Determines whether a link resolves to an actual object
Procedure:
H5O_EXISTS_BY_NAME(loc_id, name, lapl_id)
Signature:
htri_t H5Oexists_by_name( hid_t loc_id, const char * name, hid_t lapl_id )
SUBROUTINE h5oexists_by_name_f(loc_id, name, link_exists, &
hdferr, lapl_id)
IMPLICIT NONE
INTEGER(HID_T) , INTENT(IN) :: loc_id
CHARACTER(LEN=*), INTENT(IN) :: name
LOGICAL , INTENT(OUT) :: link_exists
INTEGER , INTENT(OUT) :: hdferr
INTEGER(HID_T) , INTENT(IN), OPTIONAL :: lapl_id
Parameters:
hid_t loc_id | IN: Location Identifier to query; may be a file, group, dataset, named datatype or attribute identifier |
const char *name | IN: The name of the link to check |
hid_t lapl_id | IN: Link access property list identifier |
Description:
H5O_EXISTS_BY_NAME allows an application to determine whether the link name
in the group or file specified with loc_id
resolves to an HDF5 object to open or if the link dangles. The link may be of any type, but hard links will always resolve to objects and do not need to be verified.
Note that H5O_EXISTS_BY_NAME verifies only that the target object exists. If name
includes either a relative path or an absolute path to the target link, intermediate steps along the path must be verified before the existence of the target link can be safely checked. If the path is not verified and an intermediate element of the path does not exist, H5O_EXISTS_BY_NAME will fail. The example in the next paragraph illustrates one step-by-step method for verifying the existence of a link with a relative or absolute path.
Example: Use the following steps to verify the existence of the link datasetD
in the group group1/group2/softlink_to_group3/
, where group1
is a member of the group specified by loc_id
:
- First use H5L_EXISTS to verify that a link named
group1
exists. - If
group1
exists, use H5O_EXISTS_BY_NAME to verify that the link group1
resolves to an object. - If
group1
exists, use H5L_EXISTS again, this time with name
set to group1/group2
, to verify that the link group2
exists in group1
. - If the
group2
link exists, use H5O_EXISTS_BY_NAME to verify that group1/group2
resolves to an object. - If
group2
exists, use H5L_EXISTS again, this time with name
set to group1/group2/softlink_to_group3
, to verify that the link softlink_to_group3
exists in group2
. - If the
softlink_to_group3
link exists, use H5O_EXISTS_BY_NAME to verify that group1/group2/softlink_to_group3
resolves to an object. - If
softlink_to_group3
exists, you can now safely use H5L_EXISTS with name
set to group1/group2/softlink_to_group3/datasetD
to verify that the target link, datasetD
, exists. - And finally, if the link
datasetD
exists, use H5O_EXISTS_BY_NAME to verify that group1/group2/softlink_to_group3/datasetD
resolves to an object.
If the link to be verified is specified with an absolute path, the same approach should be used, but starting with the first link in the file’s root group. For instance, if datasetD
were in /group1/group2/softlink_to_group3
, the first call to H5L_EXISTS would have name
set to /group1
.
Note that this is an outline and does not include all necessary details. Depending on circumstances, for example, an application may need to verify the type of an object also.
Returns:
Returns a positive value if the object pointed to by the loc_id
and name
combination exists.
Returns 0 if the object pointed to by the loc_id
and name
combination does not exist.
Returns a negative value when the function fails.
Example:
History:
Release | Change |
---|
1.8.11 | Fortran subroutine introduced in this release. |
1.8.5 | C function introduced in this release. |
--- Last Modified: April 25, 2019 | 01:20 PM