RefSeqNum (FIX tag 45)
RefSeqNum (tag 45) is a SeqNum field defined in FIX 4.4, FIX 4.2 and FIX 5.0 SP2. It appears in 2 message types and is required in 1 of them.
At a glance
- Tag
- 45
- Name
- RefSeqNum
- Datatype
- SeqNum (int)
- Dialects
- FIX 4.4, FIX 4.2 and FIX 5.0 SP2
- Messages
- 2
What the specification says
Reference message sequence number
Descriptions are quoted from the FIX Orchestra sources under the Apache 2.0 licence.
A real message using tag 45
| Tag | Field | Wire value | Meaning |
|---|---|---|---|
| 8 | BeginString | FIX.4.4 | |
| 9 | BodyLength | 68 | |
| 35 | MsgType | 3 | Reject |
| 49 | SenderCompID | BOARTEAM | |
| 56 | TargetCompID | COUNTERPARTY | |
| 34 | MsgSeqNum | 2 | |
| 52 | SendingTime | 20240101-12:00:00.000 | |
| 45 | RefSeqNum | 1 | |
| 10 | CheckSum | 142 |
Shown with | separators for readability. On the wire FIX uses SOH (0x01), an invisible control byte — and because BodyLength and CheckSum are computed over the actual bytes, the two forms have different checksums. Both are valid and both decode here.
Generated from the FIX 4.4 dictionary and verified at build time: it parses and validates with no issues. Open the decoder to try your own message.
Where tag 45 appears
Requiredness is a property of the message, not of the field: the same tag can be optional in one message and conditionally required in another.
| Message | MsgType | FIX 4.4 | FIX 4.2 | FIX 5.0 SP2 | Where in the message |
|---|---|---|---|---|---|
| BusinessMessageReject | j | Optional | Optional | Optional | directly on the message body |
| Reject | 3 | Required | Required | Required | directly on the message body |
Wire format
A positive sequence number. Session-level, and monotonic within a session. @boarteam/fix parses the value as a number and reports parse/invalid-int when it does not lex as one; the raw string is kept either way.
Read tag 45 in TypeScript
import { createFixEngine } from "@boarteam/fix";import { dictionary } from "@boarteam/fix-dict-fix44";const fix = createFixEngine(dictionary);const { message, issues } = fix.parse(raw);const field = message.fields[45];field?.name; // "RefSeqNum"field?.raw; // the verbatim wire stringfield?.value; // coerced to a numberOther SeqNum fields
Decode this in your own code
The same engine that produced the decoded example above is an Apache-2.0 npm package with zero runtime dependencies. It runs in Node and in the browser, and parse() returns problems as data instead of throwing.
npm i @boarteam/fix @boarteam/fix-dict-fix44