Book space in a file, create I/O buffers, to fill them, (un)compress them.

The TKey class includes functions to book space in a file, to create I/O buffers, to fill these buffers, to compress/uncompress data buffers. Before saving (making persistent) an object in a file, a key must be created. The key structure contains all the information to uniquely identify a persistent object in a file.

Data Member	Explanation
fNbytes	Number of bytes for the compressed object and 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.

In the 16 highest bits of fSeekPdir is encoded a pid offset. This offset is to be added to the pid index stored in the TRef object and the referenced TObject.

The TKey class is used by ROOT to:

Write an object in the current directory
Write a new ntuple buffer

The structure of a file is shown in TFile::TFile. The structure of a directory is shown in TDirectoryFile::TDirectoryFile. The TKey class is used by the TBasket class. See also TTree.

Definition at line 24 of file TKey.h.

Public Member Functions
	TKey ()
	TKey default constructor. More...

	TKey (TDirectory *motherDir)
	TKey default constructor. More...

	TKey (TDirectory *motherDir, const TKey &orig, UShort_t pidOffset)
	Copy a TKey from its original directory to the new 'motherDir'. More...

	TKey (const char name, const char title, const TClass cl, Int_t nbytes, TDirectory motherDir)
	Create a TKey object with the specified name, title for the given class. More...

	TKey (const TString &name, const TString &title, const TClass cl, Int_t nbytes, TDirectory motherDir)
	Create a TKey object with the specified name, title for the given class. More...

	TKey (const TObject obj, const char name, Int_t bufsize, TDirectory *motherDir)
	Create a TKey object for a TObject* and fill output buffer. More...

	TKey (const void obj, const TClass cl, const char name, Int_t bufsize, TDirectory motherDir)
	Create a TKey object for any object obj of class cl d and fill output buffer. More...

	TKey (Long64_t pointer, Int_t nbytes, TDirectory *motherDir=0)
	Create a TKey object to read keys. More...

virtual	~TKey ()
	TKey default destructor. More...

virtual void	Browse (TBrowser *b)
	Read object from disk and call its Browse() method. More...

virtual void	Delete (Option_t *option="")
	Delete an object from the file. More...

virtual void	DeleteBuffer ()
	Delete key buffer(s). More...

virtual void	FillBuffer (char *&buffer)
	Encode key header into output buffer. More...

virtual char *	GetBuffer () const

TBuffer *	GetBufferRef () const

virtual const char *	GetClassName () const

Short_t	GetCycle () const
	Return cycle number associated to this key. More...

const TDatime &	GetDatime () const

TFile *	GetFile () const
	Returns file to which key belong. More...

virtual const char *	GetIconName () const
	Title can keep 32x32 xpm thumbnail/icon of the parent object. More...

Short_t	GetKeep () const
	Returns the "KEEP" status. More...

Int_t	GetKeylen () const

TDirectory *	GetMotherDir () const

Int_t	GetNbytes () const

Int_t	GetObjlen () const

virtual Long64_t	GetSeekKey () const

virtual Long64_t	GetSeekPdir () const

virtual const char *	GetTitle () const
	Returns title (title can contain 32x32 xpm thumbnail/icon). More...

Int_t	GetVersion () const

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

virtual void	IncrementPidOffset (UShort_t offset)
	Increment fPidOffset by 'offset'. More...

Bool_t	IsFolder () const
	Check if object referenced by the key is a folder. More...

virtual void	Keep ()
	Set the "KEEP" status. More...

virtual void	ls (Option_t *option="") const
	List Key contents. More...

virtual void	Print (Option_t *option="") const
	Print key contents. More...

virtual Int_t	Read (TObject *obj)
	To read an object from the file. More...

virtual void	ReadBuffer (char *&buffer)
	Decode input buffer. More...

virtual Bool_t	ReadFile ()
	Read the key structure from the file. More...

void	ReadKeyBuffer (char *&buffer)
	Decode input buffer. More...

virtual TObject *	ReadObj ()
	To read a TObject* from the file. More...

