Function array_iterate

src/backend/utils/adt/arrayfuncs.c:4565–4643

* Iterate through the array referenced by 'iterator'. * * As long as there is another element (or slice), return it into * *value / *isnull, and return true. Return false when no more data. */

 * *value / *isnull, and return true.  Return false when no more data.
 */
bool
array_iterate(ArrayIterator iterator, Datum *value, bool *isnull)
{
	/* Done if we have reached the end of the array */
	if (iterator->current_item >= iterator->nitems)
		return false;

	if (iterator->slice_ndim == 0)
	{
		/*
		 * Scalar case: return one element.
		 */
		if (array_get_isnull(iterator->nullbitmap, iterator->current_item++))
		{
			*isnull = true;
			*value = (Datum) 0;
		}
		else
		{
			/* non-NULL, so fetch the individual Datum to return */
			char	   *p = iterator->data_ptr;

			*isnull = false;
			*value = fetch_att(p, iterator->typbyval, iterator->typlen);

			/* Move our data pointer forward to the next element */
			p = att_addlength_pointer(p, iterator->typlen, p);
			p = (char *) att_align_nominal(p, iterator->typalign);
			iterator->data_ptr = p;
		}
	}
	else
	{
		/*
		 * Slice case: build and return an array of the requested size.
		 */
		ArrayType  *result;
		Datum	   *values = iterator->slice_values;
		bool	   *nulls = iterator->slice_nulls;
		char	   *p = iterator->data_ptr;
		int			i;

		for (i = 0; i < iterator->slice_len; i++)
		{
			if (array_get_isnull(iterator->nullbitmap,
								 iterator->current_item++))
			{
				nulls[i] = true;
				values[i] = (Datum) 0;
			}
			else
			{
				nulls[i] = false;
				values[i] = fetch_att(p, iterator->typbyval, iterator->typlen);

				/* Move our data pointer forward to the next element */
				p = att_addlength_pointer(p, iterator->typlen, p);
				p = (char *) att_align_nominal(p, iterator->typalign);