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<== Date ==> <== Thread ==>

Subject: FW: EPICS Python client application survey
From: <michael.abbott@diamond.ac.uk>
To: <tech-talk@aps.anl.gov>
Date: Thu, 1 Oct 2009 16:59:03 +0100
Sorry, again this was meant to be CC'd to the list.


From: Andrew Johnson [mailto:anj@aps.anl.gov] 
> On Thursday 01 October 2009 05:16:53 Michael Abbott wrote:

> > 3. What happens if I ask for a PV name ending in $ on a pre 
> 14.11 server?
> > In particular, can I safely just hard-wire the special "ends with $ turns
> > into a string" treatment, or is this going to cause backwards
> > compatibility pain?
> 
> Please do *not* look at the PV name in your code, there may 
> be other field modifiers in the future that will also 
> generate a string as a DBF_CHAR array, and existing 
> applications already use waveform records to store long text 
> strings (MEDM and EDM have both supported this for many years).
> 
> You need to decide how to handle the data based on ca_field_type(), 
> ca_element_count() and whether the application is looking for 
> a string or an array of numbers.  Unfortunately the last part 
> is essential, only the application developer knows whether the 
> aSub.VALA field is supposed to hold a printable string or a pixel array.

Huh.  I think you're not going to like my Python channel access solution then.


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