virtual void *	ReadObjectAny (const TClass *expectedClass)
	To read an object (non deriving from TObject) from the file. More...

virtual TObject *	ReadObjWithBuffer (char *bufferRead)
	To read a TObject* from bufferRead. More...

virtual void	SetBuffer ()

void	SetMotherDir (TDirectory *dir)

virtual void	SetParent (const TObject *parent)
	Set parent in key buffer. More...

virtual Int_t	Sizeof () const
	Return the size in bytes of the key header structure. More...

virtual Int_t	WriteFile (Int_t cycle=1, TFile *f=0)
	Write the encoded object supported by this key. More...

Public Member Functions inherited from TNamed
	TNamed ()

	TNamed (const char name, const char title)

	TNamed (const TString &name, const TString &title)

	TNamed (const TNamed &named)
	TNamed copy ctor. More...

virtual	~TNamed ()

virtual void	Clear (Option_t *option="")
	Set name and title to empty strings (""). More...

virtual TObject *	Clone (const char *newname="") const
	Make a clone of an object using the Streamer facility. More...

virtual Int_t	Compare (const TObject *obj) const
	Compare two TNamed objects. More...

virtual void	Copy (TObject &named) const
	Copy this to obj. More...

virtual const char *	GetName () const
	Returns name of object. More...

virtual Bool_t	IsSortable () const

TNamed &	operator= (const TNamed &rhs)
	TNamed assignment operator. More...

virtual void	SetName (const char *name)
	Set the name of the TNamed. More...

virtual void	SetNameTitle (const char name, const char title)
	Set all the TNamed parameters (name and title). More...

virtual void	SetTitle (const char *title="")
	Set the title of the TNamed. More...

Public Member Functions inherited from TObject
	TObject ()
	TObject constructor. More...

	TObject (const TObject &object)
	TObject copy ctor. More...

virtual	~TObject ()
	TObject destructor. More...

void	AbstractMethod (const char *method) const
	Use this method to implement an "abstract" method that you don't want to leave purely abstract. More...

virtual void	AppendPad (Option_t *option="")
	Append graphics object to current pad. More...

virtual const char *	ClassName () const
	Returns name of class to which the object belongs. More...

virtual Int_t	DistancetoPrimitive (Int_t px, Int_t py)
	Computes distance from point (px,py) to the object. More...

virtual void	Draw (Option_t *option="")
	Default Draw method for all objects. More...

virtual void	DrawClass () const
	Draw class inheritance tree of the class to which this object belongs. More...

virtual TObject *	DrawClone (Option_t *option="") const
	Draw a clone of this object in the current selected pad for instance with: `gROOT->SetSelectedPad(gPad)`. More...

virtual void	Dump () const
	Dump contents of object on stdout. More...

virtual void	Error (const char method, const char msgfmt,...) const
	Issue error message. More...

virtual void	Execute (const char method, const char params, Int_t *error=0)
	Execute method on this object with the given parameter string, e.g. More...

virtual void	Execute (TMethod method, TObjArray params, Int_t *error=0)
	Execute method on this object with parameters stored in the TObjArray. More...

virtual void	ExecuteEvent (Int_t event, Int_t px, Int_t py)
	Execute action corresponding to an event at (px,py). More...

virtual void	Fatal (const char method, const char msgfmt,...) const
	Issue fatal error message. More...

virtual TObject *	FindObject (const char *name) const
	Must be redefined in derived classes. More...

virtual TObject *	FindObject (const TObject *obj) const
	Must be redefined in derived classes. More...

virtual Option_t *	GetDrawOption () const
	Get option used by the graphics system to draw this object. More...

virtual char *	GetObjectInfo (Int_t px, Int_t py) const
	Returns string containing info about the object at position (px,py). More...

virtual Option_t *	GetOption () const

virtual UInt_t	GetUniqueID () const
	Return the unique object id. More...

virtual Bool_t	HandleTimer (TTimer *timer)
	Execute action in response of a timer timing out. More...

