TFile

 File default Constructor.

 Opens or creates a local ROOT file whose name is fname1. It is
 recommended to specify fname1 as "<file>.root". The suffix ".root"
 will be used by object browsers to automatically identify the file as
 a ROOT file. If the constructor fails in any way IsZombie() will
 return true. Use IsOpen() to check if the file is (still) open.

 To open non-local files use the static TFile::Open() method, that
 will take care of opening the files using the correct remote file
 access plugin.

 If option = NEW or CREATE   create a new file and open it for writing,
                             if the file already exists the file is
                             not opened.
           = RECREATE        create a new file, if the file already
                             exists it will be overwritten.
           = UPDATE          open an existing file for writing.
                             if no file exists, it is created.
           = READ            open an existing file for reading.
           = NET             used by derived remote file access
                             classes, not a user callable option
           = WEB             used by derived remote http access
                             class, not a user callable option

 The file can be specified as a URL of the form:
    file:///user/rdm/bla.root or file:/user/rdm/bla.root

 The file can also be a member of an archive, in which case it is
 specified as:
    multi.zip#file.root or multi.zip#0
 which will open file.root which is a member of the file multi.zip
 archive or member 1 from the archive. For more on archive file
 support see the TArchiveFile class.

 TFile and its remote access plugins can also be used to open any
 file, i.e. also non ROOT files, using:
    file.tar?filetype=raw
 This is convenient because the many remote file access plugins allow
 easy access to/from the many different mass storage systems.

 The title of the file (ftitle) will be shown by the ROOT browsers.

 A ROOT file (like a Unix file system) may contain objects and
 directories. There are no restrictions for the number of levels
 of directories.

 A ROOT file is designed such that one can write in the file in pure
 sequential mode (case of BATCH jobs). In this case, the file may be
 read sequentially again without using the file index written
 at the end of the file. In case of a job crash, all the information
 on the file is therefore protected.

 A ROOT file can be used interactively. In this case, one has the
 possibility to delete existing objects and add new ones.
 When an object is deleted from the file, the freed space is added
 into the FREE linked list (fFree). The FREE list consists of a chain
 of consecutive free segments on the file. At the same time, the first
 4 bytes of the freed record on the file are overwritten by GAPSIZE
 where GAPSIZE = -(Number of bytes occupied by the record).

 Option compress is used to specify the compression level:
  compress = 0 objects written to this file will not be compressed.
  compress = 1 minimal compression level but fast.
  ....
  compress = 9 maximal compression level but slow.

 Note that the compression level may be changed at any time.
 The new compression level will only apply to newly written objects.
 The function TFile::Map() shows the compression factor
 for each object written to this file.
 The function TFile::GetCompressionFactor returns the global
 compression factor for this file.

 In case the file does not exist or is not a valid ROOT file,
 it is made a Zombie. One can detect this situation with a code like:
    TFile f("file.root");
    if (f.IsZombie()) {
       cout << "Error opening file" << endl;
       exit(-1);
    }

 A ROOT file is a suite of consecutive data records (TKey's) with
 the following format (see also the TKey class). If the key is
 located past the 32 bit file limit (> 2 GB) then some fields will
 be 8 instead of 4 bytes:
    1->4            Nbytes    = Length of compressed object (in bytes)
    5->6            Version   = TKey version identifier
    7->10           ObjLen    = Length of uncompressed object
    11->14          Datime    = Date and time when object was written to file
    15->16          KeyLen    = Length of the key structure (in bytes)
    17->18          Cycle     = Cycle of key
    19->22 [19->26] SeekKey   = Pointer to record itself (consistency check)
    23->26 [27->34] SeekPdir  = Pointer to directory header
    27->27 [35->35] lname     = Number of bytes in the class name
    28->.. [36->..] ClassName = Object Class Name
    ..->..          lname     = Number of bytes in the object name
    ..->..          Name      = lName bytes with the name of the object
    ..->..          lTitle    = Number of bytes in the object title
    ..->..          Title     = Title of the object
    ----->          DATA      = Data bytes associated to the object

