Thank you, Wolfgang! This is exactly what I am looking for. I don‘t need to 
access the pointer from outside, I am trying to extend the p4est-interface 
itself.

Best,
Konrad

On Friday, May 14, 2021 at 12:42:48 AM UTC+2 Wolfgang Bangerth wrote:

> On 5/13/21 3:05 PM, Konrad Simon wrote:
> > 
> > I am currently writing an interface to some p4est functions. The 
> structure of 
> > p4est makes it often necessary to pass data around through a user 
> pointer of 
> > whatever type (void*). When creating a new triangulation this pointer is 
> set 
> > to „this“ (the triangulation itself), see for example
> > 
> > 
> https://www.dealii.org/current/doxygen/deal.II/distributed_2tria_8cc_source.html#l2989
>  
> > <
> https://nam10.safelinks.protection.outlook.com/?url=https%3A%2F%2Fwww.dealii.org%2Fcurrent%2Fdoxygen%2Fdeal.II%2Fdistributed_2tria_8cc_source.html%23l2989&data=04%7C01%7CWolfgang.Bangerth%40colostate.edu%7Cb4cadd28da84445fd29308d91652e2c3%7Cafb58802ff7a4bb1ab21367ff2ecfc8b%7C0%7C0%7C637565367510208994%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C1000&sdata=v2G100jGfI6SbGwV35raSFjMxfnJMJurP2F2qAc61Ls%3D&reserved=0
> >
> > 
> > Is this pointer used in other interfaces somehow? p4est itself does not 
> touch 
> > it so I am wondering if I can reset it to anything I‘d like.
>
> Konrad,
> we use this user pointer in many of the functions that are called back 
> from 
> p4est. Take a look at
> RefineAndCoarsenList<dim, spacedim>::refine_callback
> for example (line 761 of the file), and many other functions that you can 
> find 
> by searching for
> forest->user_pointer
> in this file.
>
> We consider the p4est forest object as internal to the p::d::T class, so I 
> would expect that you can't access it, or expect that you can use any of 
> its 
> content for anything other than what the p::d::T class does with it.
>
> Best
> W.
>
>
> -- 
> ------------------------------------------------------------------------
> Wolfgang Bangerth email: [email protected]
> www: http://www.math.colostate.edu/~bangerth/
>
>

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