class TDirectoryFile: public TDirectory

Directory default constructor-
*-*                    =============================

 Create a new DirectoryFile *-*-
*-*                     ==========================
  A new directory with name,title is created in the current directory
  The directory header information is immediatly saved on the file
  A new key is added in the parent directory

  When this constructor is called from a class directly derived
  from TDirectoryFile, the third argument classname MUST be specified.
  In this case, classname must be the name of the derived class.

  Note that the directory name cannot contain slashes.

 Copy constructor.

 -- Destructor.

 Append object to this directory.

 If replace is true:
   remove any existing objects with the same same (if the name is not ""

-*-*-*Insert key in the linked list of keys of this directory
*-*          =======================================================

 Browse the content of the directory.

-*-*Initialise directory to defaults
*-*                    ================================

 Change current directory to "this" directory . Using path one can
 change the current directory to "path". The absolute path syntax is:
 file.root:/dir1/dir2
 where file.root is the file and /dir1/dir2 the desired subdirectory
 in the file. Relative syntax is relative to "this" directory. E.g:
 ../aa. Returns kTRUE in case of success.

 Clean the pointers to this object (gDirectory, TContext, etc.)

 Make a clone of an object using the Streamer facility.
 If the object derives from TNamed, this function is called
 by TNamed::Clone. TNamed::Clone uses the optional argument newname to set
 a new name to the newly created object.

 If autoadd is true and if the object class has a
 DirectoryAutoAdd function, it will be called at the end of the
 function with the parameter gDirector.  This usually means that
 the object will be appended to the current ROOT directory.

 Scan the memory lists of all files for an object with name

 Find a directory named "apath".
 It apath is null or empty, returns "this" directory.
 Otherwise use the name "apath" to find a directory.
 The absolute path syntax is:
    file.root:/dir1/dir2
 where file.root is the file and /dir1/dir2 the desired subdirectory
 in the file. Relative syntax is relative to "this" directory. E.g:
 ../aa.
 Returns 0 in case path does not exist.
 If printError is true, use Error with 'funcname' to issue an error message.

 -- Delete all objects from memory and directory structure itself.

Delete Objects or/and keys in a directory
*-*             =========================================
   namecycle has the format name;cycle
   namecycle = "" same as namecycle ="T*"
   name  = * means all
   cycle = * means all cycles (memory and keys)
   cycle = "" or cycle = 9999 ==> apply to a memory object
   When name=* use T* to delete subdirectories also

   To delete one directory, you must specify the directory cycle,
      eg.  file.Delete("dir1;1");

   examples:
     foo   : delete object named foo in memory
     foo*  : delete all objects with a name starting with foo
     foo;1 : delete cycle 1 of foo on file
     foo;* : delete all cycles of foo on file and also from memory
     *;2   : delete all objects on file having the cycle 2
     *;*   : delete all objects from memory and file
    T*;*   : delete all objects from memory and file and all subdirectories
          WARNING
    If the key to be deleted contains special characters ("+","^","?", etc
    that have a special meaning for the regular expression parser (see TRegexp)
    then you must specify 2 backslash characters to escape the regular expression.
    For example, if the key to be deleted is namecycle = "C++", you must call
       mydir.Delete("C\\+\\+")).

-*-*-*-*-*-*Encode directory header into output buffer
*-*                    =========================================

 Find key with name keyname in the current directory

 Find key with name keyname in the current directory or
 its subdirectories.
 NOTE that If a key is found, the directory containing the key becomes
 the current directory

 Find object by name in the list of memory objects of the current
 directory or its sub-directories.
 After this call the current directory is not changed.
 To automatically set the current directory where the object is found,
 use FindKeyAny(aname)->ReadObj().

  return pointer to object identified by namecycle

   namecycle has the format name;cycle
   name  = * is illegal, cycle = * is illegal
   cycle = "" or cycle = 9999 ==> apply to a memory object

   examples:
     foo   : get object named foo in memory
             if object is not in memory, try with highest cycle from file
     foo;1 : get cycle 1 of foo on file

  The retrieved object should in principle derive from TObject.
  If not, the function TDirectoryFile::GetObject should be called.
  However, this function will still work for a non-TObject, providing that
  the calling application cast the return type to the correct type (which
  is the actual type of the object).

