1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
|
<html>
<head><title>
HDF5/H5G Draft API Specification
</title></head>
<body>
<hr>
<center>
<a href="RM_H5Front.html">HDF5 Reference Manual</a>
<a href="RM_H5.html">H5</a>
<a href="RM_H5A.html">H5A</a>
<a href="RM_H5D.html">H5D</a>
<a href="RM_H5E.html">H5E</a>
<a href="RM_H5F.html">H5F</a>
H5G
<a href="RM_H5P.html">H5P</a>
<a href="RM_H5S.html">H5S</a>
<a href="RM_H5T.html">H5T</a>
<a href="RM_H5Z.html">H5Z</a>
<a href="Tools.html">Tools</a>
<!--
<a href="Glossary.html">Glossary</a>
-->
</center>
<hr>
<center>
<h1>H5G: Group Interface</h1>
</center>
<h2>Group Object API Functions</h2>
The Group interface functions create and manipulate physical groups
of objects on disk.
<table border=0>
<tr><td valign=top>
<ul>
<li><a href="#Group-Create">H5Gcreate</a>
<li><a href="#Group-Open">H5Gopen</a>
<li><a href="#Group-Set">H5Gset</a>
<li><a href="#Group-Close">H5Gclose</a>
<li><a href="#Group-Push">H5Gpush</a>
</ul>
</td><td> </td><td valign=top>
<ul>
<li><a href="#Group-Pop">H5Gpop</a>
<li><a href="#Group-Link">H5Glink</a>
<li><a href="#Group-Unlink">H5Gunlink</a> (NYI)
<li><a href="#Group-Iterate">H5Giterate</a>
<li><a href="#Group-Move">H5Gmove</a> (NYI)
</ul>
</td><td> </td><td valign=top>
<ul>
<li><a href="#Group-GetObjinfo">H5Gget_objinfo</a>
<li><a href="#Group-GetLinkval">H5Gget_linkval</a>
<li><a href="#Group-SetComment">H5Gset_comment</a>
<li><a href="#Group-GetComment">H5Gget_comment</a>
</ul>
</td></tr><tr><td colspan=5 align=right>
<font size=-2>(NYI = Not yet implemented)</font>
</td></tr>
</table>
<p>
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 boot block.
<p>
Every file identifier returned by <code>H5Fcreate</code> or
<code>H5Fopen</code> maintains an independent current working group
stack, the top item of which is the current working group. The
stack can be manipulated with <code>H5Gset</code>, <code>H5Gpush</code>,
and <code>H5Gpop</code>. The root object is the current working group
if the stack is empty.
<p>
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 with the current working group.
<p>
The library does not maintain the full absolute name of its current
working group because (1) cycles in the graph can make the name length
unbounded and (2) a group does not necessarily have a unique name. A
more Unix-like hierarchical naming scheme can be implemented on top of
the directed graph scheme by creating a ".." entry in each group that
points to its single predecessor; a <code>getcwd</code> function would
then be trivial.
<hr>
<dl>
<dt><strong>Name:</strong> <a name="Group-Create">H5Gcreate</a>
<dt><strong>Signature:</strong>
<dd><em>hid_t </em><code>H5Gcreate</code>(<em>hid_t</em> <code>loc_id</code>,
<em>const char *</em><code>name</code>,
<em>size_t</em> <code>size_hint</code>
)
<dt><strong>Purpose:</strong>
<dd>Creates a new empty group and gives it a name.
<dt><strong>Description:</strong>
<dd><code>H5Gcreate</code> creates a new group with the specified
name at the specified location, <code>loc_id</code>.
The location is identified by a file or group identifier.
The name, <code>name</code>, must not already be taken by some
other object and all parent groups must already exist.
<p>
<code>size_hint</code> 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 <code>size_hint</code>
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.
<p>
The return value is a group identifier for the open group.
This group identifier should be closed by calling
<code>H5Gclose()</code> when it is no longer needed.
<dt><strong>Parameters:</strong>
<dl>
<dt><em>hid_t</em> <code>loc_id</code>
<dd>The file or group identifier.
