otxn_slot

Summary. Load the entire originating transaction into a slot, so its subfields and arrays can be navigated with the slot APIs.

Signature.

int64_t otxn_slot(uint32_t slot_no);

Parameters.

Name	Type	Description
slot_no	uint32_t	Target slot number (1..255), or 0 to auto-allocate a free slot.

Return value. Returns the slot number the transaction was loaded into (the same value you passed, or the auto-allocated one when you passed 0). Errors: INVALID_ARGUMENT (-7) if slot_no is greater than max_slots (255); NO_FREE_SLOTS (-6) if slot_no == 0 and no slot is free.

Common failure patterns.

• Passing a slot_no above 255 → INVALID_ARGUMENT.
• Requesting auto-allocation (0) when all 255 slots are in use → NO_FREE_SLOTS.

Caveats / notes.

• Loading into an occupied slot_no overwrites it. Pass 0 and use the returned number to avoid clobbering an existing slot.
• Once slotted, use slot_subfield / slot_subarray to reach nested fields (e.g. an amount or a memo), slot_float to read an amount as XFL, and slot to copy raw bytes out. This is the preferred route for structured or nested access, versus the flat serialization from otxn_field.
• During a failed-emit callback the slotted object is the emitted transaction (same emitFailure rule as the rest of the family).

Minimal example.

int64_t slot_no = otxn_slot(0);   // auto-allocate a slot for the whole txn

Practical example.

// Load the originating transaction, expand its sfAmount subfield, and read
// it as an XFL floating value.
#define sfAmount ((6U << 16U) + 1U)
int64_t txn = otxn_slot(0);
if (txn < 0)
    rollback(SBUF("could not slot otxn"), __LINE__);

if (slot_subfield(txn, sfAmount, 1) != 1)
    rollback(SBUF("no Amount field"), __LINE__);

int64_t amt = slot_float(1);      // XFL value of the amount
accept(SBUF("read amount"), 0);

Related APIs. slot_subfield, slot_float, slot, meta_slot, otxn_field.