RE: A question about TClonesArray

From: Philippe Canal <pcanal_at_fnal.gov>
Date: Thu, 10 Nov 2005 11:36:47 -0600

 

> theData->Clear(); //Clear the TClonesArray, Does this mean the orignal

This simply tell the TClonesArray that it is empty (however it kepts holding the memory it has allocated so far for later reuse.

> //AddrAt(Int_t) just return the Object* in specified slot, so it
> //does nothing here?

No. It actually set the entry as valid (if it was not already) and should (if it is the first time) use:

   new (theData->AddrAt(entry)) MyClass(...); to properly initizalize it.

Cheers,
Philippe.

-----Original Message-----
From: owner-roottalk_at_pcroot.cern.ch [mailto:owner-roottalk_at_pcroot.cern.ch] On Behalf Of Datao Gong
Sent: Thursday, November 10, 2005 10:32 AM Cc: roottalk_at_pcroot.cern.ch
Subject: [ROOT] A question about TClonesArray

Hi, Guys,
When i read a piece of code writte by other people, i think i might misunderstand something about TClonesArray.

This code increase TClonesArray size on demand. It should not change the content which has been filled in.

My question are embeded in the comments.

   if(theMaxSize < 10) theMaxSize = 10;

   else if(theMaxSize < 30) theMaxSize = 30;
   else if(theMaxSize < 100) theMaxSize = 100;
   else if(theMaxSize < 250) theMaxSize = 250;

   else theMaxSize *= 2;

   theData->ExpandCreateFast(theMaxSize); //increase Size

   theData->Clear(); //Clear the TClonesArray, Does this mean the orignal

                     //infomation are lost after that!?

   for(Int_t entry = 0; entry < theSize; ++entry) theData->AddrAt(entry);
 	//AddrAt(Int_t) just return the Object* in specified slot, so it
 	//does nothing here?

BTW, this code works. But i just do not know why.

Thanks,

Datao Received on Thu Nov 10 2005 - 18:43:40 MET