<dt><em>const char *</em><code>name</code>
<dd>The absolute or relative name of the new group.
<dt><em>size_t</em> <code>size_hint</code>
<dd>An optional parameter indicating the number of bytes
to reserve for the names that will appear in the group.
A conservative estimate could result in multiple
system-level I/O requests to read the group name heap;
a liberal estimate could result in a single large
I/O request even when the group has just a few names.
HDF5 stores each name with a null terminator.
</dl>
<dt><strong>Returns:</strong>
<dd>Returns a valid group identifier for the open group if successful;
otherwise FAIL (-1).
</dl>
<hr>
<dl>
<dt><strong>Name:</strong> <a name="Group-Open">H5Gopen</a>
<dt><strong>Signature:</strong>
<dd><em>hid_t </em><code>H5Gopen</code>(<em>hid_t</em> <code>loc_id</code>,
<em>const char *</em><code>name</code>
)
<dt><strong>Purpose:</strong>
<dd>Opens an existing group for modification and returns a group
identifier for that group.
<dt><strong>Description:</strong>
<dd><code>H5Gopen</code> opens an existing group with the specified name at
the specified location, <code>loc_id</code>.
The location is identified by a file or
group identifier, and returns a group identifier for the group.
The obtained group identifier should be released by calling
<code>H5Gclose()</code> when it is no longer needed.
<dt><strong>Parameters:</strong>
<dl>
<dt><em>hid_t</em> <code>loc_id</code>
<dd>File or group identifier within which group is to be open.
<dt><em>const char *</em> <code>name</code>
<dd>Name of group to open.
</dl>
<dt><strong>Returns:</strong>
<dd>Returns a valid group identifier if successful;
otherwise FAIL (-1).
</dl>
<hr>
<dl>
<dt><strong>Name:</strong> <a name="Group-Set">H5Gset</a>
<dt><strong>Signature:</strong>
<dd><em>herr_t </em><code>H5Gset</code> (<em>hid_t</em> <code>loc_id</code>,
<em>const char *</em><code>name</code>
)
<dt><strong>Purpose:</strong>
<dd>Sets the current working group within a file.
<dt><strong>Description:</strong>
<dd><code>H5Gset</code> sets the group with the specified name
to be the current working group for the file which contains it.
This function sets the current working group by modifying the
top element of the current working group stack or, if the
stack is empty, by pushing a new element onto the stack.
The initial current working group is the root group.
<p>
<code>loc_id</code> can be a file identifier or a group identifier.
<p>
<code>name</code> is an absolute or relative name and is resolved as follows. Each file identifier
has a current working group, initially the root group of the
file. Relative names do not begin with a slash and are relative
to the specified group or to the current working group.
Absolute names begin with a slash and are relative to the file's
root group. For instance, the name <code>/Foo/Bar/Baz</code> is
resolved by first looking up <code>Foo</code> in the root group;
the name <code>Foo/Bar/Baz</code> is resolved by first looking
up the name <code>Foo</code> in the current working group.
<p>
Each file identifier maintains its own notion of the current
working group. If <code>loc_id</code> is a group identifier, the
file identifier is derived from the group identifier.
<p>
If a single file is opened with multiple calls to <code>H5Fopen()</code>,
which would return multiple file identifiers, then each
identifier's current working group can be set independently
of the other file identifiers for that file.
<dt><strong>Parameters:</strong>
<dl>
<dt><em>hid_t</em> <code>loc_id</code>
<dd>The file or group identifier.
<dt><em>const char *</em><code>name</code>
<dd>The name of the new current working group.
</dl>
<dt><strong>Returns:</strong>
<dd>Returns SUCCEED (0) if successful;
otherwise FAIL (-1).
</dl>
<hr>
<dl>
<dt><strong>Name:</strong> <a name="Group-Push">H5Gpush</a>
<dt><strong>Signature:</strong>
<dd><em>herr_t </em><code>H5Gpush</code> (<em>hid_t</em> <code>loc_id</code>,
<em>const char *</em><code>name</code>
)
<dt><strong>Purpose:</strong>
<dd>Sets the current working group by pushing a
new element onto the current working group stack.
