Experimental Physics and
Industrial Control System

Andrew Johnson <[email protected]> · Thu, 15 Nov 2012 11:43:07 -0500

Hi Lewis,

On 2012-11-15 J. Lewis Muir wrote:
> 
> The problem with this logic is that you're thinking of a waveform
> record's VAL field as a C string.  

Sorry, but I'm not.  I understand that waveform records can hold all kinds of 
data, but I'm not asking this to be done for me personally.  Think of my 
recommendation as asking for a safety railing on a cliff-top.

> Another problem with including the NUL byte is that if I fetch a
> waveform record's VAL field from another language, say Java, I now have
> to do extra work by checking to see if the NUL byte is included and
> throw it away if it is; it's a totally bogus character in this context.

You'll have to do that anyway, because if you point your Java client using the 
$ field modifier at an 80-char CALC field or a link address you *will* get a 
Nil byte in it that terminates the string.  With the current code that Nil 
byte may be followed by non-Nil data from previous contents of that field 
(because the field modifier code doesn't support dynamimc sizing yet anyway), 
so code that converts a char array into a non-C string must stop at either the 
first Nil or the end of the array.

Until we added dynamic array sizing CA could only give you ca_element_count() 
characters with Nil values used to fill up the array after the first NORD 
characters.

- Andrew
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Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System