virtual void	Info (const char method, const char msgfmt,...) const
	Issue info message. More...

virtual Bool_t	InheritsFrom (const char *classname) const
	Returns kTRUE if object inherits from class "classname". More...

virtual Bool_t	InheritsFrom (const TClass *cl) const
	Returns kTRUE if object inherits from TClass cl. More...

virtual void	Inspect () const
	Dump contents of this object in a graphics canvas. More...

void	InvertBit (UInt_t f)

virtual Bool_t	IsEqual (const TObject *obj) const
	Default equal comparison (objects are equal if they have the same address in memory). More...

Bool_t	IsOnHeap () const

Bool_t	IsZombie () const

void	MayNotUse (const char *method) const
	Use this method to signal that a method (defined in a base class) may not be called in a derived class (in principle against good design since a child class should not provide less functionality than its parent, however, sometimes it is necessary). More...

virtual Bool_t	Notify ()
	This method must be overridden to handle object notification. More...

void	Obsolete (const char method, const char asOfVers, const char *removedFromVers) const
	Use this method to declare a method obsolete. More...

void	operator delete (void *ptr)
	Operator delete. More...

void	operator delete[] (void *ptr)
	Operator delete []. More...

void *	operator new (size_t sz)

void *	operator new (size_t sz, void *vp)

void *	operator new[] (size_t sz)

void *	operator new[] (size_t sz, void *vp)

TObject &	operator= (const TObject &rhs)
	TObject assignment operator. More...

virtual void	Paint (Option_t *option="")
	This method must be overridden if a class wants to paint itself. More...

virtual void	Pop ()
	Pop on object drawn in a pad to the top of the display list. More...

virtual void	RecursiveRemove (TObject *obj)
	Recursively remove this object from a list. More...

void	ResetBit (UInt_t f)

virtual void	SaveAs (const char filename="", Option_t option="") const
	Save this object in the file specified by filename. More...

virtual void	SavePrimitive (std::ostream &out, Option_t *option="")
	Save a primitive as a C++ statement(s) on output stream "out". More...

void	SetBit (UInt_t f, Bool_t set)
	Set or unset the user status bits as specified in f. More...

void	SetBit (UInt_t f)

virtual void	SetDrawOption (Option_t *option="")
	Set drawing option for object. More...

virtual void	SetUniqueID (UInt_t uid)
	Set the unique object id. More...

virtual void	SysError (const char method, const char msgfmt,...) const
	Issue system error message. More...

Bool_t	TestBit (UInt_t f) const

Int_t	TestBits (UInt_t f) const

virtual void	UseCurrentStyle ()
	Set current style settings in this object This function is called when either TCanvas::UseCurrentStyle or TROOT::ForceStyle have been invoked. More...

virtual void	Warning (const char method, const char msgfmt,...) const
	Issue warning message. More...

virtual Int_t	Write (const char *name=0, Int_t option=0, Int_t bufsize=0)
	Write this object to the current directory. More...

virtual Int_t	Write (const char *name=0, Int_t option=0, Int_t bufsize=0) const
	Write this object to the current directory. More...

Protected Member Functions
void	Build (TDirectory motherDir, const char classname, Long64_t filepos)
	Method used in all TKey constructor to initialize basic data fields. More...

virtual void	Create (Int_t nbytes, TFile *f=0)
	Create a TKey object of specified size. More...

virtual Int_t	Read (const char *name)
	Read contents of object with specified name from the current directory. More...

virtual void	Reset ()
	Reset the key as it had not been 'filled' yet. More...

virtual Int_t	WriteFileKeepBuffer (TFile *f=0)
	Write the encoded object supported by this key. More...

Protected Member Functions inherited from TObject
virtual void	DoError (int level, const char location, const char fmt, va_list va) const
	Interface to ErrorHandler (protected). More...

void	MakeZombie ()

Protected Attributes
char *	fBuffer
	Object buffer. More...

TBuffer *	fBufferRef
	Pointer to the TBuffer object. More...

