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HDF5 documents and links Introduction to HDF5 HDF5 User Guide |
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HDF5 Reference Manual
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The C Interfaces:
A group associates names with objects and provides a mechanism for mapping a name to an object. Since all objects appear in at least one group (with the possible exception of the root object) and since objects can have names in more than one group, the set of all objects in an HDF5 file is a directed graph. The internal nodes (nodes with out-degree greater than zero) must be groups while the leaf nodes (nodes with out-degree zero) are either empty groups or objects of some other type. Exactly one object in every non-empty file is the root object. The root object always has a positive in-degree because it is pointed to by the file super block.
An object name consists of one or more components separated from one another by slashes. An absolute name begins with a slash and the object is located by looking for the first component in the root object, then looking for the second component in the first object, etc., until the entire name is traversed. A relative name does not begin with a slash and the traversal begins at the location specified by the create or access function.
H5Gclose(hid_t group_id)
H5Gclose releases resources used by a group which was
opened by H5Gcreate or H5Gopen.
After closing a group, the group_id cannot be used again.
Failure to release a group with this call will result in resource leaks.
group_id
H5Gcreate(hid_t loc_id,
const char *name,
size_t size_hint
)
H5Gcreate creates a new group with the specified
name at the specified location, loc_id.
The location is identified by a file or group identifier.
The name, name, must not already be taken by some
other object and all parent groups must already exist.
size_hint is a hint for the number of bytes to
reserve to store the names which will be eventually added to
the new group. Passing a value of zero for size_hint
is usually adequate since the library is able to dynamically
resize the name heap, but a correct hint may result in better
performance.
If a non-positive value is supplied for size_hint,
then a default size is chosen.
The return value is a group identifier for the open group.
This group identifier should be closed by calling
H5Gclose when it is no longer needed.
loc_id
name
size_hint
H5Gget_comment(hid_t loc_id,
const char *name,
size_t bufsize,
char *comment
)
H5Gget_comment retrieves the comment for the the
object name. The comment is returned in the buffer
comment.
At most bufsize characters, including a null
terminator, are copied. The result is not null terminated
if the comment is longer than the supplied buffer.
If an object does not have a comment, the empty string is returned.
loc_id
name
bufsize
comment.
comment
bufsize.
Otherwise returns a negative value.
H5Gget_linkval(hid_t loc_id,
const char *name,
size_t size,
char *value
)
H5Gget_linkval returns size
characters of the name of the object that the symbolic link name points to.
The parameter loc_id is a file or group identifier.
The parameter name must be a symbolic link pointing to
the desired object and must be defined relative to loc_id.
If size is smaller than the size of the returned object name, then
the name stored in the buffer value will not be null terminated.
This function fails if name is not a symbolic link.
The presence of a symbolic link can be tested by passing zero for
size and NULL for value.
This function should be used only after H5Gget_objinfo has been called
to verify that name is a symbolic link.
loc_id
name
size
value
to be returned.
value
value,
if successful.
Otherwise returns a negative value.
H5Gget_num_objs(hid_t loc_id,
hsize_t* num_obj)
H5Gget_num_objs returns number of objects in a group.
Group is specified by its identifier loc_id.
If a file identifier is passed in, then number of objects in the
root group is returned.
loc_id
num_obj
H5Gget_objinfo(hid_t loc_id,
const char *name,
hbool_t follow_link,
H5G_stat_t *statbuf
)
H5Gget_objinfo returns information about the
specified object through the statbuf argument.
loc_id (a file or group identifier) and
name together determine the object.
If the object is a symbolic link and follow_link is
zero (0), then the information returned is that for the link itself;
otherwise the link is followed and information is returned about
the object to which the link points.
If follow_link is non-zero but the final symbolic link
is dangling (does not point to anything), then an error is returned.
The statbuf fields are undefined for an error.
The existence of an object can be tested by calling this function
with a null statbuf.
H5Gget_objinfo fills in the following data structure:
typedef struct H5G_stat_t {
unsigned long fileno;
haddr_t objno;
unsigned nlink;
int type;
time_t mtime;
size_t linklen;
} H5G_stat_t
The fileno and objno fields contain
values which uniquely itentify an object among those
HDF5 files which are open: if both values are the same
between two objects, then the two objects are the same
(provided both files are still open).
fileno will change.
