Create 2D array by passing pointer to function in c - c

Question

So I read dozens of examples of passing an 2D array pointer to function to get/change values of that array in function. But is it possible to create (allocate memory) inside the function. Something like this:
#include <stdio.h>
void createArr(int** arrPtr, int x, int y);
int main() {
int x, y; //Dimension
int i, j; //Loop indexes
int** arr; //2D array pointer
arr = NULL;
x=3;
y=4;
createArr(arr, x, y);
for (i = 0; i < x; ++i) {
for (j = 0; j < y; ++j) {
printf("%d\n", arr[i][j]);
}
printf("\n");
}
_getch();
}
void createArr(int** arrPtr, int x, int y) {
int i, j; //Loop indexes
arrPtr = malloc(x*sizeof(int*));
for (i = 0; i < x; ++i)
arrPtr[i] = malloc(y*sizeof(int));
for (i = 0; i < x; ++i) {
for (j = 0; j < y; ++j) {
arrPtr[i][j] = i + j;
}
}
}

Answer 1

Forget about pointer-to-pointers. They have nothing to do with 2D arrays.
How to do it correctly: How do I correctly set up, access, and free a multidimensional array in C?.
One of many reasons why it is wrong to use pointer-to-pointer: Why do I need to use type** to point to type*?.
Example of how you could do it properly:
#include <stdio.h>
#include <stdlib.h>
void* create_2D_array (size_t x, size_t y)
{
int (*array)[y] = malloc( sizeof(int[x][y]) );
for (size_t i = 0; i < x; ++i)
{
for (size_t j = 0; j < y; ++j)
{
array[i][j] = (int)(i + j);
}
}
return array;
}
void print_2D_array (size_t x, size_t y, int array[x][y])
{
for (size_t i = 0; i < x; ++i)
{
for (size_t j = 0; j < y; ++j)
{
printf("%d ", array[i][j]);
}
printf("\n");
}
}
int main (void)
{
size_t x = 5;
size_t y = 3;
int (*arr_2D)[y];
arr_2D = create_2D_array(x, y);
print_2D_array(x, y, arr_2D);
free(arr_2D);
return 0;
}

Answer 2

Yes, passing a pointer to int ** (but 3 stars is considered bad style), I suggest to return an allocated variable from your function:
int **createArr(int x, int y)
{
int **arrPtr;
int i, j; //Loop indexes
arrPtr = malloc(x*sizeof(int*));
if (arrPtr == NULL) { /* always check the return of malloc */
perror("malloc");
exit(EXIT_FAILURE);
}
for (i = 0; i < x; ++i) {
arrPtr[i] = malloc(y*sizeof(int));
if (arrPtr[i] == NULL) {
perror("malloc");
exit(EXIT_FAILURE);
}
}
for (i = 0; i < x; ++i) {
for (j = 0; j < y; ++j) {
arrPtr[i][j] = i + j;
}
}
return arrPtr;
}
Call it using:
arr = createArr(x, y);

Answer 3

Yes, an array can be initialized this way. As long as you pass a pointer, the memory address should remain the same. So, if you assign anything to the pointer it will valid.
Think of an a[] as a* pointer to the first element
a [][] will be a** pointer to a pointer of the first element or a pointer to the first array (first row of a table)