How can I delete the objects?

Hi Rooters,
I’m writing a small macro like this
if()----->First if statement
TMultiGraph* stack = new TMultiGraph;

if()----->Second if statement
THStack* stack = new THStack;
When I run it, the code will crash, complaining “stack” already declared as different type.
I add two lines “delete stack; stack = NULL;” at the end of the first if statement, then program can work, but still giving out an error.
So My questions are:
Why is this case? I think that the two stacks are in different scopes.
How can I deal with the memory in ROOT? It seems the “delete stack; stack = NULL” has not deleted the object fully.
If I have defined several objects, like TH1*, TGraph*, TLegend*, do I really have to delete them? How can I do that? Sometimes deleting an object will cause a crash(not a NULL object).

Thank you very much.

I assume you’re using CINT here. I have found that the scoping rules are not the same as for standard C++ in CINT, so I’m not surprised by the problem you’re having.

Also, I think these days the accepted practice is to set pointers to 0 rather than NULL after a delete.

The code you have should work if you compile it. If you want to continue to use CINT for it, you should probably either come up with a different name for the second pointer or cast it to the correct pointer type before you allocate the memory the second time.

Now that I think more about it, I don’t think you could cast the pointer. However, if you’re using CINT you can simply let it allocate the pointers automatically. For example, using 2 different TH1 types:

bool select = true; if (select) { h = new TH1F("test", "test", 10, 0., 10.); } else { h = new TH1D("test", "test", 10, 0., 10.); } This will give you back h as either a TH1F or TH1D pointer. And yes, h will still be in scope after the if statement block.

Again, compiling is the best way to do things if you want to keep yourself within C++ scoping rules. Variable scoping in CINT is, to me at least, quite confusing.


thanks bdrell for helping us out! Yes, CINT fails to track variables’ scopes. The best solution is to use different variable names.

Cheers, Axel.