Hello,
I am writing a C++ program that is using the ROOT libraries, which works fine. From the compiled C++ code, I would like to open a plot window (TCanvas) in the same way as it is done from the interpreter. What libraries should I link, and which code should I invoke for that?
Thank you
Dominique Eckert
Hi Dominique,
Depends on which platform, but if not on Windows, this command:`root-config --cflags --glibs`
Will give you the right compilation flags and set of libraries.
You can also take a look at $ROOTSYS/test/Makefile for example
And for the canvas, the same commands can be used in a compiled program than in the command line… I would say something like this:
Then it could also be declared as member of one of you classes. But this is not specific to ROOT, just create your TCanvas like any other C++ object (class). Just take a look at examples in $ROOTSYS/tutorials and $ROOTSYS/test
Cheers, Bertrand.
Hello Bertrand,
Thanks for the answer.
Actually, I was able to solve part of the problem myself: I found out about the “TApplication” class, which allows me to open a TCanvas. However, once this is done, I get stuck with the open TCanvas window and cannot continue running the software. For example:
[code]int main(int argc, char **argv){
TApplication theApp(“tapp”, &argc, argv);
TH1F *h = new TH1F(“h”,“h”,100,-3,3);
h->FillRandom(“gaus”,1000);
TCanvas *c1=new TCanvas(“c1”);
h->Draw();
c1->Update();
theApp.Run();
return 0;
}[/code]
While running this, everything gets stuck just after the “theApp.Run();” command, and I am never able to finish the program. What should I do for that?
Thanks
Dominique[/code]
Hi Dominique,
As reported several times at this forum, you should simply use the standard root.exe and invoke your script (interpreted or compiled via ACLIC)
root > .x myscript.C (run via the CINT interpreter)
root > .x myscript.C+ (run using native code compiled by ACLIC)
The standard root.exe includes the event loop manager TRInt derived from TApplication. You can leave with the normal command “.q” or by selecting “Quit ROOT” from the canvas “File” menu.
In your case where you use simply a TApplication, you can leave the application via the canvas “File” menu.
Rene
Dear Rene,
Thanks, but I know that already. In this case, I am developping a standalone application that I am compiling outside of the ROOT interpreter for other purposes. I would like to use the ROOT plotting tools inside.
What should I do in this case?
Thanks
Dominique
It does not matter if you develop a “standalone” application or not. It also depends what you mean by “plotting tools”. If you simply need to produce histograms or pdf, ps files in batch, you do not need classes like TApplication, TRint.
BUT, if you want to interact with your canvases, you need a TApplication (or better TRint).
So far, I have not seen any single case where writing a main program was justified :
Rene
OK, let me explain the details a bit more.
I am an astronomer, and in astronomy the data are generally stored in so-called FITS files. There exists an API called CFITSIO that makes it possible to access FITS files from C++ programs (but not from ROOT).
My goal here is to provide to the people of my institute a software that would do interactively some tasks specific to astronomy. To do that, I have to access FITS files, and therefore I need to use CFITSIO. But since I am familiar with ROOT for computational tasks and to display the results (so, yes, I need to interact with the canvases). For this reason, I need to make a standalone application. I hope you understand the reason a bit better.
Could you please explain me (or point me to the appropriate documentation) how the TApplication and/or TRint classes should be used?
Thanks
Dominique
Dominique,
Why don’t you write a myscript.C file where you invoke the CFITSIO system?
Simply add the relevant includes in myscript.C and do something like
root > gSystem->Load("libCFITSIO"); //or whatever it is
root > .x myscript.C+
Rene
Thanks Rene, I will try that.
Dominique
We have plenty of CFITSIO ROOT-based applications.
(most of them from BNL lsst.org/lsst LSST group).
It is used the way Rene has described
Let me know if you have any CFITSIO ROOT specific questions.
Since I am also interested in this kind of things:
So does it mean that I can’t create a standalone project which includes ROOT libraries, if I want interactivity?
But I can create an application which includes ROOT libraries and the interactivity is not due to ROOT objects.
So I should be fine if I do fitting, histogram creation and writing a ROOT file
without using CINT, right?
You can create your own application using the ROOT libraries, eg creating, filling histograms, trees, saving them in a ROOT file.
You need to include a TApplication (or TRint) object if you want to interact with the canvas,
have menus, edit graphics objects.
