/** \page UsingIdentifiers Using Identifiers
 *
 * Navigate back: \ref index "Main" / \ref UG / \ref AR_UG
 * <hr>
 *
 * \section sec_using_identifiers Using Identifiers
 *
 * The purpose of this topic is to describe how identifiers behave and how they should be treated by application programs.
 *
 * When an application program uses the HDF5 library to create or open an item, a unique identifier is
 * returned. The items that return a unique identifier when they are created or opened include the following:
 * \li dataset
 * \li group
 * \li datatype
 * \li dataspace
 * \li file
 * \li attribute
 * \li property list
 * \li referenced object
 * \li error stack
 * \li error message
 *
 * An application may open one of the items listed above more than once at the same time. For example, an
 * application might open a group twice, receiving two identifiers. Information from one dataset in the
 * group could be handled through one identifier, and the information from another dataset in the group
 * could be handled by a different identifier.
 *
 * An application program should track every identifier it receives as a result of creating or opening one of
 * the items listed above. In order for an application to close properly, it must release every identifier it
 * has opened. If an application opened a group twice for example, it would need to issue two #H5Gclose
 * commands, one for each identifier. Not releasing identifiers causes resource leaks. Until an identifier
 * is released, the item associated with the identifier is still open.
 *
 * The library considers a file open until all of the identifiers associated with the file and with the file’s
 * various items have been released. The identifiers associated with these open items must be released separately.
 * This means that an application can close a file and still work with one or more portions of the file. Suppose
 * an application opened a file, a group within the file, and two datasets within the group. If the application
 * closed the file with #H5Fclose, then the file would be considered closed to the application, but the group
 * and two datasets would still be open.
 *
 * There are several exceptions to the above file closing rule. One is when the #H5close function is used
 * instead of #H5Fclose. #H5close causes a general shut down of the library: all data is written to disk,
 * all identifiers are closed, and all memory used by the library is cleaned up. Another exception occurs on
 * parallel processing systems. Suppose on a parallel system an application has opened a file, a group in the
 * file, and two datasets in the group. If the application uses the #H5Fclose function to close the file, the
 * call will fail with an error. The open group and datasets must be closed before the file can be closed.
 * A third exception is when the file access property list includes the property #H5F_CLOSE_STRONG. This
 * property causes the closing of all of the file’s open items when the file is closed with #H5Fclose. For
 * more information about #H5close, #H5Fclose, and #H5Pset_fclose_degree, see the \ref RM.
 *
 * The reference manual entries for functions that return identifiers describe what might be returned as
 * follows:
 * \b Returns:
 *      Returns an identifier if successful; otherwise returns a negative value.
 *
 * In other words, a successful operation will return a non-negative identifier which will never be 0
 * (zero) and will always be a positive value.
 *
 * \subsection subsec_using_identifiers_func Functions that Return Identifiers
 *
 * Some of the functions that return identifiers are listed below.
 *
 * \li #H5Acreate
 * \li #H5Acreate_by_name
 * \li #H5Aget_type
 * \li #H5Aopen
 * \li #H5Aopen_by_idx
 * \li #H5Aopen_by_name
 * \li #H5Dcreate
 * \li #H5Dcreate_anon
 * \li #H5Dget_access_plist
 * \li #H5Dget_create_plist
 * \li #H5Dget_space
 * \li #H5Dget_type
 * \li #H5Dopen
 * \li #H5Ecreate_msg
 * \li #H5Ecreate_stack
 * \li #H5Fcreate
 * \li #H5Fopen
 * \li #H5Freopen
 * \li #H5Gcreate
 * \li #H5Gcreate_anon
 * \li #H5Gopen
 * \li #H5Oopen
 * \li #H5Oopen_by_addr
 * \li #H5Oopen_by_idx
 * \li #H5Pcreate
 * \li #H5Pget_virtual_srcspace
 * \li #H5Pget_virtual_vspace
 * \li #H5Rdereference
 * \li #H5Rget_region
 * \li #H5Screate
 * \li #H5Screate_simple
 * \li #H5Tcopy
 * \li #H5Tcreate
 * \li #H5Tdecode
 * \li #H5Tget_member_type
 * \li #H5Tget_super
 * \li #H5Topen
 *
 * <hr>
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*/