Why am i getting error in function addRandomNumbers? - c

Question

I am getting an error in addRandomNumbers(). Maybe I didn't correctly allocate memory dynamically? I really have no idea what I did wrong.
The error is:
'Exception thrown: read access violation. _array was 0x1110112.'
Here is my code:
#define _CRT_SECURE_NO_WARNINGS
#include <stdio.h>
#include <stdlib.h>
#include <time.h>
void allocateArray(int** _array, int row, int col) {
_array = (int**)malloc(sizeof(int*) * row);
for (int i = 0; i < row; i++)
_array[i] = (int*)malloc(sizeof(int) * col);
}
void addRandomNumbers(int** _array, int row, int col) {
for (int i = 0; i < row; i++) {
for (int j = 0; j < col; j++) {
_array[i][j] = rand() % 10;
}
}
}
void print(int** _array, int row, int col) {
for (int i = 0; i < row; i++) {
for (int j = 0; j < col; j++) {
printf("%d ", _array[i][j]);
}
printf("\n");
}
}
int main() {
srand((unsigned)time(NULL));
int** _array = NULL;
allocateArray(_array, 5, 5);
addRandomNumbers(_array, 5, 5);
print(_array, 5, 5);
return 0;
}

Answer 1

You're passing _array to the allocateArray function by value, so any changes to the corresponding parameter aren't reflected in the variable in the main function. This means that _array is still NULL when you pass it to addRandomNumbers.
Change allocateArray to return the allocated pointer:
int **allocateArray(int row, int col) {
int **_array = malloc(sizeof(int*) * row);
for (int i = 0; i < row; i++) {
_array[i] = malloc(sizeof(int) * col);
}
return _array;
}
Then assign the return value back to _array:
_array = allocateArray(5, 5);
Alternately, you can change the parameter type to int *** and dereference when using it:
void allocateArray(int ***_array, int row, int col) {
*_array = malloc(sizeof(int*) * row);
for (int i = 0; i < row; i++) {
(*_array)[i] = malloc(sizeof(int) * col);
}
}
And pass the address of the variable in main:
allocateArray(&_array, 5, 5);

Answer 2

I'm assuming you're running into a segmentation fault because that's the error I receive on my machine by running this code.
I think the issue is with allocateArray(), not addRandomNumbers(). addRandomNumbers() is unable to write to the array because the array was not allocated properly. Try this instead:
void allocateArray(int ***_array, int row, int col) {
*_array = (int **)malloc(row * sizeof(int *));
for (int i = 0; i < row; ++i) {
(*_array)[i] = (int *)malloc(col * sizeof(int));
}
}
Likewise, to free the memory, try:
void freeArray(int **_array, int row) {
for (int i = 0; i < row; ++i) {
free(arr[row]);
}
free(arr);
}