slot_subarray

Summary. Extract an array element of a slotted array into a (new or specified) slot.

Signature.

int64_t slot_subarray(uint32_t parent_slot, uint32_t array_id, uint32_t new_slot);

Parameters.

Name	Type	Description
parent_slot	uint32_t	Slot holding an STI_ARRAY.
array_id	uint32_t	Zero-based index of the element to extract.
new_slot	uint32_t	Destination slot, or 0 to allocate a free slot.

Return value. Returns the destination slot number on success. Errors: DOESNT_EXIST (-5) if the parent is empty or array_id is out of range; INTERNAL_ERROR (-2) if corrupt; NOT_AN_ARRAY (-22) if the parent is not an array; INVALID_ARGUMENT (-7) if new_slot exceeds max_slots; NO_FREE_SLOTS (-6) if new_slot == 0 and none are free.

Common failure patterns.

• An array_id beyond the element count → DOESNT_EXIST.
• Calling it on a non-array slot → NOT_AN_ARRAY.

Caveats / notes.

• Use slot_count to get the valid index range first.
• An extracted element may be an object or a leaf field. Use slot_subfield only when the selected element is an object.

Minimal example.

uint32_t elem = slot_subarray(memos_slot, 0, 0);

Practical example.

// Read the first Memo's MemoData from the originating transaction.
int64_t txn = otxn_slot(0);
int64_t memos = slot_subfield(txn, sfMemos, 0);
if (memos > 0 && slot_count(memos) > 0)
{
    uint32_t memo0 = slot_subarray(memos, 0, 0);
    uint32_t memo  = slot_subfield(memo0, sfMemo, 0);
    uint32_t data  = slot_subfield(memo, sfMemoData, 0);
    uint8_t buf[256];
    int64_t n = slot((uint32_t)buf, sizeof(buf), data);
    // ... use buf[0..n) ...
}
accept(SBUF("ok"), 0);

Related APIs. slot_count, slot_subfield.