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HDF5 1.14.5
API Reference
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HDF5 Packet Table APIs (H5PT)

Detailed Description

Creating and manipulating HDF5 datasets to support append- and read-only operations on table data (H5PT)

The HDF5 Packet Table API is designed to allow records to be appended to and read from a table. Packet Table datasets are chunked, allowing them to grow as needed.

The Packet Table API, with the H5PT prefix, is not to be confused with the H5TB Table API (H5TB prefix). The H5TB APIs are stateless (H5TB Tables do not need to be opened or closed) but H5PT Packet Tables require less performance overhead. Also, H5TB Tables support insertions and deletions, while H5PT Packet Tables support only append operations. H5TB functions should not be called on tables created with the H5PT API, or vice versa.

Packet Tables are datasets in an HDF5 file, so while their contents should not be changed outside of the H5PT API calls, the datatypes of Packet Tables can be queried using H5Dget_type. Packet Tables can also be given attributes using the normal HDF5 APIs.

Note
Programming hints:
The following line includes the HDF5 Packet Table package, H5PT, in C applications:
#include "hdf5_hl.h"
Without this include, an application will not have access to these functions.

Functions

H5_HLDLL hid_t H5PTcreate (hid_t loc_id, const char *dset_name, hid_t dtype_id, hsize_t chunk_size, hid_t plist_id)
 Creates a packet table to store fixed-length or variable-length packets.
 
H5_HLDLL hid_t H5PTopen (hid_t loc_id, const char *dset_name)
 Opens an existing packet table.
 
H5_HLDLL herr_t H5PTclose (hid_t table_id)
 Closes an open packet table.
 
H5_HLDLL hid_t H5PTcreate_fl (hid_t loc_id, const char *dset_name, hid_t dtype_id, hsize_t chunk_size, int compression)
 Creates a packet table to store fixed-length packets.
 
H5_HLDLL herr_t H5PTappend (hid_t table_id, size_t nrecords, const void *data)
 Appends packets to the end of a packet table.
 
H5_HLDLL herr_t H5PTget_next (hid_t table_id, size_t nrecords, void *data)
 Reads packets from a packet table starting at the current index.
 
H5_HLDLL herr_t H5PTread_packets (hid_t table_id, hsize_t start, size_t nrecords, void *data)
 Reads a number of packets from a packet table.
 
H5_HLDLL herr_t H5PTget_num_packets (hid_t table_id, hsize_t *nrecords)
 Returns the number of packets in a packet table.
 
H5_HLDLL herr_t H5PTis_valid (hid_t table_id)
 Determines whether an identifier points to a packet table.
 
H5_HLDLL herr_t H5PTis_varlen (hid_t table_id)
 Determines whether a packet table contains variable-length or fixed-length packets.
 
H5_HLDLL hid_t H5PTget_dataset (hid_t table_id)
 Returns the backend dataset of this packet table.
 
H5_HLDLL hid_t H5PTget_type (hid_t table_id)
 Returns the backend datatype of this packet table.
 
H5_HLDLL herr_t H5PTcreate_index (hid_t table_id)
 Resets a packet table's index to the first packet.
 
H5_HLDLL herr_t H5PTset_index (hid_t table_id, hsize_t pt_index)
 Sets a packet table's index.
 
H5_HLDLL herr_t H5PTget_index (hid_t table_id, hsize_t *pt_index)
 Gets the current record index for a packet table.
 
H5_HLDLL herr_t H5PTfree_vlen_buff (hid_t table_id, size_t bufflen, void *buff)
 Releases memory allocated in the process of reading variable-length packets.
 

Function Documentation

◆ H5PTappend()

H5_HLDLL herr_t H5PTappend ( hid_t  table_id,
size_t  nrecords,
const void *  data 
)

Appends packets to the end of a packet table.


Parameters
[in]table_idIdentifier of packet table to which packets should be appended
[in]nrecordsNumber of packets to be appended
[in]dataBuffer holding data to write
Returns
Returns a non-negative value if successful; otherwise, returns a negative value.

The H5PTappend() writes nrecords packets to the end of a packet table specified by table_id. data is a buffer containing the data to be written. For a packet table holding fixed-length packets, this data should be in the packet table's datatype. For a variable-length packet table, the data should be in the form of hvl_t structs.

◆ H5PTclose()

H5_HLDLL herr_t H5PTclose ( hid_t  table_id)

Closes an open packet table.


Parameters
[in]table_idIdentifier of packet table to be closed
Returns
Returns a non-negative value if successful; otherwise, returns a negative value.

The H5PTclose() ends access to a packet table specified by table_id.

