- Created by Mike McGreevy, last modified by Barbara Jones on Apr 25, 2019
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Determine whether a link with the specified name exists in a group
H5L_EXISTS(loc_id, name, lapl_id)
htri_t H5Lexists( hid_t loc_id, const char *name, hid_t lapl_id )
SUBROUTINE h5lexists_f(loc_id, name, link_exists, hdferr, lapl_id) IMPLICIT NONE INTEGER(HID_T), INTENT(IN) :: loc_id ! Identifier of file or group to query. CHARACTER(LEN=*), INTENT(IN) :: name ! Link name to check. LOGICAL, INTENT(OUT) :: link_exists ! .TRUE. if exists, .FALSE. otherwise INTEGER, INTENT(OUT) :: hdferr ! Error code: ! 0 on success and -1 on failure INTEGER(HID_T), OPTIONAL, INTENT(IN) :: lapl_id ! Link access property list identifier. END SUBROUTINE h5lexists_f
|hid_t ||IN: Location identifier of link to query; may be a file, group, dataset, named datatype or attribute identifier|
|const char *||IN: The name of the link to check|
|hid_t ||IN: Link access property list identifier|
H5L_EXISTS allows an application to determine whether the link
name exists in the location specified by
loc_id. The link may be of any type; only the presence of a link with that name is checked.
Note that H5L_EXISTS verifies only that the target link 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, H5L_EXISTS 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 is a member of the group specified by
- First use
H5Lexiststo verify that
H5Lexistsagain, this time with
group1/group2, to verify that
group1/group2/softlink_to_group3to verify that
softlink_to_group3exists, you can now safely use H5L_EXISTS with
group1/group2/softlink_to_group3/datasetDto verify that the target link,
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
Note that this is an outline and does not include all necessary details. Depending on circumstances, for example, you may need to verify that an intermediate link points to a group and that a soft link points to an existing target.
The behavior of H5L_EXISTS was changed in the 1.10 release in the case where the root group, “/”, is the name of the link. This change is described below:
- Let ‘file’ denote a valid HDF5 file identifier, and let ‘lapl’ denote a valid link access property list identifier. A call to H5L_EXISTS with arguments ‘file’, “/”, and ‘lapl’ returns a positive value; in other words,
H5Lexists(file, "/", lapl)returns a positive value. In HDF5 version 1.8.16, this function returns 0.
- Let ‘root’ denote a valid HDF5 group identifier that refers to the root group of an HDF5 file, and let ‘lapl’ denote a valid link access property list identifier. A call to H5L_EXISTS with arguments ‘root’, “/”, and ‘lapl’ returns a positive value; in other words,
H5Lexists(root, "/", lapl)returns a postive value. In HDF5 version 1.8.16, this function returns 0.
Note that the function accepts link names and path names. This is potentially misleading to callers, and we plan to separate the functionality for link names and path names in a future release.
Returns a positive value if the link exists.
Returns 0 if the link does not exist.
Returns a negative value when the function fails and may return a negative value if the link does not exist. See “Failure Modes” below.
H5L_EXISTS checks the existence of only the final element in a relative or absolute path; it does not check any other path elements. The function will therefore fail when both of the following conditions exist:
nameis not local to the group specified by
loc_idis something other than a group identifier,
nameis not local to the root group.
- Any element of the relative path or absolute path in
name, except the target link, does not exist.
|1.10.0||Function behavior changed in this release. See the “Note on Behavior Change” section above.|
|1.8.0||Function introduced in this release.|
--- Last Modified: April 25, 2019 | 12:41 PM