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--- root:troubleshooting [2010/11/06 15:08] – decianm
+++ root:troubleshooting [2013/06/14 12:14] (current) – nchiap
@@ Line 1: / Line 1: @@
-====== Troubleshooting in ROOT ======
+====== Root-files ======
+Root-files can be the source of various problems.
+Usually they are caused by hidden changes in the internal state of ROOT.
+ROOT stores the active directory and uses this to create new objects and look for existing ones.
+The active directory is changed when a new file is opened.
+This can lead to unexpected behaviours and hard to trace bugs.
 ===== Empty Files =====
-When you write a ROOT-file in a method with:
-<code>
+When you get an an empty ROOT-file, check the right order of the files.
-file->Write()
+Don't do
-</code>
+<code C>
-and the file exists, but is empty, check the right order of the files: Do
-<code>
-TFile* inputFile = TFile::Open("myInputFile.root");
 TFile* outputFile = new TFile("myOutputFile.root", "RECREATE");
+TFile* inputFile = TFile::Open("myInputFile.root");
 // your code
 outputFile->Write();
 </code>
-but don't
-<code>
+but instead do:
-TFile* outputFile = new TFile("myOutputFile.root", "RECREATE");
+<code C>
 TFile* inputFile = TFile::Open("myInputFile.root");
+TFile* outputFile = new TFile("myOutputFile.root", "RECREATE");
 // your code
 outputFile->Write();
 </code>
-===== Change Marker Style =====
-To change the marker style, you have to do:
-<code C++>
-TGraph* myGraph = TGraph();
-...
-myGraph->Draw();
-myGraph->SetMarkerStyle(20);
-</code>
-but it will not work if the marker style is set before the graph is drawn.
-as your file will be empty.

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