H5Fopen calls referencing the same file
actually open the same file, each will get a different
fileno.
The nlink field is the number of hard links to
the object or zero when information is being returned about a
symbolic link (symbolic links do not have hard links but
all other objects always have at least one).
The type field contains the type of the object,
one of
H5G_GROUP,
H5G_DATASET,
H5G_LINK, or
H5G_TYPE.
The mtime field contains the modification time.
If information is being returned about a symbolic link then
linklen will be the length of the link value
(the name of the pointed-to object with the null terminator);
otherwise linklen will be zero.
Other fields may be added to this structure in the future.
mtime value of 0 (zero).
loc_id
*name
follow_link
*statbuf
statbuf (if non-null) initialized.
Otherwise returns a negative value.
H5Gget_objname_by_idx(hid_t loc_id,
hsize_t idx,
char *name,
size_t* size )
H5Gget_objname_by_idx returns a name of the object
specified by the index idx in the group loc_id.
The group is specified by a group identifier loc_id.
If preferred, a file identifier may be passed in loc_id;
that file's root group will be assumed.
idx is the transient index used to iterate through
the objects in the group.
The value of idx is any nonnegative number less than
the total number of objects in the group, which is returned by the
function H5Gget_num_objs.
Note that this is a transient index; an object may have a
different index each time a group is opened.
The object name is returned in the user-specified buffer name.
If the size of the provided buffer name is
less or equal the actual object name length,
the object name is truncated to max_size - 1 characters.
Note that if the size of the object's name is unkown, a
preliminary call to H5Gget_objname_by_idx with name
set to NULL will return the length of the object's name.
A second call to H5Gget_objname_by_idx
can then be used to retrieve the actual name.
loc_id
idx
name
size
H5Gget_objtype_by_idx(hid_t loc_id,
hsize_t idx )
H5Gget_objtype_by_idx returns the type of the object
specified by the index idx in the group loc_id.
The group is specified by a group identifier loc_id.
If preferred, a file identifier may be passed in loc_id;
that file's root group will be assumed.
idx is the transient index used to iterate through
the objects in the group.
This parameter is described in more detail in the discussion of
H5Gget_objname_by_idx.
The object type is returned as the function return value:
H5G_LINK
|
0
| Object is a symbolic link. | |
H5G_GROUP
|
1
| Object is a group. | |
H5G_DATASET
|
2
| Object is a dataset. | |
H5G_TYPE
|
3
| Object is a named datatype. |
loc_id
idx
H5Giterate(hid_t loc_id,
const char *name,
int *idx,
H5G_iterate_t operator,
void *operator_data
)
H5Giterate iterates over the members of
name in the file or group specified with
loc_id.
For each object in the group, the operator_data
and some additional information, specified below, are
passed to the operator function.
The iteration begins with the idx object in the
group and the next element to be processed by the operator is
returned in idx. If idx
is NULL, then the iterator starts at the first group member;
since no stopping point is returned in this case, the iterator
cannot be restarted if one of the calls to its operator returns
non-zero.
The prototype for H5G_iterate_t is:
typedef herr_t (*H5G_iterate_t)(hid_t group_id,
const char *member_name,
void *operator_data);
group_id, the name of the current
object within the group, member_name, and the
pointer to the operator data passed in to H5Giterate,
operator_data.
The return values from an operator are:
H5Giterate assumes that the membership of the group
identified by name remains unchanged through the
iteration. If the membership changes during the iteration,
the function's behavior is undefined.
loc_id
*name
*idx
operator
*operator_data
H5Giterate.
Instead, that functionality is provided by two FORTRAN functions:
h5gn_members_f.
| Purpose: Returns the number of group members. | |
h5gget_obj_info_idx_f
| Purpose: Returns name and type of the group member identified by its index. |
H5Glink(hid_t loc_id,
H5G_link_t link_type,
const char *current_name,
const char *new_name
)
new_name
to current_name.
H5Glink creates a new name for an object that has some current
name, possibly one of many names it currently has.
If link_type is H5G_LINK_HARD, then
current_name must specify the name of an
existing object and both
names are interpreted relative to loc_id, which is
either a file identifier or a group identifier.