Rene
[quote=“Luke_K”]Since I am also interested in this kind of things:
So does it mean that I can’t create a standalone project which includes ROOT libraries, if I want interactivity?
But I can create an application which includes ROOT libraries and the interactivity is not due to ROOT objects.
So I should be fine if I do fitting, histogram creation and writing a ROOT file
without using CINT, right?[/quote]It doesn’t matter how you create the main subroutine. Either way, ROOT libraries use the CINT facilities internally. This means creating your own so-called stand-alone application you are asking for the extra troubles and gain nothing.
You always can start ROOT in the batch mode from the shell script. This way no interactive session (ROOT / Cint command prompt) is created (is it your concern?)root.exe -b -q -l 'MyScript.C++("my parameters")' This is how we use it to process our data.
Your script can use any interactive tools. There is no constrain.
-b option stands for the “batch”. The “batch” term means ROOT doesn’t not use the real screen to render its object.
The option “-q” means that the ROOT session is to be terminated automatically as soon as your script ends.
If you need ROOT graphics omit -b and use
Batch is what I’m using so far (gROOT.SetBatch()).
Ok, I understand.
So it was my misconception of PyROOT.
Since I can write PyROOT applications without using CINT explicitly (i.e. by ‘python myprogram’) I thought the same should be possible with C++:
$ g++ myROOTApp.cc -o myApp -l ROOTlibraries
$ ./myApp
or similar.
So the best option I came across so far is to build the Application with
#myApp.py
gROOT.SetBatch(True)
gSystem.CompileMacro("MyROOTApp.cc","k");
from ROOT import MyApp
app = MyApp()
app.SetParameter1()
...
app.run()
This I can start without calling the CINT explicitly and it behaves like a stand alone application.
Just for info, Pyroot uses extensively the information in the CINT data structures.
So, even if you do not use CINT at the command line, you still use behind the scene.
Rene
[quote=“Luke_K”]. . .
Since I can write PyROOT applications without using CINT explicitly (i.e. by ‘python myprogram’) I thought the same should be possible with C++:
. . …
So the best option I came across so far is to build the Application with#myApp.py
gROOT.SetBatch(True)
gSystem.CompileMacro("MyROOTApp.cc","k");
from ROOT import MyApp
app = MyApp()
app.SetParameter1()
...
app.run()This I can start without calling the CINT explicitly and it behaves like a stand alone application.[/quote]
Well, the best 
solution to make your application to behave like stand-alone application is to use the shell script 
myApp.
It requires ONE (at most) shell command instead of your 5 (at least) ‘python’ statements (+ redundant Python and PyROOT env + the Python language knowledge + knowledge of the Python /C++ binding + etc +etc ).
With your favorite text editor create the “myApp” text file:
#!/bin/sh
root.exe -b -q -l 'MyROOTApp.cxx+("'$1'")' Make it “executable”:chmod +x myAppAssuming ‘MyROOTApp.cc’:
#include <iostream>
void MyROOTApp(const char *helloWord) {std::cout << helloWord << endl; }The “application” myApp Hello_Luke_K produces:
./myApp Hello_Luke_K
Hello_Luke_KYou can go further by eliminating one file
Try to copy/paste/run the shell script below:
[code]#!/bin/sh
cat >MyROOTApp.cxx <<CPLUSCODE
#include
void MyROOTApp(const char *helloWord) {std::cout << helloWord << endl; }
CPLUSCODE
root.exe -b -q -l ‘MyROOTApp.cxx+("’$1’")’[/code]
[quote=“Luke_K”]. . . So it was my misconception of PyROOT. [/quote]In case of PyRoot the goal is to use ANOTHER language by some reason.
Well, it depends which way do you prefer, but I see no difference to my python method, which for me is easier to handle.
My misconception was that I thought PyROOT uses the ROOT libraries without using CINT. But I was told, that the libraries call CINT.
What is bothering me so far is that it is difficult to use an IDE (i.e. eclipse)
for debugging or to launch my application.
With PyROOT I found an easy way to launch the program with eclipse without
making changes to use root to execute (which I find not so easy to do).
For the debug issue I will start another thread, I feel like I hijacked this one 
:
root.cern.ch/phpBB2/viewtopic.php?p=42493#42493
[quote=“Luke_K”]…
I see no difference to my python method, which for me is easier to handle. . . . [/quote]I prefer the cheapest way. I do see the difference:
ROOT ::= C++ + CINTor
ROOT-CINT = C++I.e . ROOT without CINT is called C++.