Calling same function, how to avoid memory leaks in TH1

ROOT
1

In a subroutine, I create the following subroutine:

then fill it:

and then draw it:

However, I want to call this subroutine twice for different data, and hence in both cases create, fill and draw the histogram, with different data.
When I do it as above, the 2nd calling of the subroutine I get the warning:
Warning in TROOT::Append: Replacing existing TH1: h1 (Potential memory leak).

So, at the end of the subroutine, I call “delete h1”.
But now, it will delete the histograms as plotted on the canvas. (And I end up with nothing).

Another way, would be giving different names, according to the data that is called. Like this:

TH2D* h1 = 0; if (first) h1 = new TH2D("h1_1" , title.c_str(), 100, -2.0, 2.0, 100, -2.0, 2.0); // first time called else h1 = new TH2D("h1_2" , title.c_str(), 100, -2.0, 2.0, 100, -2.0, 2.0); // second time called

But of course, now, I will have to do the same when I fill and draw (if (first) h1_1->Fill(…) else h1_2->Fill(…)), and then there is no point in having one subroutine anymore. I might as well have two subroutines, doing exactly the same but with either h1_1 or h1_2. (Of course, this is fine, in this example, because I have only 1 histogram. But in real life, I actually have about 20 of them, so it really becomes ridiculous to have to copy the entire subroutine, just changing the histogram name).

If there would be something something like a “handle” for either h1_1 or h1_2, it would also help.
E.g.:
h1_handle = h1->GetHandle(); // would return either handle to h1_1 or to h1_2 h1_handle->Fill(...); h1_handle->Draw();
But I could not find any method like that.

Maybe there is some really obvious way to solve this, but for the moment I have settled for the Memory Leak warning, which is annoying but at least it works. (If I could delete the histograms without deleting them on the canvasses, that would be fine too).

Best regards,

Machiel

2

You could “compute” the names of your histograms: [code]#include “TROOT.h”
#include “TH2.h”

#include

void trial(void)
{
static Int_t HistoID = 1; // “static histo counter”

TString name(“h1_”);
name += HistoID++; // h1_1, h1_2, h1_3, …

// delete the “old” object with the “name”, if it exists
if (gROOT && gROOT->FindObjectAny(name.Data()))
delete gROOT->FindObjectAny(name.Data());

std::string title(“My Histo”);

// create a new histogram
TH2D *h = new TH2D(name.Data(), title.c_str(), 100, -2.0, 2.0, 100, -2.0, 2.0);

// …
// h->Fill(x, y);
// …

h->Draw();

return;
}[/code]
Afterwards, in another part of your code, you can always “find” your histograms using something like: TH2D *h; gROOT->GetObject("h1_1", h); // instead of "h1_1" put the "name" of any of your TH2D if (h) std::cout << "... found it ..." << endl; if (h) h->Draw();
Instead of creating many histograms, you could also try: [code]#include “TROOT.h”
#include “TH2.h”

#include

void trial(void)
{
std::string title(“My Histo”);

// create a new histogram (always with the same “name”)
TH2D *h = new TH2D(“h1”, title.c_str(), 100, -2.0, 2.0, 100, -2.0, 2.0);

// …
// h->Fill(x, y);
// …

h->DrawCopy(); // instead of "h->Draw();"
delete h;

return;
}[/code]

3

Wow, thanks!
Your first solution looks very inventive, I am sure that will come in handy sooner or later.
For the moment, I am settling for the DrawCopy solution, which does not only solve this particular problem but quite a few others I had in the past (re-fitting the same histogram etc…)

Cheers,

Machiel