 The first data record starts at byte fBEGIN (currently set to kBEGIN).
 Bytes 1->kBEGIN contain the file description, when fVersion >= 1000000
 it is a large file (> 2 GB) and the offsets will be 8 bytes long and
 fUnits will be set to 8:
    1->4            "root"      = Root file identifier
    5->8            fVersion    = File format version
    9->12           fBEGIN      = Pointer to first data record
    13->16 [13->20] fEND        = Pointer to first free word at the EOF
    17->20 [21->28] fSeekFree   = Pointer to FREE data record
    21->24 [29->32] fNbytesFree = Number of bytes in FREE data record
    25->28 [33->36] nfree       = Number of free data records
    29->32 [37->40] fNbytesName = Number of bytes in TNamed at creation time
    33->33 [41->41] fUnits      = Number of bytes for file pointers
    34->37 [42->45] fCompress   = Zip compression level
    38->41 [46->53] fSeekInfo   = Pointer to TStreamerInfo record
    42->45 [54->57] fNbytesInfo = Number of bytes in TStreamerInfo record
    46->63 [58->75] fUUID       = Universal Unique ID

 The structure of a directory is shown in TDirectory::TDirectory

 Copy constructor.

 File destructor.

 Initialize a TFile object.
 TFile implementations providing asynchronous open functionality need to
 override this method to run the appropriate checks before calling this
 standard initialization part. See TXNetFile::Init for an example.

 Close a file.
 If option == "R", all TProcessIDs referenced by this file are deleted.
 Calling TFile::Close("R") might be necessary in case one reads a long list
 of files having TRef, writing some of the referenced objects or TRef
 to a new file. If the TRef or referenced objects of the file being closed
 will not be referenced again, it is possible to minimize the size
 of the TProcessID data structures in memory by forcing a delete of
 the unused TProcessID.

 Creates key for object and converts data to buffer.

 Creates key for object and converts data to buffer.

 Delete object namecycle.
 Namecycle identifies an object in the top directory of the file
   namecycle has the format name;cycle
   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

 Examples:
     foo   : delete object named foo in memory
     foo;1 : delete cycle 1 of foo on file
     foo;* : delete all cycles of foo on disk 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

 Fill Graphics Structure and Paint.
 Loop on all objects (memory or file) and all subdirectories.

 Draw map of objects in this file.

 Synchronize a file's in-core and on-disk states.

 Flush the write cache if active.
 Return kTRUE in case of error

 Encode file output buffer.
 The file output buffer contains only the FREE data record.

 Return the best buffer size of objects on this file.
 The best buffer size is estimated based on the current mean value
 and standard deviation of all objects written so far to this file.
 Returns mean value + one standard deviation.

 Return the file compression factor.
 Add total number of compressed/uncompressed bytes for each key.
 return ratio of the two.

 Method returning errno. Is overriden in TRFIOFile.

 Method resetting the errno. Is overridden in TRFIOFile.

 Return a pointer to the current read cache.

 Return a pointer to the current write cache.

 Read the logical record header starting at position first.
 Maxbytes bytes are read into buf the function reads nread bytes
 where nread is the minimum of maxbytes and the number of bytes
 before the end of file. The function returns nread.
 In output arguments:
    nbytes : number of bytes in record
             if negative, this is a deleted record
             if 0, cannot read record, wrong value of argument first
    objlen : uncompressed object size
    keylen : length of logical record header
 Note that the arguments objlen and keylen are returned only
 if maxbytes >=16

 Returns the current file size. Returns -1 in case the file could not
 be stat'ed.

 Returns the cached list of StreamerInfos used in this file.

 Read the list of TStreamerInfo objects written to this file.
 The function returns a TList. It is the user'responsability
 to delete the list created by this function.

 Using the list, one can access additional information,eg:
   TFile f("myfile.root");
   TList *list = f.GetStreamerInfoList();
   TStreamerInfo *info = (TStreamerInfo*)list->FindObject("MyClass");
   Int_t classversionid = info->GetClassVersion();
   delete list;

 List File contents.
 Indentation is used to identify the file tree.
 Subdirectories are listed first, then objects in memory,
 then objects on the file.