◆ H5PTcreate()

H5_HLDLL hid_t H5PTcreate ( hid_t  loc_id,
const char *  dset_name,
hid_t  dtype_id,
hsize_t  chunk_size,
hid_t  plist_id 
)

Creates a packet table to store fixed-length or variable-length packets.


Parameters
[in]loc_idLocation identifier. The identifier may be that of a file or group.
[in]dset_nameThe name of the packet table to create
[in]dtype_idThe datatype of the packet
[in]chunk_sizeThe size in number of table entries per chunk
[in]plist_idIdentifier of the property list. Can be used to specify the compression of the packet table.
Returns
Returns an identifier for the new packet table or H5I_INVALID_HID on error.

The H5PTcreate() creates and opens a packet table named dset_name attached to the object specified by the identifier loc_id. The created packet table should be closed with H5PTclose(), eventually.

The datatype, dtype_id, may specify any datatype, including variable-length data. If dtype_id specifies a compound datatype, one or more fields in that compound type may be variable-length.

chunk_size is the size in number of table entries per chunk. Packet table datasets use HDF5 chunked storage to allow them to grow. This value allows the user to set the size of a chunk. The chunk size affects performance.

Since
1.10.0 and 1.8.17

◆ H5PTcreate_fl()

H5_HLDLL hid_t H5PTcreate_fl ( hid_t  loc_id,
const char *  dset_name,
hid_t  dtype_id,
hsize_t  chunk_size,
int  compression 
)

Creates a packet table to store fixed-length packets.


Parameters
[in]loc_idLocation identifier. The identifier may be that of a file or group.
[in]dset_nameThe name of the dataset to create
[in]dtype_idThe datatype of a packet.
[in]chunk_sizeThe size in number of table entries per chunk.
[in]compressionThe compression level; a value of 0 through 9.
Returns
Returns an identifier for the packet table or H5I_INVALID_HID on error.
Deprecated:
This function was deprecated in favor of the function H5PTcreate().

The H5PTcreate_fl() creates and opens a packet table named dset_name attached to the object specified by the identifier loc_id. It should be closed with H5PTclose().

The datatype, dtype_id, may specify any datatype, including variable-length data. If dtype_id specifies a compound datatype, one or more fields in that compound type may be variable-length.

chunk_size is the size in number of table entries per chunk. Packet table datasets use HDF5 chunked storage to allow them to grow. This value allows the user to set the size of a chunk. The chunk size affects performance.

compression is the compression level, a value of 0 through 9. Level 0 is faster but offers the least compression; level 9 is slower but offers maximum compression. A setting of -1 indicates that no compression is desired.

◆ H5PTcreate_index()

H5_HLDLL herr_t H5PTcreate_index ( hid_t  table_id)

Resets a packet table's index to the first packet.


Parameters
[in]table_idIdentifier of packet table whose index should be initialized.
Returns
Returns a non-negative value if successful; otherwise, returns a negative value.

Each packet table keeps an index of the "current" packet so that get_next can iterate through the packets in order. H5PTcreate_index() initializes a packet table's index, and should be called before using get_next. The index must be initialized every time a packet table is created or opened; this information is lost when the packet table is closed.

◆ H5PTfree_vlen_buff()

H5_HLDLL herr_t H5PTfree_vlen_buff ( hid_t  table_id,
size_t  bufflen,
void *  buff 
)

Releases memory allocated in the process of reading variable-length packets.


Parameters
[in]table_idPacket table whose memory should be freed.
[in]bufflenSize of buff
[in]buffBuffer that was used to read in variable-length packets
Returns
Returns a non-negative value if successful; otherwise, returns a negative value.

When variable-length packets are read, memory is automatically allocated to hold them, and must be freed. H5PTfree_vlen_buff() frees this memory, and should be called whenever packets are read from a variable-length packet table.

Version
1.10.0 and 1.8.17 Function re-introduced. Function had been removed in 1.8.3.

◆ H5PTget_dataset()

H5_HLDLL hid_t H5PTget_dataset ( hid_t  table_id)

Returns the backend dataset of this packet table.


Parameters
[in]table_idIdentifier of the packet table
Returns
Returns a dataset identifier or H5I_INVALID_HID on error.

The H5PTget_dataset() returns the identifier of the dataset storing the packet table table_id. This dataset identifier will be closed by H5PTclose().

Since
1.10.0 and 1.8.17

◆ H5PTget_index()

H5_HLDLL herr_t H5PTget_index ( hid_t  table_id,
hsize_t pt_index 
)

Gets the current record index for a packet table.


Parameters
[in]table_idTable identifier
[out]pt_indexCurrent record index
Returns
Returns a non-negative value if successful; otherwise, returns a negative value.

The H5PTget_index() returns the current record index pt_index for the table identified by table_id.

