[Trilinos-Users] RCP and loading CrsGraph from HDF5 file

[Bartlett, Roscoe A]

Davood,

What you have will not work and will most likely cause a segfault.

When working with RCP, it is critical that you understand exactly what is going on and how it interacts with the C++ type system.

For a basic introduction on Teuchos::RCP, see:

    http://www.cs.sandia.gov/~rabartl/RefCountPtrBeginnersGuideSAND.pdf

For some more detailed information, see:

    http://www.cs.sandia.gov/~rabartl/rabartl_TUG_RCP_Talk.pdf

Note that all of Trilinos is not updated to use Teuchos::RCP so in cases like with the class EpetraExt::HDF5, you have to be very careful to get them into an RCP correctly.

>From looking at the code in EpetraExt_HDF5.cpp, it seems that this is how you would successfully read into RCP wrapped objects:

    using Teuchos::RCP;
    using Teuchos::rcp;

    HDF5.Open("CRSGraph.h5");

    Epetra_Map *tmpRowMap = 0;
    HDF5.Read("Map", tmpRowMap);
    RCP<Epetra_Map> rowMap = rcp(tmpRowMap);
    tmpRowMap = 0;

    Epetra_CrsGraph *tmpCrsGraph = 0;
    HDF5.Read("Graph", tmpCrsGraph) ;
    RCP<Epetra_CrsGraph> crsGraph = rcp(tmpCrsGraph);
    tmpCrsGraph = 0;

    HDF5.Close();
I have not compiled and tested this code so I don't know if this is 100% correct but it should be very close.

If you look through the documents above and through the file EpetraExt_HDF5.cpp, hopefully you should be able to see what is going on here.

Cheers,

- Ross

P.S.  You should almost never employ a C-style cast like (Epetra *&).  Such an attempt is almost always going to silence the C++ compiler but will result in wrong code that will segfault your program.  In the future, if you are tempted to resort to a C-style cast like this then you need to stop and investigate what is really going on.


---------------------------------------------------------
Dr. Roscoe A. Bartlett
Senior Member of the Technical Staff
Sandia National Laboratories
Phone: (505) 275-6147



________________________________
From: trilinos-users-bounces at software.sandia.gov [mailto:trilinos-users-bounces at software.sandia.gov] On Behalf Of Davood Ansari
Sent: Friday, September 26, 2008 1:45 AM
To: trilinos-users at software.sandia.gov
Subject: [Trilinos-Users] RCP and loading CrsGraph from HDF5 file

Hi all

This should seem a bit dumb.
I am not good at OOp so I put it like this.
In the following piece, I had to use the type cast - (Epetra_Map*&) - or it would not compile.
My intention is to load a EpetraCrsGraph and a Epetra_Map into RCP pointed objects.
Would the following code handle the garbage collection right? Or should I write it differently?
Kindly Advise
Davood


    Teuchos::RCP<Epetra_Map::Epetra_Map> RowMap ;
    Teuchos::RCP<Epetra_CrsGraph::Epetra_CrsGraph> CrsGraph ;

    HDF5.Open("CRSGraph.h5");
    HDF5.Read("Map", (Epetra_Map*&)RowMap) ;
    HDF5.Read("Graph", (Epetra_CrsGraph*&)CrsGraph) ;
    HDF5.Close();


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