  NOTE:
  The method GetObject offers better protection and avoids the need
  for any cast:
      MyClass *obj;
      directory->GetObject("some object",obj);
      if (obj) { ... the object exist and inherits from MyClass ... }

  VERY IMPORTANT NOTE:
  In case the class of this object derives from TObject but not
  as a first inheritance, one must use dynamic_cast<>().
  Example 1: Normal case:
      class MyClass : public TObject, public AnotherClass
   then on return, one can do:
      MyClass *obj = (MyClass*)directory->Get("some object of MyClass");

  Example 2: Special case:
      class MyClass : public AnotherClass, public TObject
  then on return, one must do:
      MyClass *obj = dynamic_cast<MyClass*>(directory->Get("some object of MyClass"));

  Of course, dynamic_cast<> can also be used in the example 1.

 return pointer to object identified by namecycle.
 The returned object may or may not derive from TObject.

   namecycle has the format name;cycle
   name  = * is illegal, cycle = * is illegal
   cycle = "" or cycle = 9999 ==> apply to a memory object

  VERY IMPORTANT NOTE:
  The calling application must cast the returned object to
  the final type, eg
      MyClass *obj = (MyClass*)directory->GetObject("some object of MyClass");

 See documentation of TDirectoryFile::GetObjectCheck(const char *namecycle, const TClass *cl)

 return pointer to object identified by namecycle if and only if the actual
 object is a type suitable to be stored as a pointer to a "expectedClass"
 If expectedClass is null, no check is performed.

   namecycle has the format name;cycle
   name  = * is illegal, cycle = * is illegal
   cycle = "" or cycle = 9999 ==> apply to a memory object

  VERY IMPORTANT NOTE:
  The calling application must cast the returned pointer to
  the type described by the 2 arguments (i.e. cl):
      MyClass *obj = (MyClass*)directory->GetObjectChecked("some object of MyClass","MyClass"));

  Note: We recommend using the method TDirectoryFile::GetObject:
      MyClass *obj = 0;
      directory->GetObject("some object inheriting from MyClass",obj);
      if (obj) { ... we found what we are looking for ... }

 Return the buffer size to create new TKeys.
 If the stored fBufferSize is null, the value returned is the average
 buffer size of objects in the file so far.

-*-*-*Return pointer to key with name,cycle
*-*                  =====================================
  if cycle = 9999 returns highest cycle

List Directory contents*-*-
*-*                    =======================
  Indentation is used to identify the directory tree
  Subdirectories are listed first, then objects in memory, then objects on the file

  The option can has the following format:
     [-d |-m][<regexp>]
  Option -d means: only list objects in the file
         -m means: only list objects in memory
  The <regexp> will be used to match the name of the objects.
  By default memory and disk objects are listed.

 Interface to TFile::Open

 Create a sub-directory and return a pointer to the created directory.
 Returns 0 in case of error.
 Returns 0 if a directory with the same name already exists.
 Note that the directory name may be of the form "a/b/c" to create a hierarchy of directories.
 In this case, the function returns the pointer to the "a" directory if the operation is successful.

 Purge lowest key cycles in a directory.
 By default, only the highest cycle of a key is kept. Keys for which
 the "KEEP" flag has been set are not removed. See TKey::Keep().

 Read objects from a ROOT db file directory into memory.
 If an object is already in memory, the memory copy is deleted
 and the object is again read from the file.
 If opt=="dirs", only subdirectories will be read
 If opt=="dirs*" complete directory tree will be read

Read the KEYS linked list
*-*                      =========================
  Every directory has a linked list (fKeys). This linked list has been
  written on the file via WriteKeys as a single data record.

  It is interesting to call this function in the following situation.
  Assume another process1 is connecting this directory in Update mode
    -Process1 is adding/updating objects in this directory
    -You want to see the latest status from process1.
  Example Process1:
    obj1.Write();
    obj2.Write();
    gDirectory->SaveSelf();

  Example Process2
    gDirectory->ReadKeys();
    obj1->Draw();

  This is an efficient way (without opening/closing files) to view
  the latest updates of a file being modified by another process
  as it is typically the case in a data acquisition system.

 Read object with keyname from the current directory
 Read contents of object with specified name from the current directory.
 First the key with keyname is searched in the current directory,
 next the key buffer is deserialized into the object.
 The object must have been created before via the default constructor.
 See TObject::Write().

 Removes subdirectory from the directory
 When diredctory is deleted, all keys in all subdirectories will be
 read first and deleted from file (if exists)
 Equivalent call is Delete("name;*");

*-*-*-*-*Save recursively all directory keys and headers
*-*                ===============================================

 Save object in filename,
 if filename is 0 or "", a file with "objectname.root" is created.
 The name of the key is the object name.
 If the operation is successful, it returns the number of bytes written to the file
 otherwise it returns 0.
 By default a message is printed. Use option "q" to not print the message.

