H5PT: HDF5 Packet Table
C++ Wrappers

• PacketTable - functions shared by all packet tables
• FL_PacketTable - a packet table storing fixed-length and variable-length packets

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.

Name: “Create” Constructor

Signature:

FL_PacketTable(hid_t fileID, const char* ptname, hid_t dtypeID, hsize_t chunkSize, hid_t plistID)

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. Compression can be set via the dataset creation property list, specified by plistID.

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.

hid_t plistID

IN: Identifier of the creation property list; defaults to H5P_DEFAULT.

History:

Release	Change
1.10.1 and 1.8.17	Function revised.

Name: “Create” Constructor (deprecated)

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.

The HDF Group Help Desk: Describes HDF5 Release 1.8.20, November 2017.

Copyright by The HDF Group and the Board of Trustees of the University of Illinois