Re: Get the type of a PV in C++ API

[Michael Davidsaver via Tech-talk <tech-talk at aps.anl.gov>]

On 11/2/23 04:45, Eusebio Naif Al-Soliman Fuentes via Tech-talk wrote:

Hello everybody.

 

I have a small question. In the pvaClient library for C++ (https://docs.epics-controls.org/projects/pvaclient-cpp/en/latest/) there are many examples to get the value and other fields of a PV.

 

However, in order to get the value as a double, like in this example https://github.com/epics-rip/exampleCPP/blob/master/exampleClient/src/examplePvaClientGet.cpp,

Is should point out that this URL is in the "epics-rip" organization, which we use as a final resting place for abandoned code.  Not something I would recommend as a starting point for a new development.

you have to previously know that the PV value is a double. Is there any method to get the type (int, long, double...) of the value field? Something like ->getType().

This was a common pain point in early versions of pvDataCPP API.  Certainly for me, which I why I extended the "intermediate" interface classes PVScalar and PVScalarArray with the getAs() and putFrom() methods to attempt some conversion.  Of course to use these, you will still need to check if a field as a scalar or array of scalars.  (as opposed to a union, sub-structure, variant, or arrays of these same)

Another common "gotcha" to watch out when looking through these obsolete examples are calls to getSubField() which do not check for a returned NULL  An alternate form getSubFieldT() exists which throws an exception instead.

With PVXS, I tried to design the API to avoid these common mistakes and others.

For a longer discussion, see:

https://mdavidsaver.github.io/pvxs/overview.html#comparison-with-pvdatacpp

 

Thanks in advance.

--

Saludos/Best regards

University of Granada  

Eusebio Naif Al-Soliman Fuentes
MSc. Data Science and Computer Engineering

eunaif at correo.ugr.es