class description - source file - inheritance tree

class TKey : public TNamed

virtual void Create(Int_t nbytes) virtual Int_t Read(const char* name) public:
TKey TKey() TKey TKey(const char* name, const char* title, TClass* cl, Int_t nbytes) TKey TKey(const TString& name, const TString& title, TClass* cl, Int_t nbytes) TKey TKey(TObject* obj, const char* name, Int_t bufsize) TKey TKey(Seek_t pointer, Int_t nbytes) TKey TKey(const TKey&) virtual void ~TKey() virtual void Browse(TBrowser* b) static TClass* Class() virtual void Delete(Option_t* option) virtual void DeleteBuffer() virtual void FillBuffer(char*& buffer) virtual char* GetBuffer() const TBuffer* GetBufferRef() const virtual const char* GetClassName() const Short_t GetCycle() const Short_t GetKeep() const Int_t GetKeylen() const Int_t GetNbytes() const Int_t GetObjlen() const virtual Seek_t GetSeekKey() const virtual Seek_t GetSeekPdir() const Int_t GetVersion() const virtual ULong_t Hash() const virtual TClass* IsA() const virtual Bool_t IsFolder() const virtual void Keep() virtual void ls(Option_t* option) const virtual void Print(Option_t* option) const virtual Int_t Read(TObject* obj) virtual void ReadBuffer(char*& buffer) virtual void ReadFile() virtual TObject* ReadObj() virtual void SetBuffer() virtual void SetParent(TObject* parent) virtual void ShowMembers(TMemberInspector& insp, char* parent) virtual Int_t Sizeof() const virtual void Streamer(TBuffer& b) void StreamerNVirtual(TBuffer& b) virtual Int_t WriteFile(Int_t cycle = 1)

Data Members

Int_t fVersion Key version identifier Int_t fNbytes Number of bytes for the object on file Int_t fObjlen Length of uncompressed object in bytes TDatime fDatime Date/Time of insertion in file Short_t fKeylen Number of bytes for the key itself Short_t fCycle Cycle number Seek_t fSeekKey Location of object on file Seek_t fSeekPdir Location of parent directory on file TString fClassName Object Class name Int_t fLeft Number of bytes left in current segment char* fBuffer Object buffer TBuffer* fBufferRef Pointer to the TBuffer object

See also


Class Description

  The TKey class includes functions to book space on a file,          
   to create I/O buffers, to fill these buffers                       
   to compress/uncompress data buffers.                               
  Before saving (making persistent) an object on a file, a key must   
  be created. The key structure contains all the information to       
  uniquely identify a persistent object on a file.                    
     fNbytes    = number of bytes for the compressed object+key       
     fObjlen    = Length of uncompressed object                       
     fDatime    = Date/Time when the object was written               
     fKeylen    = number of bytes for the key structure               
     fCycle     = cycle number of the object                          
     fSeekKey   = Address of the object on file (points to fNbytes)   
                  This is a redundant information used to cross-check 
                  the data base integrity.                            
     fSeekPdir  = Pointer to the directory supporting this object     
     fClassName = Object class name                                   
     fName      = name of the object                                  
     fTitle     = title of the object                                 
  The TKey class is used by ROOT to:                                  
    - to write an object in the Current Directory                     
    - to write a new ntuple buffer                                    
  The structure of a file is shown in TFile::TFile                    
  The structure of a directory is shown in TDirectory::TDirectory     
  The TKey class is used by the TBasket class                         
     See also TTree                                                   

TKey() : TNamed(), fDatime((UInt_t)0)
*-*-*-*-*-*-*-*-*-*-*TKey default constructor*-*-*-*-*-*-*-*-*-*-*-*-*
*-*                  ========================

TKey(Seek_t pointer, Int_t nbytes) : TNamed()
*-*-*-*-*-*-*-*-*-*-*-*-*Create a TKey object to read keys*-*-*-*-*-*-*-*
*-*                      =================================
  Constructor called by TDirectory::ReadKeys and by TFile::TFile
  A TKey object is created to read the keys structure itself

TKey(const char *name, const char *title, TClass *cl, Int_t nbytes) : TNamed(name,title)

TKey(const TString &name, const TString &title, TClass *cl, Int_t nbytes) : TNamed(name,title)

TKey(TObject *obj, const char *name, Int_t bufsize) : TNamed(name, obj->GetTitle())
*-*-*-*-*-*-*-*-*-*Create a TKey object and fill output buffer*-*-*-*-*-*-*
*-*                ===========================================

void Browse(TBrowser *b)
 Read object from disk and call its Browse() method.
 If object with same name already exist in memory delete it (like
 TDirectory::Get() is doing), except when the key references a
 folder in which case we don't want to re-read the folder object
 since it might contain new objects not yet saved.

void Create(Int_t nbytes)
*-*-*-*-*-*-*-*-*-*-*-*-*Create a TKey object *-*-*-*-*-*-*-*-*-*-*-*-*-*
*-*                      ====================

