TKey

class TKey : public TNamed

    protected:

      virtual void Create(Int_t nbytes)
      virtual void Read(Text_t* name)

    public:

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

  Data Members

    protected:

         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

TBasket

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

*-*-*-*-*-*-*-*-*-*-*-*-*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

*-*-*-*-*-*-*-*-*-*Create a TKey object and fill output buffer*-*-*-*-*-*-*
*-*                ===========================================

 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.

*-*-*-*-*-*-*-*-*-*-*-*-*Create a TKey object *-*-*-*-*-*-*-*-*-*-*-*-*-*
*-*                      ====================

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

*-*-*-*-*-*-*-*-*-*-*-*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()!

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

*-*-*-*-*-*-*-*-*-*-*-*-*Return cycle number associated to this key*-*-*-*
*-*                      ==========================================

*-*-*-*-*-*-*-*-*-*-*-*-*Returns the "KEEP" status*-*-*-*-*-*-*-*-*-*-*-*
*-*                      =========================

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

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

*-*-*-*-*-*-*-*-*-*-*-*-*List Key contents-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*
*-*                      =================

*-*-*-*-*-*-*-*-*-*-*-*-*Print key contents*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*
*-*                      ==================

*-*-*-*-*-*-*-*-*-*-*-*-*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.

*-*-*-*-*-*-*-*-*-*-*-*-*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.

*-*-*-*-*-*-*-*-*-*-*-*Decode input buffer-*-*-*-*-*-*-*-*-*-*-*-*-*-*
*-*                    ===================

*-*-*-*-*-*-*-*-*-*-*-*-*Read the key structure from the file-*-*-*-*-*-*
*-*                      ====================================

*-*-*-*-*-*-*-*Return the size in bytes of the key header structure*-*-*-*
*-*-*-*-*-*-*-*====================================================

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

*-*-*-*-*-*-*-*-*-*-*Write the encoded object supported by this key*-*-*-*
*-*                  ==============================================

Inline Functions

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