getting an error while trying to free malloc - c

Question

So I have been tasked from school with writing a function that gets an int size parameter, an array of integers and an int flag, and returns an array of pointers, that holds pointers to the cells of the original int array in a sorted manner (ascending if flag==1, else descending).
I wrote it basically on the principle of merge sort, but for some reason I am getting a runtime error that occurs when the program tries to execute line 123 (free a temp int** array)
any idea why it happens and if its fixable?
#define _CRT_SECURE_NO_WARNINGS
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <stdbool.h>
#define SIZE 100
int **pointerSort(int *arr, unsigned int size, int ascend_flag);
void ptrMerge(int arr[], int start, int mid, int end, int *ptrArr[], int flag);
void pmergeSort(int arr[], int start, int end, int *ptrArr[], int flag);
void main() {
unsigned int size, i;
int arr[SIZE];
int **pointers;
int ascend_flag;
printf("Please enter the number of items:\n");
scanf("%u", &size);
for (i = 0; i < size; i++)
scanf("%d", &arr[i]);
scanf("%d", &ascend_flag);
pointers = pointerSort(arr, size, ascend_flag);
printf("The sorted array:\n"); //Print the sorted array
//printPointers(pointers, size);
for (i = 0; i < size; i++)
printf("d%\t%d", *pointers[i], pointers[i]);
free(pointers);
}
int **pointerSort(int *arr, unsigned int size, int ascend_flag) {
int **sortedArr;
sortedArr = (int**)malloc(size * sizeof(int*));
pmergeSort(arr, 0, size - 1, sortedArr, ascend_flag);
return sortedArr;
}
void pmergeSort(int arr[], int start, int end, int *ptrArr[], int flag) {
if (start < end) {
int mid = (start + end) / 2;
pmergeSort(arr, start, mid, ptrArr, flag);
pmergeSort(arr, mid + 1, end, ptrArr, flag);
ptrMerge(arr, start, mid, end, ptrArr, flag);
}
}
void ptrMerge(int arr[], int start, int mid, int end, int *ptrArr[], int flag) {
int i, k = 0;
int p = start, q = mid + 1;
int **tempArr;
tempArr = (int**)malloc((end - start + 1) * sizeof(int*));
for (i = start; i <= end; i++) {
if (arr[p] < arr[q]) {
tempArr[k] = &arr[p];
k++;
p++;
} else { //(arr[p] > arr[q])
tempArr[k] = &arr[q];
k++;
q++;
}
}
while (p <= mid) {
tempArr[k] = &arr[p];
k++;
p++;
}
while (q <= end) {
tempArr[k] = &arr[q];
k++;
p++;
}
if (flag == 1) {
for (i = 0; i < k; i++)
ptrArr[start] = tempArr[i];
start++;
}
} else {
for (i = k - 1; i >= start; i--) {
ptrArr[start] = tempArr[i];
start++;
}
}
for (i = 0; i < k; i++)
printf("%x\t%d\n", ptrArr[i], *ptrArr[i]);
printf("\n");
free(tempArr);
}

Answer 1

You get a segmentation fault because the ptrMerge function corrupts the memory by writing past the end of the tempArr allocated array.
The first loop iterates end - start + 1 times, potentially accessing arr beyond the end of the slices.
The loop continues until p >= mid and q >= end, writing to tempArr[k] with k greater or equal to the number of elements allocated with malloc().
The logic is flawed: you compare the elements of arr at offsets p and q instead of indirecting through the array ptrArr.
Here is a modified version:
int **pointerSort(int *arr, int size, int ascend_flag) {
int **sortedArr = (int**)malloc(size * sizeof(int*));
for (int i = 0; i < size; i++) {
sortedArr[i] = &arr[i];
}
pmergeSort(sortedArr, 0, size - 1, ascend_flag);
return sortedArr;
}
void pmergeSort(int *ptrArr[], int start, int end, int flag) {
if (start < end) {
int mid = start + (end - start) / 2;
pmergeSort(ptrArr, start, mid, flag);
pmergeSort(ptrArr, mid + 1, end, flag);
ptrMerge(ptrArr, start, mid, end, flag);
}
}
void ptrMerge(int *ptrArr[], int start, int mid, int end, int flag) {
int i, k, n = end - start + 1;
int p = start, q = mid + 1;
int **tempArr = (int**)malloc(n * sizeof(int*));
for (k = 0; k < n; k++) {
if (p <= mid && (q >= end || *ptrArr[p] <= *ptrArr[q])) {
tempArr[k] = ptrArr[p++];
} else {
tempArr[k] = ptrArr[q++];
}
}
if (flag == 1) {
for (k = 0; k < n; k++)
ptrArr[start + k] = tempArr[k];
}
} else {
for (k = 0; k < n; k++) {
ptrArr[end - k] = tempArr[k];
}
}
free(tempArr);
}
Also note that main() must be defined with a return type int and the loop that prints the values is broken. It should read:
for (i = 0; i < size; i++)
printf("%d\t", *pointers[i]);
printf("\n");

Answer 2

So you should use :
int main(void)
In this while q is never updated so i guess infinite loop?
while (q <= end)
{
tempArr[k] = &arr[q];
k++;
p++;
}
Can you provide me your inputs and output you want?
I have tried your code and i'm not getting your error.