int *dynArr(int* arr, int n, int isEven) {
    int count = 0;
    int* t = (int*)calloc(n, sizeof(int));
    assert(t);
    if (isEven == 1) {
        for (int i = 0; i < n; i  ) {
            if (arr[i] % 2 == 0) {
                t[count  ] = arr[i];
            }
        }
    }
    t = (int*)realloc(*t, count * sizeof(int));
    return t;
}

void main() {
    int a[] = { 1,8,3,6,11 };
    int n = sizeof(a) / sizeof(int);
    int isEven = 1;
    int* arr = dynArr(a, n, isEven);
    for (int i = 0; i < n; i  ) {
        printf("%d", arr[i]);
    }
}

The problem is when I'm returning the array I don't get any output, When I'm debugging I get this error: "Unhandled exception at 0x7A08B54D (ucrtbased.dll) in homelab8.exe: 0xC0000005: Access violation reading location 0x00000004." Someone have an idea how do I fix this?

CodePudding user response：

First of all, you are passing a bad parameter to realloc. This would easily have been caught had you been using your compiler's warnings.

The other major issue is that you are accessing n elements of the array pointed by arr, but it doesn't have n elements.

Since you have two values to return, you will need to return through arguments (or return a struct).

// Returns 0 on success.
// Returns -1 and sets errno on error.
int filter_even_or_odd(
    int **filtered_arr_ptr,  // The address of a variable that accepts output.
    size_t *filtered_n_ptr,  // The address of a variable that accepts output.
    int *arr,
    size_t n,
    int keep_even            // Keep even or keep odd?
) {
    size_t filtered_n = 0;
    int *filtered_arr = malloc( sizeof(int) * n );
    if (!filtered_arr)
        return -1;

    int to_keep = keep_even ? 0 : 1;
    for ( size_t i = 0; i < n; i   ) {
        if ( arr[i] % 2 == to_keep ) {
            filtered_arr[ filtered_n   ] = arr[i];
        }
    }

    int *tmp = realloc( filtered_arr, sizeof(int) * filtered_n );
    if (tmp)
        filtered_arr = tmp;

    *filtered_arr_ptr = filtered_arr;
    *filtered_n_ptr   = filtered_n;
    return 0;
}