<dt><strong>Description:</strong>
<dd>Each file identifier maintains a stack of groups, the top group
of which is the current working group. The stack initially
contains only the root group. <code>H5Gpush</code> pushes a new group
onto the stack, thus setting a new current working group.
<dt><strong>Parameters:</strong>
<dl>
<dt><em>hid_t</em> <code>loc_id</code>
<dd>File or group identifier.
<dt><em>const char *</em><code>name</code>
<dd>The name of the new current working group. The name may be
an absolute or relative name.
</dl>
<dt><strong>Returns:</strong>
<dd>Returns SUCCEED (0) if successful;
otherwise FAIL (-1).
</dl>
<hr>
<dl>
<dt><strong>Name:</strong> <a name="Group-Pop">H5Gpop</a>
<dt><strong>Signature:</strong>
<dd><em>herr_t </em><code>H5Gpop</code> (<em>hid_t</em> <code>loc_id</code>)
<dt><strong>Purpose:</strong>
<dd>Removes the top, or latest, entry from the working group stack,
setting the current working group to the previous value.
<dt><strong>Description:</strong>
<dd><code>H5Gpop</code> restores the previous current working group by
popping an element from the current working group stack.
An empty stack implies that the current working group is the root
object. Attempting to pop an empty stack results in failure.
<p>
Each file identfier maintains its own notion of the current
working group. That is, if a single file is opened with
multiple calls to <code>H5Fopen()</code>, which returns multiple file
handles, then each identfier's current working group can be
set independently of the other file identfiers for that file.
<p>
If <code>loc_id</code> is a group identifier, it is used only to determine the
file identifier for the stack from which to pop the top entry.
<dt><strong>Parameters:</strong>
<dl>
<dt><em>hid_t</em> <code>loc_id</code>
<dd>The file, group, dataset, or datatype identifier.
</dl>
<dt><strong>Returns:</strong>
<dd>Returns SUCCEED (0) if successful;
otherwise FAIL (-1).
</dl>
<hr>
<dl>
<dt><strong>Name:</strong> <a name="Group-Close">H5Gclose</a>
<dt><strong>Signature:</strong>
<dd><em>herr_t </em><code>H5Gclose</code>(<em>hid_t </em><code>group_id</code>)
<dt><strong>Purpose:</strong>
<dd>Closes the specified group.
<dt><strong>Description:</strong>
<dd><code>H5Gclose</code> releases resources used by a group which was
opened by <code>H5Gcreate()</code> or <code>H5Gopen()</code>.
After closing a group, the <code>group_id</code> cannot be used again.
<p>
Failure to release a group with this call will result in resource leaks.
<dt><strong>Parameters:</strong>
<dl>
<dt><em>hid_t</em> <code>group_id</code>
<dd>Group identifier to release.
</dl>
<dt><strong>Returns:</strong>
<dd>Returns SUCCEED (0) if successful;
otherwise FAIL (-1).
</dl>
<hr>
<dl>
<dt><strong>Name:</strong> <a name="Group-Link">H5Glink</a>
<dt><strong>Signature:</strong>
<dd><em>herr_t</em> <code>H5Glink</code>(<em>hid_t</em> <code>loc_id</code>,
<em>H5G_link_t</em> <code>link_type</code>,
<em>const char *</em><code>current_name</code>,
<em>const char *</em><code>new_name</code>
)
<dt><strong>Purpose:</strong>
<dd>Creates a link of the specified type from <code>new_name</code>
to <code>current_name</code>.
<dt><strong>Description:</strong>
<dd><code>H5Glink</code> creates a new name for an object that has some current
name, possibly one of many names it currently has.
<p>
If <code>link_type</code> is <code>H5G_LINK_HARD</code>, then
<code>current_name</code> must name an existing object and both
names are interpreted relative to <code>loc_id</code>, which is
either a file identifier or a group identifier.
