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HDF5
1.14.4.3
API Reference
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HDF5
1.14.4.3
API Reference
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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.
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. | |
Appends packets to the end of a packet table.
| [in] | table_id | Identifier of packet table to which packets should be appended |
| [in] | nrecords | Number of packets to be appended |
| [in] | data | Buffer holding data to write |
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.
Closes an open packet table.
| [in] | table_id | Identifier of packet table to be closed |
The H5PTclose() ends access to a packet table specified by table_id.
| 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.
| [in] | loc_id | Location identifier. The identifier may be that of a file or group. |
| [in] | dset_name | The name of the packet table to create |
| [in] | dtype_id | The datatype of the packet |
| [in] | chunk_size | The size in number of table entries per chunk |
| [in] | plist_id | Identifier of the property list. Can be used to specify the compression of the packet table. |
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.
| 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.
| [in] | loc_id | Location identifier. The identifier may be that of a file or group. |
| [in] | dset_name | The name of the dataset to create |
| [in] | dtype_id | The datatype of a packet. |
| [in] | chunk_size | The size in number of table entries per chunk. |
| [in] | compression | The compression level; a value of 0 through 9. |
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.
Resets a packet table's index to the first packet.
| [in] | table_id | Identifier of packet table whose index should be initialized. |
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.
Releases memory allocated in the process of reading variable-length packets.
| [in] | table_id | Packet table whose memory should be freed. |
| [in] | bufflen | Size of buff |
| [in] | buff | Buffer that was used to read in variable-length packets |
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.
Returns the backend dataset of this packet table.
| [in] | table_id | Identifier of the packet table |
The H5PTget_dataset() returns the identifier of the dataset storing the packet table table_id. This dataset identifier will be closed by H5PTclose().
Gets the current record index for a packet table.
| [in] | table_id | Table identifier |
| [out] | pt_index | Current record index |
The H5PTget_index() returns the current record index pt_index for the table identified by table_id.
Reads packets from a packet table starting at the current index.
| [in] | table_id | Identifier of packet table to read from |
| [in] | nrecords | Number of packets to be read |
| [out] | data | Buffer into which to read data |
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().
Returns the number of packets in a packet table.
| [in] | table_id | Identifier of packet table to query |
| [out] | nrecords | Number of packets in packet table |
The H5PTget_num_packets() returns by reference the number of packets in a packet table specified by table_id.
Returns the backend datatype of this packet table.
| [in] | table_id | Identifier of the packet table |
The H5PTget_type() returns the identifier of the datatype used by the packet table table_id. This datatype identifier will be closed by H5PTclose().
Determines whether an identifier points to a packet table.
| [in] | table_id | Identifier to query |
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.
Determines whether a packet table contains variable-length or fixed-length packets.
| [in] | table_id | Packet table to query |
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.
Opens an existing packet table.
| [in] | loc_id | Location identifier. The identifier may be that of a file or group. |
| [in] | dset_name | The name of the packet table to open |
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().
Reads a number of packets from a packet table.
| [in] | table_id | Identifier of packet table to read from |
| [in] | start | Packet to start reading from |
| [in] | nrecords | Number of packets to be read |
| [out] | data | Buffer into which to read data. |
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().
Sets a packet table's index.
| [in] | table_id | Identifier of packet table whose index is to be set |
| [in] | pt_index | The packet to which the index should point |
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).
1.9.7