:/prog.c::67, 12
| [3] file:/prog.c::68, 13
| [4] file:/prog.c::92, 5
| [5] file:/prog.c::107, 15
| [6] [libc-start-main]
+--------------------------------------------------------------------------+
======= End of Stensal DTS message =============== copy end here =========

Answer 2

The problem is that your are not resetting the value of returnSize each time you re-call the solveNQueens function.
The following is a working code:
#include <stdio.h>
#include <stdlib.h>
#define bool int
#define true 1
#define false 0
//checking positioned queens
bool checkPlacedQueens(char **board, int queeni, int queenj, int n) {
int i=queeni;
int j=queenj;
//checking complete row
for(int i=queeni; i>=0; i--) {
if(board[i][j] == 'Q')
return false;
}
i=queeni;
j=queenj-1;
//checking left diagonal
while(i>=0 && j>=0) {
if(board[i--][j--] == 'Q')
return false;
}
i=queeni;
j=queenj+1;
//checking right diagonal
while(i>=0 && j<=n) {
if(board[i--][j++] == 'Q')
return false;
}
return true;
}
char ***placeQueens(char **board, int queenI, int n, int *returnSize, char ****result) {
//all queens are on their correct position
if(queenI == n) {
(*returnSize)++;
/*
reallocating the memory to save all the outputs in 3D
array
*/
(*result) = (char ***) realloc(*result, sizeof(char **)*(*returnSize));
(*result)[*returnSize-1] = (char **)malloc(sizeof(char *)*n);
for(int i=0; i<n; i++) {
(*result)[*returnSize-1][i] = (char *)malloc(sizeof(char)*n);
}
for(int i=0; i<n; i++) {
for(int j=0; j<n; j++) {
(*result)[*returnSize-1][i][j] = board[i][j];
}
}
return *result;
}//if
for(int j=0; j<n; ++j) {
char save = board[queenI][j];
board[queenI][j] = 'Q';
if(checkPlacedQueens(board, queenI-1, j, n)) {
placeQueens(board, queenI+1, n, returnSize, result);
}
board[queenI][j] = save;
}//for Loop
return *result;
}//function
char *** solveNQueens(int n, int* returnSize) {
char **board;
char ***result = (char ***)malloc(sizeof(char **));
board = (char **)malloc(sizeof(char *)*n);
for(int i=0; i<n; i++) {
board[i] = (char *)malloc(sizeof(char)*n);
}
for(int i=0; i<n; i++) {
for(int j=0; j<n; j++) {
board[i][j] = '.';
}
}
placeQueens(board, 0, n, returnSize, &result);
for(int i=0; i<n; i++)
free(board[i]);
free(board);
return result;
}//char
int main(void) {
int n=4;
char ***arr;
while(n<10) {
// Reset the value of returnSize
int returnSize=0;
arr = solveNQueens(n, &returnSize);
for(int i=0; i<returnSize; ++i) {
for(int j=0; j<n; j++) {
for(int k=0; k<n; k++) {
printf("%c", arr[i][j][k]);
}
printf("\n");
}
printf("\n");
}
printf("\n\n\n");
for(int i=0; i<returnSize; ++i) {
for(int j=0; j<n; j++) {
free(arr[i][j]);
}
free(arr[i]);
}
free(arr);
arr=NULL;
n++;
}
}//main