Since
1.8.0

◆ H5PTget_next()

H5_HLDLL herr_t H5PTget_next ( hid_t  table_id,
size_t  nrecords,
void *  data 
)

Reads packets from a packet table starting at the current index.


Parameters
[in]table_idIdentifier of packet table to read from
[in]nrecordsNumber of packets to be read
[out]dataBuffer into which to read data
Returns
Returns a non-negative value if successful; otherwise, returns a negative value.

The H5PTget_next() reads nrecords packets starting with the "current index" from a packet table specified by table_id. The packet table's index is set and reset with H5PTset_index() and H5PTcreate_index(). data is a buffer into which the data should be read.

For a packet table holding variable-length records, the data returned in the buffer will be in form of a hvl_t struct containing the length of the data and a pointer to it in memory. The memory used by this data must be freed using H5PTfree_vlen_buff().

◆ H5PTget_num_packets()

H5_HLDLL herr_t H5PTget_num_packets ( hid_t  table_id,
hsize_t nrecords 
)

Returns the number of packets in a packet table.


Parameters
[in]table_idIdentifier of packet table to query
[out]nrecordsNumber of packets in packet table
Returns
Returns a non-negative value if successful; otherwise, returns a negative value.

The H5PTget_num_packets() returns by reference the number of packets in a packet table specified by table_id.

◆ H5PTget_type()

H5_HLDLL hid_t H5PTget_type ( hid_t  table_id)

Returns the backend datatype of this packet table.


Parameters
[in]table_idIdentifier of the packet table
Returns
Returns a datatype identifier or H5I_INVALID_HID on error.

The H5PTget_type() returns the identifier of the datatype used by the packet table table_id. This datatype identifier will be closed by H5PTclose().

Since
1.10.0 and 1.8.17

◆ H5PTis_valid()

H5_HLDLL herr_t H5PTis_valid ( hid_t  table_id)

Determines whether an identifier points to a packet table.


Parameters
[in]table_idIdentifier to query
Returns
Returns a non-negative value if table_id is a valid packet table, otherwise returns a negative value.

The H5PTis_valid() returns a non-negative value if table_id corresponds to an open packet table, and returns a negative value otherwise.

◆ H5PTis_varlen()

H5_HLDLL herr_t H5PTis_varlen ( hid_t  table_id)

Determines whether a packet table contains variable-length or fixed-length packets.


Parameters
[in]table_idPacket table to query
Returns
Returns 1 for a variable-length packet table, 0 for fixed-length, or a negative value on error.

The H5PTis_varlen() returns 1 (TRUE) if table_id is a packet table containing variable-length records. It returns 0 (FALSE) if table_id is a packet table containing fixed-length records. If table_id is not a packet table, a negative value is returned.

Version
1.10.0 and 1.8.17 Function re-introduced. Function had been removed in 1.8.3.

◆ H5PTopen()

H5_HLDLL hid_t H5PTopen ( hid_t  loc_id,
const char *  dset_name 
)

Opens an existing packet table.


Parameters
[in]loc_idLocation identifier. The identifier may be that of a file or group.
[in]dset_nameThe name of the packet table to open
Returns
Returns an identifier for the packet table or H5I_INVALID_HID on error.

H5PTopen() opens an existing packet table in the file or group specified by loc_id. dset_name is the name of the packet table and is used to identify it in the file. This function is used to open both fixed-length packet tables and variable-length packet tables. The packet table should later be closed with H5PTclose().

◆ H5PTread_packets()

H5_HLDLL herr_t H5PTread_packets ( hid_t  table_id,
hsize_t  start,
size_t  nrecords,
void *  data 
)

Reads a number of packets from a packet table.


Parameters
[in]table_idIdentifier of packet table to read from
[in]startPacket to start reading from
[in]nrecordsNumber of packets to be read
[out]dataBuffer into which to read data.
Returns
Returns a non-negative value if successful; otherwise, returns a negative value.

The H5PTread_packets() reads nrecords packets starting at packet number start from a packet table specified by table_id. data is a buffer into which the data should be read.

For a packet table holding variable-length records, the data returned in the buffer will be in form of hvl_t structs, each containing the length of the data and a pointer to it in memory. The memory used by this data must be freed using H5PTfree_vlen_buff().

◆ H5PTset_index()

H5_HLDLL herr_t H5PTset_index ( hid_t  table_id,
hsize_t  pt_index 
)

Sets a packet table's index.


Parameters
[in]table_idIdentifier of packet table whose index is to be set
[in]pt_indexThe packet to which the index should point
Returns
Returns a non-negative value if successful; otherwise, returns a negative value.

Each packet table keeps an index of the "current" packet so that get_next can iterate through the packets in order. H5PTset_index() sets this index to point to a user-specified packet (the packets are zero-indexed).