If statements in for loops

ROOT
1

Some macros of mine are being plagued by this rather awkward problem of which I’ve just recently found the problem.

The following macro works fine

void test()
{
    
    if(0)
    {
        
        ntuple->get;     
    }
    else
    {
        cout << "Success" << endl;
    }
    
}

Run it and ROOT returns “Success”. Everything is good.

But if you imbed this same if statement in a loop,

void test()
{
    
    for(Int_t j = 0; j < 5; j++)
    {
        if(0)
        {
            
            ntuple->get;     
        }
        else
        {
            cout << "Success" << endl;
        }
    
    }
}

ROOT returns

Error: non class,struct,union object $ntuple used with . or -> FILE:test.c LINE:9
*** Interpreter error recovered ***

Why does a for loop cause ROOT to look into the statements that shouldn’t be executed?

I know “ntuple->get” doesn’t make any sense, but if you use a more appropriate construction the same problem occurs.

I’m using 4.04/02 on OS X, but the same problem occurs on a PC running an older version of ROOT.

Thanks for any help!

2

Hi,

CINT has a byte-code compilation step that requires the parsing of all the code paths.

Philippe

3

So if CINT parses all of the paths, is there anyway to do something like

if(file exists)
{
load file
load ntuple data
project ntuple data into histogram
fit histogram to “gaus”, for example
retrieve fit parameters
}

without receiving an error? If the file doesn’t exist and the statements are not executed, ROOT complains that “gaus” (or any other fit function) isn’t a struct, class, etc, when I try guas->GetParameter(0).

Thanks

4

Hi,

You may have to replace some CINT shorcuts by their C++ equivalent. For example:if (file_exist) { TFile *file = TFile::Open("myfile.root"); TTree *tree; file->GetObject("mytree",tree); if (tree==0) { cerr << "tree not found\n"; return; } tree->Draw("myval>>myhisto"); TH1F *h; gDirectory->GetObject("myhisto",h); h->Fit("gaus"); // and since gaus is a builtin TF1: TF1 *g = (TF1*)gROOT->GetListOfFunctions()->FindObject("gaus"); }Cheers,
Philippe

5

I see. Being new to ROOT (and C++ for that matter) I didn’t really notice the difference between CINT and C++ itself. Thanks!