|
FAST Protocol
< Previous Next >
Re: Presence Map
Dale Wilson / Object Computing, Inc
11 Jan 2010 11:48AM ET 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
Re: Presence Map
Dale Wilson / Object Computing, Inc 11 Jan 2010 11:48AM ET
|