 Returns kTRUE in case file is open and kFALSE if file is not open.

 Mark unused bytes on the file.
 The list of free segments is in the fFree linked list.
 When an object is deleted from the file, the freed space is added
 into the FREE linked list (fFree). The FREE list consists of a chain
 of consecutive free segments on the file. At the same time, the first
 4 bytes of the freed record on the file are overwritten by GAPSIZE
 where GAPSIZE = -(Number of bytes occupied by the record).

 List the contents of a file sequentially.
 For each logical record found, it prints:
  Date/Time  Record_Adress Logical_Record_Length  ClassName  CompressionFactor

  Example of output
  20010404/150437  At:64        N=150       TFile
  20010404/150440  At:214       N=28326     TBasket        CX =  1.13
  20010404/150440  At:28540     N=29616     TBasket        CX =  1.08
  20010404/150440  At:58156     N=29640     TBasket        CX =  1.08
  20010404/150440  At:87796     N=29076     TBasket        CX =  1.10
  20010404/150440  At:116872    N=10151     TBasket        CX =  3.15
  20010404/150441  At:127023    N=28341     TBasket        CX =  1.13
  20010404/150441  At:155364    N=29594     TBasket        CX =  1.08
  20010404/150441  At:184958    N=29616     TBasket        CX =  1.08
  20010404/150441  At:214574    N=29075     TBasket        CX =  1.10
  20010404/150441  At:243649    N=9583      TBasket        CX =  3.34
  20010404/150442  At:253232    N=28324     TBasket        CX =  1.13
  20010404/150442  At:281556    N=29641     TBasket        CX =  1.08
  20010404/150442  At:311197    N=29633     TBasket        CX =  1.08
  20010404/150442  At:340830    N=29091     TBasket        CX =  1.10
  20010404/150442  At:369921    N=10341     TBasket        CX =  3.09
  20010404/150442  At:380262    N=509       TH1F           CX =  1.93
  20010404/150442  At:380771    N=1769      TH2F           CX =  4.32
  20010404/150442  At:382540    N=1849      TProfile       CX =  1.65
  20010404/150442  At:384389    N=18434     TNtuple        CX =  4.51
  20010404/150442  At:402823    N=307       KeysList
  20010404/150443  At:403130    N=4548      StreamerInfo   CX =  3.65
  20010404/150443  At:407678    N=86        FreeSegments
  20010404/150443  At:407764    N=1         END

 Paint all objects in the file.

 Print all objects in the file.

 Read a buffer from the file. This is the basic low level read operation.
 Returns kTRUE in case of failure.

 Read the nbuf blocks described in arrays pos and len,
 where pos[i] is the seek position of block i of length len[i].
 Note that for nbuf=1, this call is equivalent to TFile::ReafBuffer.
 This function is overloaded by TNetFile, TWebFile, etc.
 Returns kTRUE in case of failure.

 Read buffer via cache. Returns 0 if the requested block is
 not in the cache, 1 in case read via cache was successful,
 2 in case read via cache failed.

 Read the FREE linked list.
 Every file has a linked list (fFree) of free segments.
 This linked list has been written on the file via WriteFree
 as a single data record.

 Attempt to recover file if not correctly closed.
 The function returns the number of keys that have been recovered.
 If no keys can be recovered, the file will be declared Zombie by
 the calling function. This function is automatically called when
 opening a file.

 If the file is open in read only mode, the file is not modified.
 If open in update mode and the function finds something to recover,
  a new directory header is written to the file. When opening the file gain
  no message from Recover will be reported.
 If keys have been recovered, the file is usable and you can safely
 read the corresponding objects.
 If the file is not usable (a zombie), you can test for this case
 with code like:
   TFile f("myfile.root");
   if (f.IsZombie()) {file is unusable)
 If the file has been recovered, the bit kRecovered is set in the TFile object in memory.
 You can test if the file has been recovered with
   if (f.TestBit(TFile::kRecovered)) {.. the file has been recovered}

 When writing TTrees to a file, it is important to save the Tree header
 at regular intervals (see TTree::AutoSave). If a file containing a Tree
 is recovered, the last Tree header written to the file will be used.
 In this case all the entries in all the branches written before writing
 the header are valid entries.

