Experimental Physics and
Industrial Control System

On Oct 29, 2020, at 10:59 AM, Alfio Rizzo via Tech-talk <tech-talk at aps.anl.gov> wrote:

I was wondering if the the correct way to get the PV aliased name is to look at the .NAME field of its alias.

If I do 

Ø  pvget myalias.NAME

I should get the “real” PV name which the alias point to.

However this start to not be true if the length of the “real” PV name is > 39 chars ( <= 60 )

since the .NAME filed value is truncated to 39 chars (maybe  some limitation on DBR_STRING ?)  

That is indeed the expected way to get the canonical name, and I can use caget's long string support to fetch names that are longer than 39 characters:

woz$ caget this-is-a-very-long-pvname-prefix:BaseVersion.NAME

this-is-a-very-long-pvname-prefix:BaseVersion.NAME this-is-a-very-long-pvname-prefix:BaseV

woz$ caget -S this-is-a-very-long-pvname-prefix:BaseVersion.NAME$

this-is-a-very-long-pvname-prefix:BaseVersion.NAME$ this-is-a-very-long-pvname-prefix:BaseVersion

Unfortunately pvget doesn’t provide any equivalent to the -S flag of caget, and I’m not aware of any functionality in QSRV that can handle long strings properly at the server end (which would be the right place to handle this):

woz$ pvget this-is-a-very-long-pvname-prefix:BaseVersion.NAME

this-is-a-very-long-pvname-prefix:BaseVersion.NAME 2020-10-29 11:11:09.355  this-is-a-very-long-pvname-prefix:BaseV 

woz$ pvget this-is-a-very-long-pvname-prefix:BaseVersion.NAME$

this-is-a-very-long-pvname-prefix:BaseVersion.NAME$ 2020-10-29 11:11:09.355  [116,104,105,115,45,105,115,45,97,45,118,101,114,121,45,108,111,110,103,45,112,118,110,97,109,101,45,112,114,101,102,105,120,58,66,97,115,101,86,101,114,115,105,111,110,0]

There is an issue filed against QSRV for this, but nobody has proposed a good solution yet. Ideas and code contributions welcomed from any C++ developers out there!

- Andrew