Save Directory keys and header*-*-
*-*                ==============================
  If the directory has been modified (fModified set), write the keys
  and the directory header. This function assumes the cd is correctly set.

  It is recommended to use this function in the following situation:
  Assume a process1 using a directory in Update mode
    -New objects or modified objects have been written to the directory
    -You do not want to close the file
    -You want your changes be visible from another process2 already connected
     to this directory in read mode
    -Call this function
    -In process2, use TDirectoryFile::ReadKeys to refresh the directory

 set the default buffer size when creating new TKeys
 see also TDirectoryFile::GetBufferSize

 Find the action to be executed in the dictionary of the parent class
 and store the corresponding exec number into fBits.
 This function searches a data member in the class of parent with an
 offset corresponding to this.
 If a comment "TEXEC:" is found in the comment field of the data member,
 the function stores the exec identifier of the exec statement
 following this keyword.

  Set the new value of fWritable recursively

Return the size in bytes of the directory header
*-*          ================================================
Int_t nbytes = sizeof(Version_t);    2
nbytes     += fDatimeC.Sizeof();
nbytes     += fDatimeM.Sizeof();
nbytes     += sizeof fNbytesKeys;    4
nbytes     += sizeof fNbytesName;    4
nbytes     += sizeof fSeekDir;       4 or 8
nbytes     += sizeof fSeekParent;    4 or 8
nbytes     += sizeof fSeekKeys;      4 or 8
nbytes     += fUUID.Sizeof();

Stream a class object*-*-*-*-*-*-*-
*-*              =========================================

 Write all objects in memory to disk.
 Loop on all objects in memory (including subdirectories).
 A new key is created in the KEYS linked list for each object.
 For allowed options see TObject::Write().
 The directory header info is rewritten on the directory header record.

 One can not save a const TDirectory object.

 Write object obj to this directory
 The data structure corresponding to this object is serialized.
 The corresponding buffer is written to this directory
 with an associated key with name "name".

 Writing an object to a file involves the following steps:

  -Creation of a support TKey object in the directory.
   The TKey object creates a TBuffer object.

  -The TBuffer object is filled via the class::Streamer function.

  -If the file is compressed (default) a second buffer is created to
   hold the compressed buffer.

  -Reservation of the corresponding space in the file by looking
   in the TFree list of free blocks of the file.

  -The buffer is written to the file.

  By default, the buffersize will be taken from the average buffer size
  of all objects written to the current file so far.
  Use TDirectoryFile::SetBufferSize to force a given buffer size.

  If a name is specified, it will be the name of the key.
  If name is not given, the name of the key will be the name as returned
  by obj->GetName().

  The option can be a combination of:
    "SingleKey", "Overwrite" or "WriteDelete"
  Using the "Overwrite" option a previous key with the same name is
  overwritten. The previous key is deleted before writing the new object.
  Using the "WriteDelete" option a previous key with the same name is
  deleted only after the new object has been written. This option
  is safer than kOverwrite but it is slower.
  The "SingleKey" option is only used by TCollection::Write() to write
  a container with a single key instead of each object in the container
  with its own key.

  An object is read from this directory via TDirectoryFile::Get.

  The function returns the total number of bytes written to the directory.
  It returns 0 if the object cannot be written.

  WARNING: in name avoid special characters like '^','$','.' that are used
  by the regular expression parser (see TRegexp).

 Write object from pointer of class classname in this directory
 obj may not derive from TObject
 see TDirectoryFile::WriteTObject for comments

 VERY IMPORTANT NOTE:
    The value passed as 'obj' needs to be from a pointer to the type described by classname
    For example with:
      TopClass *top;
      BottomClass *bottom;
      top = bottom;
    you can do:
      directory->WriteObjectAny(top,"top","name of object");
      directory->WriteObjectAny(bottom,"bottom","name of object");
    BUT YOU CAN NOT DO (it will fail in particular with multiple inheritance):
      directory->WriteObjectAny(top,"bottom","name of object");

 We STRONGLY recommend to use
      TopClass *top = ....;
      directory->WriteObject(top,"name of object")

   see laso remarks in TDirectoryFile::WriteTObject

 Write object of class with dictionary cl in this directory
 obj may not derive from TObject
 To get the TClass* cl pointer, one can use
    TClass *cl = TClass::GetClass("classname");
 An alternative is to call the function WriteObjectAny above.
 see TDirectoryFile::WriteTObject for comments

-*-*Overwrite the Directory header record
*-*                  =====================================

-*-*-*-*Write KEYS linked list on the file 
*-*                    ==================================
  The linked list of keys (fKeys) is written as a single data record