 Reopen a file with a different access mode, like from READ to
 UPDATE or from NEW, CREATE, RECREATE, UPDATE to READ. Thus the
 mode argument can be either "READ" or "UPDATE". The method returns
 0 in case the mode was successfully modified, 1 in case the mode
 did not change (was already as requested or wrong input arguments)
 and -1 in case of failure, in which case the file cannot be used
 anymore. The current directory (gFile) is changed to this file.

 Seek to a specific position in the file. Pos it either kBeg, kCur or kEnd.

 Set level of compression for this file:
  level = 0 objects written to this file will not be compressed.
  level = 1 minimal compression level but fast.
  ....
  level = 9 maximal compression level but slow.

 Note that the compression level may be changed at any time.
 The new compression level will only apply to newly written objects.
 The function TFile::Map shows the compression factor
 for each object written to this file.
 The function TFile::GetCompressionFactor returns the global
 compression factor for this file.

 Set a pointer to the read cache.

 Set a pointer to the write cache.
 If file is null the existing write cache is deleted.

 Return the size in bytes of the file header.

 Stream a TFile object.

 Increment statistics for buffer sizes of objects in this file.

 Dummy function kept for backward compatibility.
 The read  cache is now managed by TFileCacheRead
 The write cache is now managed by TFileCacheWrite
 Both caches are created automatically by the system.

 Write memory objects to this file.
 Loop on all objects in memory (including subdirectories).
 A new key is created in the KEYS linked list for each object.
 The list of keys is then saved on the file (via WriteKeys)
 as a single data record.
 For values of opt see TObject::Write().
 The directory header info is rewritten on the directory header record.
 The linked list of FREE segments is written.
 The file header is written (bytes 1->fBEGIN).

 One can not save a const TDirectory object.

 Write a buffer to the file. This is the basic low level write operation.
 Returns kTRUE in case of failure.

 Write buffer via cache. Returns 0 if cache is not active, 1 in case
 write via cache was successful, 2 in case write via cache failed.

 Write FREE linked list on the file.
 The linked list of FREE segments (fFree) is written as a single data
 record.

 Write File Header.

 Generate code in directory dirname for all classes specified in argument classes
 If classes = "*" (default), the function generates an include file for each
 class in the StreamerInfo list for which a TClass object does not exist.
 One can restrict the list of classes to be generated by using expressions like:
   classes = "Ali*" generate code only for classes starting with Ali
   classes = "myClass" generate code for class MyClass only.

 If option = "new" (default) a new directory dirname is created.
                   If dirname already exist, an error message is printed
                   and the function returns.
 If option = "recreate", then;
                   if dirname does not exist, it is created (like in "new")
                   if dirname already exist, all existing files in dirname
                   are deleted before creating the new files.
 If option = "update", then new classes are added to the existing directory.
                   Existing classes with the same name are replaced by the
                   new definition. If the directory dirname doest not exist,
                   same effect as "new".
 If, in addition to one of the 3 above options, the option "+" is specified,
 the function will generate:
   - a script called MAKE to build the shared lib
   - a LinkDef.h file
   - rootcint will be run to generate a dirnameProjectDict.cxx file
   - dirnameProjectDict.cxx will be compiled with the current options in compiledata.h
   - a shared lib dirname.so will be created.
 If the option "++" is specified, the generated shared lib is dynamically
 linked with the current executable module.
 Example:
  file.MakeProject("demo","*","recreate++");
  - creates a new directory demo unless it already exist
  - clear the previous directory content
  - generate the xxx.h files for all classes xxx found in this file
    and not yet known to the CINT dictionary.
  - creates the build script MAKE
  - creates a LinkDef.h file
  - runs rootcint generating demoProjectDict.cxx
  - compiles demoProjectDict.cxx into demoProjectDict.o
  - generates a shared lib demo.so
  - dynamically links the shared lib demo.so to the executable
  If only the option "+" had been specified, one can still link the
  shared lib to the current executable module with:
     gSystem->load("demo/demo.so");

