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Subject: Record fields of array type
From: Benjamin Franksen <benjamin.franksen@bessy.de>
To: core-talk@aps.anl.gov
Date: Thu, 19 Jul 2007 17:51:35 +0200
Good Afternoon,

I have now for the <n>th time explained to some desparate EPICS newbie all 
the hoops one has to go through in order to create an array field for a new 
record type. This is starting to get on my nerves, the more so because I 
can't really tell them to go away and RTFM. Because, unfortunately, the 
Fine Manual remains (shamefully?) silent about the fact that this is simply 
not possible in any straight-forward manner, even if your array is supposed 
to be of a fixed size. Instead one has to gather the information necessary 
to work around this limitation from several places in the AppDevGuide 
(Chapter 6.5, Chapter 11.5.7 and Chapter 15.2.3).

I dearly hope that with 3.15 there will be a dbd syntax for creating array 
fields. Ideally there should be a way to specify another field whose value 
at startup time determines the maximum number of elements. Life would be 
almost perfect if in addition the runtime number of elements could be 
specified in a similar way. It could be as simple as just one more 
(possible) property for a field value like, for instance,

field(BLA,DBF_UCHAR) {
	...
	array(NELM,NORD)
}

which might optionally allow a literal number for the first argument (for a 
fixed size array) and where the second argument is optional (for arrays 
that don't change their number of elements at runtime).

This would be a tremendously useful addition and would come at very low 
cost. It is even backward compatible. Frankly, I am amazed that something 
like this hasn't been done a long time ago.

Cheers
Ben
PS: I hope everyone reading the first paraggraph can mentally add the 
missing smileys at the appropriate places themselves.

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