Thread: Quick Question on ROOT and C++

Just a quick question. I was asked to do a set of things with ROOT to create a macro:

1) Create histogram using this command TH1F *h = new TH1F("h", "h", 60,0,60);
2) Open a root file
3) Then from flasher in this root file use Draw function to draw om number in this histogram under the condition that we have string number 62 and om number 2
4) Use command GetEntries() to get number of events


Now I created the histogram with that TH1F command, then I opened the ROOT file with TFile...after that though I don't know how to use the Draw function. I can seperately do mytree->Draw(...) but how do I get that plot into my *h histogram I created? That way when I input h.Draw() I will see the plot of my unique histogram that has the required conditions. Step 4 is simple but step 3 is confusing.

I can draw the histogram and have it printed out, but how do i have it saved into my TH1F historgram? is it just a simple command? like something that needs to be put into the parentheses?


Thanks in advance
Drew

Originally Posted by Salem

> It's not well known outside of scientists
So what makes you think we would know anything about it?

If you've got a question about C++ (like how does new call constructors), then write your question in standard C++ terms.

If you've got specific library issues, then the best place would be the documentation and support forums for the library you're using.


There are many 1000's of libraries in the world. The chance that you could pick a random programming forum and find experts in your chosen library is pretty well zero. Especially as you already admit is "not well known".

Well most of the commands in ROOT are written in C++, I have used this site for C++ training. So I wanted to come here to get help. Obviously that was a bad choice though, thanks for informing me.