What is an efficient way to get column from multi-dimensional array in C? -

i have 2 structs: array2d (multidimensional) , array (one-dimensional). column type array2d , copy type array.

although code works below, , recognize poor way of getting column array, i'm curious optimizations there might avoid o(n2) algorithm. efficient way column array in c?

bool arr2_getcolumn(array2d *arr, const int column_index, array *returnedarray) {     int x, y;     int = 0;      /* check valid array. */     if (arr->blnisinit != true)         return false;      /* initialize array column's height. */      if (!arr_init(returnedarray, arr->height))         return false;      /* copy on column. */     (y = 0; y < arr->height; y++)     {         (x = 0; x <= column_index; x++)         {             if (x == column_index)             {                  returnedarray->array[i] = arr->array[y * arr->width + x];                 i++;             }          }     }       /* set new size. */     returnedarray->size = arr->height;      return true; } 

get rid of i , x.

for (y = 0; y < arr->height; y++) {     returnedarray->array[y] = arr->array[y * arr->width + column_index]; }