Backward compatibility

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Imported from previous forum

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Are FIX versions backward compatible?

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[ original email was from Ryan Pierce - rpierce@taltrade.com ]
> Are FIX versions backward compatible?

Absolutely not. There’s no concept of forwards or backwards compatibility across FIX versions. In many cases, a message valid in one FIX version would be invalid in any other FIX version, even if the BeginString were changed.

So, in other words, a FIX 4.4 system isn’t going to accept FIX 4.1 orders magically.

However, coding software that handles multiple FIX versions isn’t that difficult. Generally, changes made are cumulative; something added in one version will stay around in future versions. I personally choose to represent FIX version as an integer, and define an enumeration for it, so I can do comparisons.

I.e.

if ( FIXVersion < FIX_VERSION_4_1 )
Send OrdStatus
else
Send ExecType and OrdStatus

if ( FIXVersion >= FIX_VERSION_4_1 )
Send LeavesQty on execution reports

etc.