TString	fClassName
	Object Class name. More...

Short_t	fCycle
	Cycle number. More...

TDatime	fDatime
	Date/Time of insertion in file. More...

Short_t	fKeylen
	Number of bytes for the key itself. More...

Int_t	fLeft
	Number of bytes left in current segment. More...

TDirectory *	fMotherDir
	!pointer to mother directory More...

Int_t	fNbytes
	Number of bytes for the object on file. More...

Int_t	fObjlen
	Length of uncompressed object in bytes. More...

UShort_t	fPidOffset
	!Offset to be added to the pid index in this key/buffer. This is actually saved in the high bits of fSeekPdir More...

Long64_t	fSeekKey
	Location of object on file. More...

Long64_t	fSeekPdir
	Location of parent directory on file. More...

Int_t	fVersion
	Key version identifier. More...

Protected Attributes inherited from TNamed
TString	fName

TString	fTitle

Private Types
enum	EStatusBits { kIsDirectoryFile = BIT(14) }

Private Member Functions
	TKey (const TKey &)

TKey &	operator= (const TKey &)

Additional Inherited Members
Public Types inherited from TObject
enum	{ kIsOnHeap = 0x01000000, kNotDeleted = 0x02000000, kZombie = 0x04000000, kBitMask = 0x00ffffff }

enum	{ kSingleKey = BIT(0), kOverwrite = BIT(1), kWriteDelete = BIT(2) }

enum	EStatusBits { kCanDelete = BIT(0), kMustCleanup = BIT(3), kObjInCanvas = BIT(3), kIsReferenced = BIT(4), kHasUUID = BIT(5), kCannotPick = BIT(6), kNoContextMenu = BIT(8), kInvalidObject = BIT(13) }

Static Public Member Functions inherited from TObject
static Long_t	GetDtorOnly ()
	Return destructor only flag. More...

static Bool_t	GetObjectStat ()
	Get status of object stat flag. More...

static void	SetDtorOnly (void *obj)
	Set destructor only flag. More...

static void	SetObjectStat (Bool_t stat)
	Turn on/off tracking of objects in the TObjectTable. More...

#include <TKey.h>

Inheritance diagram for TKey:

[legend]

Member Enumeration Documentation

◆ EStatusBits

enum TKey::EStatusBits

private

Enumerator
kIsDirectoryFile

Definition at line 27 of file TKey.h.

Constructor & Destructor Documentation

◆ TKey() [1/9]

TKey::TKey ( const TKey & )

private

◆ TKey() [2/9]

TKey::TKey ( )

TKey default constructor.

Definition at line 92 of file TKey.cxx.

◆ TKey() [3/9]

TKey::TKey ( TDirectory * motherDir )

TKey default constructor.

Definition at line 104 of file TKey.cxx.

◆ TKey() [4/9]

TKey::TKey	(	TDirectory *	motherDir,
		const TKey &	orig,
		UShort_t	pidOffset
	)

Copy a TKey from its original directory to the new 'motherDir'.

Definition at line 116 of file TKey.cxx.

◆ TKey() [5/9]

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

Create a TKey object with the specified name, title for the given class.

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

Definition at line 196 of file TKey.cxx.

◆ TKey() [6/9]

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

Create a TKey object with the specified name, title for the given class.

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

Definition at line 212 of file TKey.cxx.

◆ TKey() [7/9]

TKey::TKey	(	const TObject *	obj,
		const char *	name,
		Int_t	bufsize,
		TDirectory *	motherDir
	)

Create a TKey object for a TObject* and fill output buffer.

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

Definition at line 228 of file TKey.cxx.

◆ TKey() [8/9]

TKey::TKey	(	const void *	obj,
		const TClass *	cl,
		const char *	name,
		Int_t	bufsize,
		TDirectory *	motherDir
	)

Create a TKey object for any object obj of class cl d and fill output buffer.

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

Definition at line 301 of file TKey.cxx.

