HDF5 documents and links 
Introduction to HDF5 
HDF5 User’s Guide 
Other High-level API documents
In the HDF5 Reference Manual  
H5DS   H5IM   H5LT   H5PT   H5TB   Optimized 
H5   H5A   H5D   H5E   H5F   H5G   H5I  
H5L   H5O   H5P   H5R   H5S   H5T   H5Z  
Tools   Datatypes   Fortran  

H5PT: HDF5 Packet Table
C++ Wrappers


Classes: Functions (none are static; all must be called on an object):



Packet Table:
Name: Null Constructor
Signature:
PacketTable( )
Purpose:
Creates an invalid packet table object.
Description:
The object created with this call will return false if IsValid() is called on it. To create a valid packet table, use the FL_Packet_Table constructors. This function does not make any change to the underlying HDF5 file.


Name: “Open” Constructor
Signature:
PacketTable(hid_t fileID, const char* ptname)
PacketTable(hid_t fileID, char* ptname) (deprecated)
Purpose:
Opens an existing packet table.
Description:
Opens an existing packet table, named ptname, which can contain either fixed-length or variable-length packets.
Parameters:
hid_t fileID
IN: File or group in which the packet table is located
const char* ptname
IN: The packet table’s name
History:
Release Change
1.10.0 and 1.8.17     Function parameters were revised.


Name: Destructor
Signature:
~PacketTable()
Description:
The destructor closes the packet table in the file, so a packet table created or opened with the C++ wrapper does not need to be closed manually.


Name: IsValid
Signature:
bool IsValid()
Purpose:
Determines if this is a valid packet table.
Description:
This function is used to ensure that a PacketTable object corresponds to an open packet table in the file. It should be called after the constructor to check that there were no errors creating or opening the packet table.
Returns:
Returns true if this is an open packet table; otherwise returns false.


Name: IsVariableLength
Signature:
int IsVariableLength()
Purpose:
Determines if this is a valid packet table.
Description:
This function returns 1 if this packet table uses a variable-length datatype, 0 if not, and FAIL if failure occurs.
Returns:
Returns 1, 0, or FAIL.
History:
Release Change
1.10.0 and 1.8.17     Function introduced.


Name: ResetIndex
Signature:
void ResetIndex()
Purpose:
Resets the packet table’s index to point to the first packet.
Description:
A packet table keeps track of the user’s current location in the table so that the user can iterate through packets. This function should be called before using GetNextPacket.


Name: SetIndex
Signature:
int SetIndex(hsize_t index);
Purpose:
Sets a packet table’s current index.
Description:
This function allows the user to begin iterating through packets starting from any arbitrary index. Packet tables are zero-indexed, so packet 0 is the first packet.
Parameters:
hsize_t index
IN: The value to which the packet table’s index should be set
Returns:
Returns non-negative on success and negative on error.


Name: GetIndex
Signature:
hsize_t GetIndex(int& error);
Purpose:
Returns the position of the current packet.
Description:
This function allows the user to determine the position of the current packet.

If GetIndex returns 0 (zero), you must then check the value of the parameter error. If error is negative, GetIndex has failed; if error is 0 (zero), the position of the current packet is 0 (zero).

Parameters:
int& error (optional)
OUT: Non-negative if index was successfully retrieved, negative on failure.
Returns:
Returns the position of the current packet on success and 0 (zero) on error.


Name: GetPacketCount
Signatures:
hsize_t GetPacketCount()
hsize_t GetPacketCount(int& error)
Purpose:
Retrieves the number of packets in the packet table.
Description:
This function is overloaded so that it can be called with or without returning an error value. If error is not supplied, any error value is ignored. Using this parameter allows the user to distinguish between an open packet table with 0 packets and an invalid packet table.
Parameters:
int& error (optional)
OUT: Non-negative if packet count was successfully retrieved, negative if packet table is invalid.
Returns:
Number of packets in packet table. Returns 0 if packet table contains zero packets or on error.


Name: GetDatatype
Signature:
hid_t GetDatatype ()
Purpose:
Returns the datatype of this packet table.
Description:
This function returns the identifier of the datatype used by this packet table. However, it is better to avoid using this identifier in packet table applications unless the desired functionality cannot be performed via the packet table identifier.
Returns:
Returns a valid identifier on success or H5I_INVALID_HID on error.
History:
Release Change
1.10.0 and 1.8.17     Function introduced.


Name: GetDataset
Signature:
hid_t GetDataset ()
Purpose:
Returns the dataset of this packet table.
Description:
This function returns the identifier of the dataset of this packet table. However, it is better to avoid using this identifier in packet table applications unless the desired functionality cannot be performed via the packet table identifier.
Returns:
Returns a valid identifier on success or H5I_INVALID_HID on error.
History:
Release Change
1.10.0 and 1.8.17     Function introduced.


Name: GetTableId
Signature:
hid_t GetTableId ()
Purpose:
Returns the identifier of the packet table.
Description:
This function returns the packet table identifier. However, the identifier is usually not needed by applications.
Returns:
Returns a valid identifier on success or H5I_INVALID_HID if the packet table is not valid.
History:
Release Change
1.10.0 and 1.8.17     Function introduced.


