Re: Get sub field of Union

["Shen, Guobao via Core-talk" <core-talk@aps.anl.gov>]

The union is what we are using for our fast DAQ data from FPGA.
Our engineers designed the structure that format, and it has similar structure with AD image.
We do not use a union containing a structure, which might complicate the system.

In this case, you mean what I got is what I should expect. Right?

On 3/21/19, 1:20 PM, "Michael Davidsaver" <mdavidsaver@gmail.com> wrote:

    On 3/21/19 8:43 AM, Shen, Guobao via Core-talk wrote:
    > Hi Core member,
    > 
    > Does anyone have experienced to read sub field of a Union structure?
    
    What you are showing looks like a discriminating/tagged union.
    This is quite different to having a union containing a structure,
    which is maybe what you expect?
    
    
    > For example, I have a record:
    > 
    > $ pvinfo Test:Data
    > 
    > …
    > 
    > structure
    > 
    >     uint ArrayId
    > 
    >     double[] Time
    > 
    >     union value
    > 
    >         float[] data1
    > 
    >         double[] data2
    > 
    >  
    > 
    > If I use
    > 
    > $ pvget -r value Test:Data
    > 
    > Test:Data
    > 
    > structure
    > 
    >     union value
    > 
    >         float[]  [-0.034794,-0.0417011, …]
    > 
    >  
    > 
    > But if I do it with:
    > 
    > $ pvget -r value.data1 Test:Data
    > 
    >  
    > 
    > I got an error on my client like
    > 
    > [Test: Data] failed to create channel get: Status [type=FATAL, message=std::bad_alloc]
    > 
    >  
    > 
    > Is that a right way to use it for union?
    > 
    >  
    > 
    > Thanks,
    > 
    > Guobao
    >