◆ TKey() [9/9]

TKey::TKey	(	Long64_t	pointer,
		Int_t	nbytes,
		TDirectory *	motherDir = `0`
	)

Create a TKey object to read keys.

Constructor called by TDirectoryFile::ReadKeys and by TFile::TFile. A TKey object is created to read the keys structure itself.

Definition at line 180 of file TKey.cxx.

◆ ~TKey()

TKey::~TKey ( )

virtual

TKey default destructor.

Definition at line 520 of file TKey.cxx.

Member Function Documentation

◆ Browse()

void TKey::Browse ( TBrowser * b )

virtual

Read object from disk and call its Browse() method.

If object with same name already exist in memory delete it (like TDirectoryFile::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.

Reimplemented from TObject.

Definition at line 426 of file TKey.cxx.

◆ Build()

void TKey::Build	(	TDirectory *	motherDir,
		const char *	classname,
		Long64_t	filepos
	)

protected

Method used in all TKey constructor to initialize basic data fields.

The member filepos is used to calculate correct version number of key if filepos==-1, end of file position is used.

Definition at line 391 of file TKey.cxx.

◆ Create()

void TKey::Create	(	Int_t	nbytes,
		TFile *	externFile = `0`
	)

protectedvirtual

Create a TKey object of specified size.

If externFile!=0, key will be allocated in specified file, otherwise file of mother directory will be used.

Definition at line 458 of file TKey.cxx.

◆ Delete()

void TKey::Delete ( Option_t * option = "" )

virtual

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()!

Reimplemented from TObject.

Reimplemented in TKeySQL, and TKeyXML.

Definition at line 534 of file TKey.cxx.

◆ DeleteBuffer()

void TKey::DeleteBuffer ( )

virtual

Delete key buffer(s).

Reimplemented in TKeySQL, and TKeyXML.

Definition at line 546 of file TKey.cxx.

◆ FillBuffer()

void TKey::FillBuffer ( char *& buffer )

virtual

Encode key header into output buffer.

Reimplemented from TNamed.

Reimplemented in TKeySQL, and TKeyXML.

Definition at line 588 of file TKey.cxx.

◆ GetBuffer()

virtual char* TKey::GetBuffer ( ) const

inlinevirtual

Reimplemented in TKeySQL, and TKeyXML.

Definition at line 74 of file TKey.h.

◆ GetBufferRef()

TBuffer* TKey::GetBufferRef ( ) const

inline

Definition at line 75 of file TKey.h.

◆ GetClassName()

virtual const char* TKey::GetClassName ( ) const

inlinevirtual

Definition at line 71 of file TKey.h.

◆ GetCycle()

Short_t TKey::GetCycle ( ) const

Return cycle number associated to this key.

Definition at line 564 of file TKey.cxx.

◆ GetDatime()

const TDatime& TKey::GetDatime ( ) const

inline

Definition at line 77 of file TKey.h.

◆ GetFile()

TFile * TKey::GetFile ( ) const

Returns file to which key belong.

Definition at line 572 of file TKey.cxx.

◆ GetIconName()

const char * TKey::GetIconName ( ) const

virtual

Title can keep 32x32 xpm thumbnail/icon of the parent object.

Reimplemented from TObject.

Definition at line 1517 of file TKey.cxx.

◆ GetKeep()

Short_t TKey::GetKeep ( ) const

Returns the "KEEP" status.

Definition at line 580 of file TKey.cxx.

◆ GetKeylen()

Int_t TKey::GetKeylen ( ) const

inline

Definition at line 80 of file TKey.h.

◆ GetMotherDir()

TDirectory* TKey::GetMotherDir ( ) const

inline

Definition at line 81 of file TKey.h.

◆ GetNbytes()

Int_t TKey::GetNbytes ( ) const

inline

Definition at line 82 of file TKey.h.

◆ GetObjlen()

Int_t TKey::GetObjlen ( ) const

inline

Definition at line 83 of file TKey.h.