Name: FreeBuff
Signature:
FreeBuff(size_t numStructs, hvl_t * buffer)
Purpose:
Frees the buffer created when accessing data in a variable-length packet table.
Description:
Takes the number of hvl_t structs to be freed and a pointer to their location in memory.
Parameters:
size_t numStructs
IN: Number of structs to be freed.
hvl_t *buffer
IN: Pointer to location.
Returns:
Returns SUCCEED on success and FAIL on error.
History:
Release Change
1.10.0 and 1.8.17     Function introduced in this release.




FL_Packet_Table:
Name: “Create” Constructor
Signature:
FL_PacketTable(hid_t fileID, const char* ptname, hid_t dtypeID, hsize_t chunkSize)
Purpose:
Creates a new packet table for storing fixed-length or variable-length packets.
Description:
This constructor creates and opens a packet table, named ptname, in the file specified by fileID. Packets will be of the datatype specified by dtypeID. The packet table uses HDF5 chunked storage to allow it to grow. The chunk size can be specified by chunkSize. The chunk size affects performance, so it should be determined with care when performance is important.
Parameters:
hid_t fileID
IN: Identifier of the file or group to create the table within.
const char * ptname
IN: The name of the packet table to create.
hid_t dtypeID
IN: The datatype of a packet.
hsize_t chunkSize
IN: Desired chunk size; defaults to 0.
History:
Release Change
1.10.0 Function revised.


Name: “Create” Constructor (deprecated in 1.10.0 and in 1.8.17)
Signature:
FL_PacketTable(hid_t fileID, const char* ptname, hid_t dtypeID, hsize_t chunkSize, int compression)
Purpose:
Creates a new packet table for storing fixed-length packets.
Description:
This constructor has been deprecated in favor of the “Create” Constructor above, which provides flexibility in the compression method.

This constructor creates and opens a packet table in the file specified by fileID named ptname. Packets will be of the datatype specified by dtypeID. The packet can be specified to contain data with deflate compression using the parameter compression.

Parameters:
hid_t fileID
IN: Identifier of the file or group to create the table within.
const char * ptname
IN: The name of the packet table to create.
hid_t dtypeID
IN: The datatype of a packet.
hsize_t chunkSize
IN: The packet table uses HDF5 chunked storage to allow it to grow. This value allows the user to set the size of a chunk. The chunk size affects performance.
int compression
IN: Desired compression level: 0 (zero) through 9, or -1 for no compression.
History:
Release Change
1.10.0 and 1.8.17     Function revised and deprecated.


Name: “Open” Constructor
Signature:
FL_PacketTable(hid_t fileID, const char* ptname)
FL_PacketTable(hid_t fileID, char* ptname) (deprecated)
Purpose:
Opens a fixed-length packet table.
Description:
This constructor opens an existing packet table named ptname in the location fileID. This packet table can be either fixed-length or variable-length.
Parameters:
hid_t fileID
IN: Identifier of the file or group containing the packet table.
const char * ptname
IN: The name of the packet table to open.
History:
Release Change
1.10.0 and 1.8.17     Function arguments were changed.


Name: AppendPacket / AppendPackets
Signatures:
int AppendPacket(void * data)
int AppendPackets(size_t numPackets, void *data)
Purpose:
Appends packets to the packet table.
Description:
These functions write packets to the end of the packet table.
Parameters:
size_t numPackets
IN: Number of packets to add.
void * data:
IN: Data to write. Must be a buffer of packets of the packet table’s datatype.
Returns:
Returns SUCCEED on success and FAIL on error.
History:
Release Change
1.10.0 and 1.8.17     Function changed: function now works with fixed-length and variable-length packets.


Name: GetPacket / GetPackets
Signatures:
int GetPacket(hsize_t index, void * data)
int GetPackets(hsize_t startIndex, hsize_t endIndex, void * data)
Purpose:
Reads packets from the packet table.
Description:
This function fills a buffer, data, with fixed-length packets from the packet table. The one-argument function can be called to retrieve a single packet at the given index, or the two-argument function can be used to read a range of packets (zero-indexed, inclusive).
Parameters:
hsize_t index (single packet)
IN: Index of the single packet to be read.
hsize_t startIndex (multiple packets)
IN: Index at which to start reading packets.
hsize_t endIndex (multiple packets)
IN: Index at which to stop reading packets.
void * data
OUT: Buffer for packets being retrieved.
Returns:
Returns SUCCEED on success and FAIL on error.


Name: GetNextPacket / Get Next Packets
Signatures:
int GetNextPacket(void * data)
int GetNextPackets(size_t numPackets, void * data)
Purpose:
Iterates through packets from the packet table.
Description:
This function reads packets starting from the current index in the packet table and updates the index. It can be used with the ResetIndex and SetIndex functions to iterate through the packet table. GetNextPacket reads a single packet, and GetNextPackets reads numPackets packets.
Parameters:
size_t numPackets (optional)
IN: The number of packets that will be read.
void * data
OUT: Buffer to hold packets that were read.
Returns:
Returns SUCCEED on success and FAIL on error.


HDF5 documents and links 
Introduction to HDF5 
HDF5 User’s Guide 
Other High-level API documents
In the HDF5 Reference Manual  
H5DS   H5IM   H5LT   H5PT   H5TB   Optimized 
H5   H5A   H5D   H5E   H5F   H5G   H5I  
H5L   H5O   H5P   H5R   H5S   H5T   H5Z  
Tools   Datatypes   Fortran  

The HDF Group Help Desk:
Describes HDF5 Release 1.10.0
  Copyright by The HDF Group
and the Board of Trustees of the University of Illinois