Because I was tired to always answer this question:

Dear rooters,

sometimes, while filling a TTree, I encountered this message:

Error in <TTree::Fill>: Failed filling branch:matches.matches, nbytes=-1

can someone explain me what does it mean? What mistake did I do while creating the code to fill that TTree?

I decided to systematically print this message in addition to the existing message
 This error is symptomatic of a Tree created as a memory-resident Tree
 Instead of doing:
    TTree *T = new TTree(...)
    TFile *f = new TFile(...)
 you should do:
    TFile *f = new TFile(...)
    TTree *T = new TTree(...)


git-svn-id: http://root.cern.ch/svn/root/trunk@15603 27541ba8-7e3a-0410-8455-c3a389f83636