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H5O_GET_INFO2

Retrieves the metadata for an object specified by an identifier

Procedure:

H5O_GET_INFO2(object_id, object_info, fields)

Signature:

herr_t H5Oget_info2( hid_t object_id, H5O_info_t *object_info, unsigned int fields)

SUBROUTINE h5oget_info_f(object_id, object_info, hdferr)

    USE, INTRINSIC :: ISO_C_BINDING
    IMPLICIT NONE
    INTEGER(HID_T)  , INTENT(IN)            :: object_id
    TYPE(h5o_info_t), INTENT(OUT), TARGET   :: object_info
    INTEGER         , INTENT(OUT)           :: hdferr

Related Fortran2003 Derived Type: h5o_info_t

  TYPE, BIND(C) :: space_t
     INTEGER(hsize_t) :: total ! Total space for storing object header in file
     INTEGER(hsize_t) :: meta  ! Space within header for object header metadata 
                               ! information
     INTEGER(hsize_t) :: mesg  ! Space within header for actual message 
                               ! information
     INTEGER(hsize_t) :: free  ! Free space within object header
  END TYPE space_t

  TYPE, BIND(C) :: mesg_t
     INTEGER(c_int64_t) :: present ! Flags to indicate presence of message type 
                                   ! in header 
     INTEGER(c_int64_t) :: shared  ! Flags to indicate message type is shared 
                                   ! in header
  END TYPE mesg_t
  
  TYPE, BIND(C) :: hdr_t
     INTEGER :: version ! Version number of header format in file
     INTEGER :: nmesgs  ! Number of object header messages
     INTEGER :: nchunks ! Number of object header chunks
     INTEGER :: flags   ! Object header status flags
     TYPE(space_t)  :: space   
     TYPE(mesg_t)   :: mesg
  END TYPE hdr_t

  ! Extra metadata storage for obj & attributes
  TYPE, BIND(C) :: H5_ih_info_t
     INTEGER(hsize_t) :: index_size ! btree and/or list
     INTEGER(hsize_t) :: heap_size
  END TYPE H5_ih_info_t

  TYPE, BIND(C) :: meta_size_t
     TYPE(H5_ih_info_t) :: obj  ! v1/v2 B-tree & local/fractal heap for 
                                ! groups, B-tree for chunked datasets
     TYPE(H5_ih_info_t) :: attr ! v2 B-tree & heap for attributes
  ENDTYPE meta_size_t
  
  TYPE, BIND(C) :: h5o_info_t
     INTEGER(C_LONG)  :: fileno     ! File number that object is located in
     INTEGER(haddr_t) :: addr       ! Object address in file  
     INTEGER(C_INT)   :: type       ! Basic object type (group, dataset, etc.) 
     INTEGER          :: rc         ! Reference count of object

     INTEGER, DIMENSION(8) :: atime ! Access time        !    -- NOTE --
     INTEGER, DIMENSION(8) :: mtime ! Modification time  ! Returns an integer 
     INTEGER, DIMENSION(8) :: ctime ! Change time        ! array as specified 
     INTEGER, DIMENSION(8) :: btime ! Birth time         ! in Fortran intrinsic 
                                                         ! DATE_AND_TIME(VALUES)

     INTEGER(hsize_t) :: num_attrs  ! # of attributes attached to object

     TYPE(hdr_t) :: hdr

     TYPE(meta_size_t) :: meta_size
  END TYPE h5o_info_t

Parameters:
hid_t object_idIN: Identifier for object of type specified by H5O_type_t; may be a file, group, dataset, named datatype or attribute identifier
H5O_info_t *object_info    OUT: Buffer in which to return object information
unsigned int fieldsIN: Flags specifying the fields to include in object_info

Description:

H5O_GET_INFO2 specifies an object by its identifier, object_id, and retrieves the metadata describing that object in object_info, an H5O_info_t struct.

