[This message was posted by Dale Wilson of Object Computing, Inc <[email protected]> to the "FAST Protocol" discussion forum at http://fixprotocol.org/discuss/46. You can reply to it on-line at http://fixprotocol.org/discuss/read/2f1af198 - PLEASE DO NOT REPLY BY MAIL.]
Hi Hei, > I am trying to understand the presence map better. The presence map bits are only used for fields that might not be on the wire. The combination of field operator and presence attribute determines whether the bit is needed. As Rolf explained, in your example, a field with no operator is ALWAYS on the wire, so no presence map bit is needed. If the string field is optional, and not included in the message it is still encoded on the wire as a null string. Take a look at http://code.google.com/p/quickfast/wiki/FastFieldRules This, along with careful reading of the specification that you can find at http://www.fixprotocol.org/fast should give you the information you need to understand how the presence map bits are used by various combinations of operator and presence attributes. Dale [You can unsubscribe from this discussion group by sending a message to mailto:[email protected]]
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