<p>
If <code>link_type</code> is <code>H5G_LINK_SOFT</code>, then
<code>current_name</code> can be anything and is interpreted at
lookup time relative to the group which contains the final
component of <code>new_name</code>. For instance, if
<code>current_name</code> is <code>./foo</code>,
<code>new_name</code> is <code>./x/y/bar</code>, and a request
is made for <code>./x/y/bar</code>, then the actual object looked
up is <code>./x/y/./foo</code>.
<dt><strong>Parameters:</strong>
<dl>
<dt><em>hid_t</em> <code>loc_id</code>
<dd>File, group, dataset, or datatype identifier.
<dt><em>H5G_link_t</em> <code>link_type</code>
<dd>Link type.
Possible values are <code>H5G_LINK_HARD</code> and <code>H5G_LINK_SOFT</code>.
<dt><em>const char *</em> <code>current_name</code>
<dd>Name of the existing object if link is a hard link.
Can be anything for the soft link.
<dt><em>const char *</em> <code>new_name</code>
<dd>New name for the object.
</dl>
<dt><strong>Returns:</strong>
<dd>Returns SUCCEED (0) if successful;
otherwise FAIL (-1).
</dl>
<hr>
<dl>
<dt><strong>Name:</strong> <a name="Group-Unlink">H5Gunlink</a>
<strong>(Not implemented in this release.)</strong>
<dt><strong>Signature:</strong>
<dd><em>herr_t </em><code>H5Gunlink</code>(<em>hid_t</em> <code>loc_id</code>,
<em>const char *</em><code>name</code>
)
<dt><strong>Purpose:</strong>
<dd>Removes the specified <code>name</code> from the group graph and
decrements the link count for the object to which <code>name</code> points
<dt><strong>Description:</strong>
<dd><code>H5Gunlink</code> removes an association between a name and an object.
Object headers keep track of how many hard links refer to the object;
when the hard 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.
<p>
If the link count reaches zero, all file-space associated with
the object will be reclaimed. If the object is open, the
reclamation of the file space is delayed until all handles to the
object are closed.
<dt><strong>Parameters:</strong>
<dl>
<dt><em>hid_t</em> <code>loc_id</code>
<dd>Identifier of the file containing the object.
<dt><em>const char *</em> <code>name</code>
<dd>Name of the object to unlink.
</dl>
<dt><strong>Returns:</strong>
<dd>Returns SUCCEED (0) if successful;
otherwise FAIL (-1).
</dl>
<hr>
<dl>
<dt><strong>Name:</strong> <a name="Group-Iterate">H5Giterate</a>
<dt><strong>Signature:</strong>
<dd><em>int</em> <code>H5Giterate</code>(<em>hid_t</em> <code>loc_id</code>,
<em>const char</em> <code>*name</code>,
<em>int</em> <code>*idx</code>,
<em>H5G_operator_t</em> <code>operator</code>,
<em>void</em> <code>*operator_data</code>
)
<dt><strong>Purpose:</strong>
<dd>Iterates an operation over the entries of a group.
<dt><strong>Description:</strong>
<dd><code>H5Giterate</code> iterates over the members of
<code>name</code> in the file or group specified with
<code>loc_id</code>.
For each object in the group, the <code>operator_data</code>
and some additional information, specified below, are
passed to the <code>operator</code> function.
The iteration begins with the <code>idx</code> object in the
group and the next element to be processed by the operator is
returned in <code>idx</code>. If <code>idx</code>
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.
<p>
The prototype for <code>H5G_operator_t</code> is:
<ul><dl>
<dd><code>typedef</code> <em>herr_t *</em>(<code>H5G_operator_t</code>)(<em>hid_t</em> <code>group_id</code>,
<em>const char *</em><code>member_name</code>, <em>void *</em><code>operator_data/*in,out*/</code>);
</dl></ul>
<dd>The operation receives the group identifier for the group being
iterated over, <code>group_id</code>, the name of the current
object within the group, <code>member_name</code>, and the
pointer to the operator data passed in to <code>H5Giterate</code>,
<code>operator_data</code>.