◆ GetSeekKey()

virtual Long64_t TKey::GetSeekKey ( ) const

inlinevirtual

Reimplemented in TKeySQL, and TKeyXML.

Definition at line 85 of file TKey.h.

◆ GetSeekPdir()

virtual Long64_t TKey::GetSeekPdir ( ) const

inlinevirtual

Reimplemented in TKeySQL, and TKeyXML.

Definition at line 86 of file TKey.h.

◆ GetTitle()

const char * TKey::GetTitle ( ) const

virtual

Returns title (title can contain 32x32 xpm thumbnail/icon).

Reimplemented from TNamed.

Definition at line 1525 of file TKey.cxx.

◆ GetVersion()

Int_t TKey::GetVersion ( ) const

inline

Definition at line 84 of file TKey.h.

◆ Hash()

ULong_t TKey::Hash ( ) const

virtual

This Hash function should redefine the default from TNamed.

Reimplemented from TNamed.

Definition at line 627 of file TKey.cxx.

◆ IncrementPidOffset()

void TKey::IncrementPidOffset ( UShort_t offset )

virtual

Increment fPidOffset by 'offset'.

This offset is used when a key (or basket) is transfered from one file to the other. In this case the TRef and TObject might have stored a pid index (to retrieve TProcessIDs) which refered to their order on the original file, the fPidOffset is to be added to those values to correctly find the TProcessID. This fPidOffset needs to be increment if the key/basket is copied and need to be zero for new key/basket.

Definition at line 642 of file TKey.cxx.

◆ IsFolder()

Bool_t TKey::IsFolder ( ) const

virtual

Check if object referenced by the key is a folder.

Reimplemented from TObject.

Definition at line 656 of file TKey.cxx.

◆ Keep()

void TKey::Keep ( )

virtual

Set the "KEEP" status.

When the KEEP flag is set to 1 the object cannot be purged.

Reimplemented in TKeySQL, and TKeyXML.

Definition at line 677 of file TKey.cxx.

◆ ls()

void TKey::ls ( Option_t * option = "" ) const

virtual

List Key contents.

Reimplemented from TNamed.

Definition at line 685 of file TKey.cxx.

◆ operator=()

TKey& TKey::operator= ( const TKey & )

private

◆ Print()

void TKey::Print ( Option_t * option = "" ) const

virtual

Print key contents.

Reimplemented from TNamed.

Definition at line 694 of file TKey.cxx.

◆ Read() [1/2]

virtual Int_t TKey::Read ( const char * name )

inlineprotectedvirtual

Read contents of object with specified name from the current directory.

First the key with the given name 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().

Reimplemented from TObject.

Reimplemented in TKeyXML, and TKeySQL.

Definition at line 49 of file TKey.h.

◆ Read() [2/2]

Int_t TKey::Read ( TObject * obj )

virtual

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.

Reimplemented in TKeySQL, and TKeyXML.

Definition at line 1146 of file TKey.cxx.

◆ ReadBuffer()

void TKey::ReadBuffer ( char *& buffer )

virtual

Decode input buffer.

In some situation will add key to gDirectory.

Reimplemented in TKeySQL, and TKeyXML.

Definition at line 1206 of file TKey.cxx.

◆ ReadFile()

Bool_t TKey::ReadFile ( )

virtual

Read the key structure from the file.

Reimplemented in TKeySQL, and TKeyXML.

Definition at line 1261 of file TKey.cxx.

◆ ReadKeyBuffer()

void TKey::ReadKeyBuffer ( char *& buffer )

Decode input buffer.

Definition at line 1218 of file TKey.cxx.

◆ ReadObj()

TObject * TKey::ReadObj ( )

virtual

To read a TObject* 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.

Use TKey::ReadObjectAny to read any object non-derived from TObject

Note

A C style cast can only be used in the case where the final class of this object derives from TObject as a first inheritance, otherwise one must use a dynamic_cast.