 Read the list of StreamerInfo from this file.
 The key with name holding the list of TStreamerInfo objects is read.
 The corresponding TClass objects are updated.
 Note that this function is not called if the static member fgReadInfo is falsse.
  (see TFile::SetReadStreamerInfo)

 static function to set fgReadInfo.
 If fgReadInfo is true (default) TFile::ReadStreamerInfo is called
  when opening the file.
 It may be interesting to set fgReadInfo to false to speedup the file
 opening time or in case libraries containing classes referenced
 by the file have not yet been loaded.
 if fgReadInfo is false, one can still read the StreamerInfo with
    myfile.ReadStreamerInfo();

 Show the StreamerInfo of all classes written to this file.

 Write the list of TStreamerInfo as a single object in this file
 The class Streamer description for all classes written to this file
 is saved. See class TStreamerInfo.

 Static member function allowing the creation/opening of either a
 TFile, TNetFile, TWebFile or any TFile derived class for which an
 plugin library handler has been registered with the plugin manager
 (for the plugin manager see the TPluginManager class). The returned
 type of TFile depends on the file name. If the file starts with
 "root:", "roots:" or "rootk:" a TNetFile object will be returned,
 with "http:" a TWebFile, with "file:" a local TFile, etc. (see the
 list of TFile plugin handlers in $ROOTSYS/etc/system.rootrc for regular
 expressions that will be checked) and as last a local file will be tried.
 Before opening a file via TNetFile a check is made to see if the URL
 specifies a local file. If that is the case the file will be opened
 via a normal TFile. To force the opening of a local file via a
 TNetFile use either TNetFile directly or specify as host "localhost".
 The netopt argument is only used by TNetFile. For the meaning of the
 options and other arguments see the constructors of the individual
 file classes. In case of error returns 0.

 Static member function to submit an open request. The request will be
 processed asynchronously. See TFile::Open(const char *, ...) for an
 explanation of the arguments. A handler is returned which is to be passed
 to TFile::Open(TFileOpenHandle *) to get the real TFile instance once
 the file is open.
 This call never blocks and it is provided to allow parallel submission
 of file opening operations expected to take a long time.
 TFile::Open(TFileOpenHandle *) may block if the file is not yet ready.
 The sequence
    TFile::Open(TFile::AsyncOpen(const char *, ...))
 is equivalent to
    TFile::Open(const char *, ...) .
 To be effective, the underlying TFile implementation must be able to
 support asynchronous open functionality. Currently, only TXNetFile
 supports it. If the functionality is not implemented, this call acts
 transparently by returning an handle with the arguments for the
 standard synchronous open run by TFile::Open(TFileOpenHandle *).
 The retuned handle will be adopted by TFile after opening completion
 in TFile::Open(TFileOpenHandle *); if opening is not finalized the
 handle must be deleted by the caller.

 Waits for the completion of an asynchronous open request.
 Returns the associated TFile, transferring ownership of the
 handle to the TFile instance.

 Interface to system open. All arguments like in POSIX open().

 Interface to system close. All arguments like in POSIX close().

 Interface to system read. All arguments like in POSIX read().

 Interface to system write. All arguments like in POSIX write().

 Interface to system lseek. All arguments like in POSIX lseek()
 except that the offset and return value are of a type which are
 able to handle 64 bit file systems.

 Return file stat information. The interface and return value is
 identical to TSystem::GetPathInfo(). The function returns 0 in
 case of success and 1 if the file could not be stat'ed.

 Interface to system fsync. All arguments like in POSIX fsync().

 Return the total number of bytes written so far to the file.

 Static function returning the total number of bytes read from all files.

 Static function returning the total number of bytes written to all files.
 Does not take into account what might still be in the write caches.

 Static function returning the total number of read calls from all files.

 Return kTRUE if 'url' matches the coordinates of this file.
 The check is implementation dependent and may need to be overload
 by each TFile implememtation relying on this check.
 The default implementation checks teh file name only.

 Get final URL for file being opened asynchronously.
 Returns 0 is the information is not yet available.

 Interface for text-based TDirectory I/O