Adding a TMultiGraph to a TMultiGraph

ROOT
1

Hello,

I am a bit confused about adding a TMultiGraph to another.
TMultiGraph::Add(TGraph*) inline documentation explicitly says that once you give TMultiGraph a TGraph, it owns it.
The code of TMultiGraph::Add(TMultiGraph*) seems similar enough to the TGraph* one… so, how should I use this feature? After a

pMGsmall->Add(pGraph); // add a TGraph
pMGbig->Add(pMCsmall); // add a TMultiGraph

who owns pGraph? will deleting pMGsmall and pMGbig try to delete pGraph twice?
Having it clarified in the documentation could also help.
Thank you.

2

Yes you are right, it looks like the graphs might be deleted twice. Have you encounter this problem ?
Do you have a small macro showing it ?

3

No, sorry.
I was still in the design phase (of a 200-lines thing, nothing big), I was pondering my options and this one in particular. When I smelled trouble I freaked out and ran away (with a TObjArray).
So it’s more like thought-coding. My problem was that I could not even figure out how to do the thing correctly.
I have put together this:

TGraph* pGraph = new TGraph(10);
TMultiGraph* pMGsmall = new TMultiGraph("MGSmall", "The small one");
TMultiGraph* pMGbig = new TMultiGraph("MGBig", "The big one");
pMGsmall->Add(pGraph); // fill a multigraph with graphs
pMGbig->Add(pMGsmall); // fill a multigraph with other multigraphs
// ... err... now what? cleaning?
delete pMGsmall;
delete pMGbig;

This explodes (segmentation fault) at the last line, regardless the order of the last two lines (ROOT 5.30/01).
But it might be because I did something stupid in the previous ones.
The backtrace points to TCollection::GarbageCollect(TObject*).

4

Hi,

Yes, the TMultiGraph owns its content and thus you only need one delete:delete pMGbig;

Cheers,
Philippe.