Example1: simplified case

class MyClass : public TObject, public AnotherClass then on return, one get away with using: MyClass obj = (MyClass)key->ReadObj();

Example2: Usual case (recommended unless performance is critical)

MyClass obj = dynamic_cast<MyClass>(key->ReadObj()); which support also the more complex inheritance like: class MyClass : public AnotherClass, public TObject

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

Reimplemented in TKeySQL, and TKeyXML.

Definition at line 730 of file TKey.cxx.

◆ ReadObjectAny()

void * TKey::ReadObjectAny ( const TClass * expectedClass )

virtual

To read an object (non deriving from TObject) from the file.

If expectedClass is not null, we checked that that actual class of the object stored is suitable to be stored in a pointer pointing to an object of class 'expectedClass'. We also adjust the value of the returned address so that it is suitable to be cast (C-Style) a pointer pointing to an object of class 'expectedClass'.

So for example if the class Bottom inherits from Top and the object stored is of type Bottom you can safely do:

auto TopClass = TClass::GetClass("Top");
auto ptr = (Top*) key->ReadObjectAny( TopClass );
if (ptr==0) printError("the object stored in the key is not of the expected type\n");

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.

Reimplemented in TKeySQL, and TKeyXML.

Definition at line 1008 of file TKey.cxx.

◆ ReadObjWithBuffer()

TObject * TKey::ReadObjWithBuffer ( char * bufferRead )

virtual

To read a TObject* from bufferRead.

This function is identical to TKey::ReadObj, but it reads directly from bufferRead instead of reading from a file. The object associated to this key is read from the buffer into memory 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.

Note

This function is called only internally by ROOT classes. Although being public it is not supposed to be used outside ROOT. If used, you must make sure that the bufferRead is large enough to accomodate the object being read.

Reimplemented in TKeySQL, and TKeyXML.

Definition at line 872 of file TKey.cxx.

◆ Reset()

void TKey::Reset ( void )

protectedvirtual

Reset the key as it had not been 'filled' yet.

Reimplemented in TBasket, and TBasketSQL.

Definition at line 1298 of file TKey.cxx.

◆ SetBuffer()

virtual void TKey::SetBuffer ( )

inlinevirtual

Reimplemented in TKeySQL, and TKeyXML.

Definition at line 100 of file TKey.h.

◆ SetMotherDir()

void TKey::SetMotherDir ( TDirectory * dir )

inline

Definition at line 102 of file TKey.h.

◆ SetParent()

void TKey::SetParent ( const TObject * parent )

virtual

Set parent in key buffer.

Definition at line 1290 of file TKey.cxx.

◆ Sizeof()

Int_t TKey::Sizeof ( ) const

virtual

Return the size in bytes of the key header structure.

An explaination about the nbytes (Int_t nbytes) variable used in the function. The size of fSeekKey and fSeekPdir is 8 instead of 4 if version is greater than 1000.

Component	Sizeof
fNbytes	4
sizeof(Version_t)	2
fObjlen	4
fKeylen	2
fCycle	2
fSeekKey	4 or 8
fSeekPdir	4 or 8
TOTAL	22

Reimplemented from TNamed.

Definition at line 1332 of file TKey.cxx.

◆ WriteFile()

Int_t TKey::WriteFile	(	Int_t	cycle = `1`,
		TFile *	f = `0`
	)

virtual

Write the encoded object supported by this key.

The function returns the number of bytes committed to the file. If a write error occurs, the number of bytes returned is -1.

Reimplemented in TKeySQL, and TKeyXML.

Definition at line 1443 of file TKey.cxx.

◆ WriteFileKeepBuffer()

Int_t TKey::WriteFileKeepBuffer ( TFile * f = 0 )

protectedvirtual

Write the encoded object supported by this key.

The function returns the number of bytes committed to the file. If a write error occurs, the number of bytes returned is -1.

Definition at line 1484 of file TKey.cxx.

Member Data Documentation

◆ fBuffer

char* TKey::fBuffer

protected

Object buffer.

Definition at line 44 of file TKey.h.

◆ fBufferRef

TBuffer* TKey::fBufferRef

protected

Pointer to the TBuffer object.

