This is C++ code.

Everything following a double slash '//' is a comment. Comments are meant 
for individuals reading through code, and are completely ignored by the 
compiler.

//--------------------------------------------------------------------------
// File and Version Information:
//	NTrkExample.hh	June 2005 
//
// Description:
//	Class NTrkExample 
//	This is an analysis module class used as the
//      first example in the offline workbook. 
//      The workbook can be found on the web at the
//	following URL:
//	BFROOT/www/doc/workbook/workbook.html
//
//      The NTrkExample class only plots a histogram of
//	the number of tracks per event.
//
// Environment:
//	Software developed for the BaBar Detector at the SLAC B-Factory
//
// Author List:
//      Charles Young                   Original Author
//      Tracey Marsh                    minimize module
//      Sheila Mclachlin                update 2005
//
//
// Copyright Information:
//	Copyright (C) 1997		
//
//------------------------------------------------------------------------

#ifndef NTRKEXAMPLE_HH
#define NTRKEXAMPLE_HH

These two lines are part of the preprocessor 
syntax to ensure that header files do not get included multiple times.

//----------------------
// Base Class Headers --
//----------------------
#include "Framework/AppModule.hh"
#include "AbsParm/AbsParmIfdStrKey.hh"
#include "AbsEvent/AbsEvent.hh"

The classes and member functions defined in the 
included header files can be used anywhere in this header file and 
in the implementation file NTrkExample.cc. If there are commands or 
classes that you do not recognize when looking through code, the 
included header files are a reasonable first place to look. These are 
all BaBar specific header files so they are enclosed by double 
quotes.

//------------------------------------
// Collaborating Class Declarations --
//------------------------------------

At compile time all of the types used in the 
declaration of the NTrkExample class must be known to the compiler. 
Since the NTrkExample class only has pointers to these class types, 
only the declaration and not the definition is needed at this time. 
The implementation file NTrkExample.cc will #include the header 
files that define these classes.

class HepHistogram;

//---------------------
//-- Class Interface --
//---------------------
 
class NTrkExample : public AppModule {

The NTrkExample class inherits from the AppModule class. 
This means that it has a common interface and must supply implementation for 
any virtual functions declared in the AppModule class. The structure of the 
NTrkExample class will be defined within the open and closed curly brackets 
'{' and '}'.

//--------------------
// Instance Members --
//--------------------

public:

Public members can be freely used by all code. For 
general purposes constructors and destructors should be made public. The 
member functions and data members that this class should "export" or make 
available for use by other applications should also be made public.

  // Constructors
  NTrkExample( const char* const theName, const char* const theDescription );

  // Destructor
  virtual ~NTrkExample( );

  // Operations

  virtual AppResult  beginJob( AbsEvent* anEvent );
  virtual AppResult  event( AbsEvent* anEvent );
  virtual AppResult  endJob  ( AbsEvent* anEvent );

protected:
  
Protected members can only be used or altered by 
classes that have been designated as friends of this class and by 
friends of classes derived from this one. In this case there are no 
protected members.

private:

Private members can only be used or altered by 
friends of this class. A class is a friend of itself. Typically, 
protected members contain the details of the class implementation.


  AbsParmIfdStrKey       _btaChargedList;

The first data member declared is named _btaChargedList 
and is of type AbsParmIfdStrKey. This type (class) is defined in the 
AbsParmIfdStrKey.hh file. 

  HepHistogram* _numTrkHisto;

The NTrkExample class declaration contains a pointer that is only 
allowed to point to an object of type HepHistogram and is named _numTrkHisto. 
Just the pointer is the data member of the class. The memory for the 
object that is pointed to does not belong to the class.

};

The NTrkExample class declaration is completed, the 
closed curly brace '}' ends the body and the semicolon ';' marks the end 
of the declaration.

#endif

This is the final line of the preprocessor if 
statement used to prevent multiple inclusion of header files.

The definition and implementation of this class's member functions are 
found in the NTrkExample.cc file.

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Last modification: Jan 2006
Last significant update: ?1999