If link_type is H5G_LINK_SOFT, then
current_name can be anything and is interpreted at
lookup time relative to the group which contains the final
component of new_name. For instance, if
current_name is ./foo,
new_name is ./x/y/bar, and a request
is made for ./x/y/bar, then the actual object looked
up is ./x/y/./foo.
loc_id
link_type
H5G_LINK_HARD and
H5G_LINK_SOFT.
current_name
new_name
H5Glink2(
hid_t curr_loc_id, const char *current_name,
H5G_link_t link_type,
hid_t new_loc_id, const char *new_name )
new_name
to current_name.
H5Glink2 creates a new name for an object that has some current
name, possibly one of many names it currently has.
If link_type is H5G_LINK_HARD, then current_name
must specify the name of an existing object.
In this case, current_name and new_name are interpreted
relative to curr_loc_id and new_loc_id, respectively,
which are either file or group identifiers.
If link_type is H5G_LINK_SOFT, then
current_name can be anything and is interpreted at
lookup time relative to the group which contains the final
component of new_name. For instance, if
current_name is ./foo,
new_name is ./x/y/bar, and a request
is made for ./x/y/bar, then the actual object looked
up is ./x/y/./foo.
curr_loc_id
current_name
link_type
H5G_LINK_HARD and
H5G_LINK_SOFT.
new_loc_id
new_name
H5Gmove(hid_t loc_id,
const char *src_name,
const char *dst_name
)
H5Gmove renames an object within an HDF5 file.
The original name, src_name, is unlinked from the
group graph and the new name, dst_name, is inserted
as an atomic operation. Both names are interpreted relative
to loc_id, which is either a file or a group
identifier.
H5Gmove.
See The Group Interface
in the HDF5 User's Guide.
loc_id
*src_name
*dst_name
H5Gmove2( hid_t src_loc_id,
const char *src_name, hid_t dst_loc_id,
const char *dst_name )
H5Gmove2 renames an object within an HDF5 file. The original
name, src_name, is unlinked from the group graph and the new
name, dst_name, is inserted as an atomic operation.
src_name and dst_name are interpreted relative to
src_name and dst_name, respectively,
which are either file or group identifiers.
H5Gmove. See The
Group Interface in the HDF5 User's Guide.
src_loc_id
*src_name
dst_loc_id
*dst_name
H5Gopen(hid_t loc_id,
const char *name
)
H5Gopen opens an existing group with the specified
name at the specified location, loc_id.
The location is identified by a file or group identifier
H5Gopen returns a group identifier for the group
that was opened. This group identifier should be released by
calling H5Gclose when it is no longer needed.
loc_id
name
H5Gset_comment(hid_t loc_id,
const char *name,
const char *comment
)
H5Gset_comment sets the comment for the the
object name to comment.
Any previously existing comment is overwritten.
If comment is the empty string or a
null pointer, the comment message is removed from the object.
Comments should be relatively short, null-terminated, ASCII strings.
Comments can be attached to any object that has an object header, e.g., data sets, groups, named data types, and data spaces, but not symbolic links.
loc_id
name
comment
H5Gunlink(hid_t loc_id,
const char *name
)
H5Gunlink removes the object specified by
name from the group graph and decrements the
link count for the object to which name points.
This action eliminates any association between name
and the object to which name pointed.
Object headers keep track of how many hard links refer to an object; when the link count reaches zero, the object can be removed from the file. Objects which are open are not removed until all identifiers to the object are closed.
If the link count reaches zero, all file space associated with the object will be released, i.e., identified in memory as freespace. If the any object identifier is open for the object, the space will not be released until after the object identifier is closed.
Note that space identified as freespace is available for re-use only as long as the file remains open; once a file has been closed, the HDF5 library loses track of freespace. See “Freespace Management” in the HDF5 User's Guide for further details.
H5Gunlink.
See The Group Interface
in the HDF5 User's Guide.
loc_id
name
|
HDF5 documents and links Introduction to HDF5 HDF5 User Guide |
And in this document, the
HDF5 Reference Manual
H5 H5A H5D H5E H5F H5G H5I H5P H5R H5S H5T H5Z Tools Datatypes |