Definition at line 45 of file TKey.h.

◆ fClassName

TString TKey::fClassName

protected

Object Class name.

Definition at line 42 of file TKey.h.

◆ fCycle

Short_t TKey::fCycle

protected

Cycle number.

Definition at line 39 of file TKey.h.

◆ fDatime

TDatime TKey::fDatime

protected

Date/Time of insertion in file.

Definition at line 37 of file TKey.h.

◆ fKeylen

Short_t TKey::fKeylen

protected

Number of bytes for the key itself.

Definition at line 38 of file TKey.h.

◆ fLeft

Int_t TKey::fLeft

protected

Number of bytes left in current segment.

Definition at line 43 of file TKey.h.

◆ fMotherDir

TDirectory* TKey::fMotherDir

protected

!pointer to mother directory

Definition at line 47 of file TKey.h.

◆ fNbytes

Int_t TKey::fNbytes

protected

Number of bytes for the object on file.

Definition at line 35 of file TKey.h.

◆ fObjlen

Int_t TKey::fObjlen

protected

Length of uncompressed object in bytes.

Definition at line 36 of file TKey.h.

◆ fPidOffset

UShort_t TKey::fPidOffset

protected

!Offset to be added to the pid index in this key/buffer. This is actually saved in the high bits of fSeekPdir

Definition at line 46 of file TKey.h.

◆ fSeekKey

Long64_t TKey::fSeekKey

protected

Location of object on file.

Definition at line 40 of file TKey.h.

◆ fSeekPdir

Long64_t TKey::fSeekPdir

protected

Location of parent directory on file.

Definition at line 41 of file TKey.h.

◆ fVersion

Int_t TKey::fVersion

protected

Key version identifier.

Definition at line 34 of file TKey.h.

The documentation for this class was generated from the following files:

io/io/inc/TKey.h
io/io/src/TKey.cxx

Public Member Functions

Protected Member Functions

Protected Attributes

Private Types

Private Member Functions

Additional Inherited Members

Member Enumeration Documentation

◆ EStatusBits

Constructor & Destructor Documentation

◆ TKey() [1/9]

◆ TKey() [2/9]

◆ TKey() [3/9]

◆ TKey() [4/9]

◆ TKey() [5/9]

◆ TKey() [6/9]

◆ TKey() [7/9]

◆ TKey() [8/9]

◆ TKey() [9/9]

◆ ~TKey()

Member Function Documentation

◆ Browse()

◆ Build()

◆ Create()

◆ Delete()

◆ DeleteBuffer()

◆ FillBuffer()

◆ GetBuffer()

◆ GetBufferRef()

◆ GetClassName()

◆ GetCycle()

◆ GetDatime()

◆ GetFile()

◆ GetIconName()

◆ GetKeep()

◆ GetKeylen()

◆ GetMotherDir()

◆ GetNbytes()

◆ GetObjlen()

◆ GetSeekKey()

◆ GetSeekPdir()

◆ GetTitle()

◆ GetVersion()

◆ Hash()

◆ IncrementPidOffset()

◆ IsFolder()

◆ Keep()

◆ ls()

◆ operator=()

◆ Print()

◆ Read() [1/2]

◆ Read() [2/2]

◆ ReadBuffer()

◆ ReadFile()

◆ ReadKeyBuffer()

◆ ReadObj()

Note

Example1: simplified case

Example2: Usual case (recommended unless performance is critical)

◆ ReadObjectAny()

◆ ReadObjWithBuffer()

Note

◆ Reset()

◆ SetBuffer()

◆ SetMotherDir()

◆ SetParent()

◆ Sizeof()

◆ WriteFile()

◆ WriteFileKeepBuffer()

Member Data Documentation

◆ fBuffer

◆ fBufferRef

◆ fClassName

◆ fCycle

◆ fDatime

◆ fKeylen

◆ fLeft

◆ fMotherDir

◆ fNbytes

◆ fObjlen

◆ fPidOffset