An H5O_info_t struct is defined (in H5Opublic.h) as follows :

typedef struct H5O_info_t {
    unsigned long       fileno;     /* Number of file where object is       */
                                    /*   located                            */
    haddr_t             addr;       /* Object address in file               */
    H5O_type_t          type;       /* Basic object type                    */
                                    /*   (See H5O_type_t below)             */
    unsigned            rc;         /* Reference count of object            */
    time_t              atime;      /* Access time                          */
    time_t              mtime;      /* Modification time                    */
    time_t              ctime;      /* Change time                          */
    time_t              btime;      /* Birth time                           */
    hsize_t             num_attrs;  /* # of attributes attached to object   */
    H5O_hdr_info_t      hdr         /* Object header information            */
                                    /*   (See H5O_hdr_info_t below)         */
    struct {
                                    /* Extra metadata storage for obj &     */
                                    /*   attributes                         */
        H5_ih_info_t    obj;        /* v1/v2 B-tree & local/fractal heap    */
                                    /*   for groups, B-tree for chunked     */
                                    /*   datasets.                          */
                                    /*   For internal library use only.     */
        H5_ih_info_t    attr;       /* v2 B-tree & heap for attributes.     */
                                    /*   For internal library use only.     */
    } meta_size;
} H5O_info_t;
    

Note the following about H50_info_t:

Of the four time fields (atime, mtime, ctime, and btime) only ctime has been implemented.

The atime value is the last time the object was read or written.

The mtime value is the last time the raw data in the object was changed.

The ctime value is the last time the metadata for the object was changed.

The btime value is the time the object was created.

The fields nested in the meta_size field are for internal library use only.

An H5O_type_t enum indicates the object type and is defined (in H5Opublic.h) as follows:

 

typedef enum H5O_type_t {
    H5O_TYPE_UNKNOWN = -1,      /* Unknown object type                      */
    H5O_TYPE_GROUP,             /* Object is a group                        */
    H5O_TYPE_DATASET,           /* Object is a dataset                      */
    H5O_TYPE_NAMED_DATATYPE,    /* Object is a committed (named) datatype   */
    H5O_TYPE_NTYPES             /* Number of different object types (must   */
                                /* be last!)                                */
} H5O_type_t;
    

Note that object_id refers only to the types specified by H5O_type_t.

An H5O_hdr_info_t struct holds object header metadata and is defined (in H5Opublic.h) as follows:

typedef struct H5O_hdr_info_t {
    unsigned version;           /* Version number of header format in file  */
    unsigned nmesgs;            /* Number of object header messages         */
    unsigned nchunks;           /* Number of object header chunks           */
    unsigned flags;             /* Object header status flags               */
    struct {
        hsize_t total;          /* Total space for storing object header in */ 
                                /*   file                                   */
        hsize_t meta;           /* Space within header for object header    */
                                /*   metadata information                   */
        hsize_t mesg;           /* Space within header for actual message   */
                                /*   information                            */
        hsize_t free;           /* Free space within object header          */
    } space;
    struct {
        uint64_t present;       /* Flags to indicate presence of message    */
                                /*   type in header                         */
        uint64_t shared;        /* Flags to indicate message type is        */
                                /*   shared in header                       */
    } mesg;
} H5O_hdr_info_t;
    

Valid values for the version field are H5O_VERSION_1 and H5O_VERSION_2. Version 2 of the object header is smaller and more efficient than version 1.

The fields parameter contains flags to determine which fields will be filled in in the H5O_info_t struct returned in object_info. These flags are defined in the H5Opublic.h file:

FlagPurpose
H5O_INFO_BASICFill in the fileno, addr, type, and rc fields
H5O_INFO_TIMEFill in the atime, mtime, ctime, and btime fields
H5O_INFO_NUM_ATTRSFill in the num_attrs field
H5O_INFO_HDRFill in the hdr field
H5O_INFO_META_SIZEFill in the meta_size field
H5O_INFO_ALLH5O_INFO_BASIC | H5O_INFO_TIME | H5O_INFO_NUM_ATTRS | H5O_INFO_HDR | H5O_INFO_META_SIZE

 

Please be aware that the information held by H5O_hdr_info_t may only be useful to developers with extensive HDF5 experience.

Note:

If you are iterating through a lot of different objects to retrieve information via the H5O_GET_INFO family of routines, you may see memory building up. This can be due to memory allocation for metadata such as  object headers and messages when the iterated objects are put into the metadata cache.

If the memory buildup is not desirable, you can configure a smaller cache via H5F_SET_MDC_CONFIG or set the file access property list via H5P_SET_MDC_CONFIG. A smaller sized cache will force metadata entries to be evicted from the cache, thus freeing the memory associated with the entries.

Returns:

Returns a non-negative value if successful; otherwise returns a negative value.

Example:

Coming Soon!

History:
Release    Change
1.10.3C function introduced in this release.

--- Last Modified: August 16, 2018 | 11:16 AM