*-*-*-*-*-*-*-*-*-*-*TKey default destructor*-*-*-*-*-*-*-*-*-*-*-*-*
*-*                  =======================

void Delete(Option_t *option)
*-*-*-*-*-*-*-*-*-*-*-*Delete an object from the file*-*-*-*-*-*-*-*-*-*-*
*-*                    ==============================
 Note: the key is not deleted. You still have to call "delete key".
 This is different from the behaviour of TObject::Delete()!

void DeleteBuffer()
*-*-*-*-*-*-*-*-*-*-*-*Delete key buffer(s)*-*-*-*-*-*-*-*-*-*-*-*-*-*-*
*-*                    ====================

Short_t GetCycle() const
*-*-*-*-*-*-*-*-*-*-*-*-*Return cycle number associated to this key*-*-*-*
*-*                      ==========================================

Short_t GetKeep() const
*-*-*-*-*-*-*-*-*-*-*-*-*Returns the "KEEP" status*-*-*-*-*-*-*-*-*-*-*-*
*-*                      =========================

void FillBuffer(char *&buffer)
*-*-*-*-*-*-*-*-*-*-*-*Encode key header into output buffer-*-*-*-*-*-*-*
*-*                    ====================================

ULong_t Hash() const
 This Hash function should redefine the default from TNamed

Bool_t IsFolder() const

void Keep()
*-*-*-*-*-*-*-*-*-*-*-*-*Set the "KEEP" status*-*-*-*-*-*-*-*-*-*-*-*-*-*
*-*                      =====================
 When the KEEP flag is set to 1 the object cannot be purged

void ls(Option_t *) const
*-*-*-*-*-*-*-*-*-*-*-*-*List Key contents-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*
*-*                      =================

void Print(Option_t *) const
*-*-*-*-*-*-*-*-*-*-*-*-*Print key contents*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*
*-*                      ==================

TObject* ReadObj()
*-*-*-*-*-*-*-*-*-*-*-*-*To read an object from the file*-*-*-*-*-*-*-*-*
*-*                      ===============================
  The object associated to this key is read from the file into memory
  Once the key structure is read (via Streamer) the class identifier
  of the object is known.
  Using the class identifier we find the TClass object for this class.
  A TClass object contains a full description (i.e. dictionary) of the
  associated class. In particular the TClass object can create a new
  object of the class type it describes. This new object now calls its
  Streamer function to rebuilt itself.

  In case the class of this object derives from TObject but not
  as a first inheritance, one must cast the return value twice.
  Example1: Normal case:
      class MyClass : public TObject, public AnotherClass
   then on return, one can do:
    MyClass *obj = (MyClass*)key->ReadObj();

  Example2: Special case:
      class MyClass : public AnotherClass, public TObject
   then on return, one must do:
    MyClass *obj = dynamic_cast<MyClass*>(key->ReadObj();

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

Int_t Read(TObject *obj)
*-*-*-*-*-*-*-*-*-*-*-*-*To read an object from the file*-*-*-*-*-*-*-*-*
*-*                      ===============================
  The object associated to this key is read from the file into memory
  Before invoking this function, obj has been created via the
  default constructor.

void ReadBuffer(char *&buffer)
*-*-*-*-*-*-*-*-*-*-*-*Decode input buffer-*-*-*-*-*-*-*-*-*-*-*-*-*-*
*-*                    ===================

void ReadFile()
*-*-*-*-*-*-*-*-*-*-*-*-*Read the key structure from the file-*-*-*-*-*-*
*-*                      ====================================

void SetParent(TObject *parent)
  Set parent in key buffer

Int_t Sizeof() const
*-*-*-*-*-*-*-*Return the size in bytes of the key header structure*-*-*-*

void Streamer(TBuffer &b)
*-*-*-*-*-*-*-*-*Stream a class object*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*
*-*              =========================================

Int_t WriteFile(Int_t cycle)
*-*-*-*-*-*-*-*-*-*-*Write the encoded object supported by this key*-*-*-*
*-*                  ==============================================

Inline Functions

        const char* GetClassName() const
              char* GetBuffer() const
           TBuffer* GetBufferRef() const
              Int_t GetKeylen() const
              Int_t GetNbytes() const
              Int_t GetObjlen() const
              Int_t GetVersion() const
             Seek_t GetSeekKey() const
             Seek_t GetSeekPdir() const
              Int_t Read(TObject* obj)
               void SetBuffer()
            TClass* Class()
            TClass* IsA() const
               void ShowMembers(TMemberInspector& insp, char* parent)
               void StreamerNVirtual(TBuffer& b)
               TKey TKey(const TKey&)

Author: Rene Brun 28/12/94
Last update: root/base:$Name: $:$Id: TKey.cxx,v 1.22 2002/08/23 08:54:38 brun Exp $
Copyright (C) 1995-2000, Rene Brun and Fons Rademakers. *

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