<p>
The return values from an operator are:
<ul>
<li>Zero causes the iterator to continue, returning
zero when all group members have been processed.
<li>Positive causes the iterator to immediately return that positive
value, indicating short-circuit success. The iterator can be
restarted at the next group member.
<li>Negative causes the iterator to immediately return that value,
indicating failure. The iterator can be restarted at the next
group member.
</ul>
<dt><strong>Parameters:</strong>
<dl>
<dt><em>hid_t</em> <code>loc_id</code>
<dd>IN: File or group identifier.
<dt><em>const char</em> <code>*name</code>
<dd>IN: Group over which the iteration is performed.
<dt><em>int</em> <code>*idx</code>
<dd>IN/OUT: Location at which to begin the iteration.
<dt><em>H5G_iterate_t</em> <code>operator</code>
<dd>IN: Operation to be performed on an object at each step of
the iteration.
<dt><em>void</em> <code>*operator_data</code>
<dd>IN/OUT: Data associated with the operation.
</dl>
<dt><strong>Returns:</strong>
<dd>Returns the return value of the last operator if it was non-zero,
or zero if all group members were processed.
Otherwise, returns FAIL (-1).
</dl>
<hr>
<dl>
<dt><strong>Name:</strong> <a name="Group-Move">H5Gmove</a>
<strong>(Not implemented in this release.)</strong>
<dt><strong>Signature:</strong>
<dd><em>herr_t</em> <code>H5Gmove</code>(<em>hid_t</em> <code>loc_id</code>,
<em>const char</em> <code>*src</code>,
<em>const char</em> <code>*dst</code>
)
<dt><strong>Purpose:</strong>
<dd>Renames an object within an HDF5 file.
<dt><strong>Description:</strong>
<dd><code>H5Gmove</code> renames an object within an HDF5 file.
The original name, <code>src</code>, is unlinked from the
group graph and the new name, <code>dst</code>, is inserted
as an atomic operation. Both names are interpreted relative
to <code>loc_id</code>, which is either a file or a group
identifier.
<dt><strong>Parameters:</strong>
<dl>
<dt><em>hid_t</em> <code>loc_id</code>
<dd>File or group identifier.
<dt><em>const char</em> <code>*src</code>
<dd>Object's original name.
<dt><em>const char</em> <code>*dst</code>
<dd>Object's new name.
</dl>
<dt><strong>Returns:</strong>
<dd>Returns SUCCEED (0) if successful;
otherwise FAIL (-1).
</dl>
<hr>
<dl>
<dt><strong>Name:</strong> <a name="Group-GetObjinfo">H5Gget_objinfo</a>
<dt><strong>Signature:</strong>
<dd><em>herr_t</em> <code>H5Gget_objinfo</code>(<em>hid_t</em> <code>loc_id</code>,
<em>const char *</em><code>name</code>,
<em>hbool_t</em> <code>follow_link</code>,
<em>H5G_stat_t *</em><code>statbuf</code>
)
<dt><strong>Purpose:</strong>
<dd>Returns information about an object.
<dt><strong>Description:</strong>
<dd><code>H5Gget_objinfo</code> returns information about the
specified object through the <code>statbuf</code> argument.
<code>loc_id</code> (a file, group, or dataset identifier) and
<code>name</code> together determine the object.
If the object is a symbolic link and <code>follow_link</code> is
zero (<code>0</code>), 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 <code>follow_link</code> is non-zero but the final symbolic link
is dangling (does not point to anything), then an error is returned.
The <code>statbuf</code> fields are undefined for an error.
The existence of an object can be tested by calling this function
with a null <code>statbuf</code>.
<p>
<code>H5Gget_objinfo()</code> fills in the following data structure:
<pre>
typedef struct H5G_stat_t {
unsigned long fileno[2];
unsigned long objno[2];
unsigned nlink;
H5G_obj_t type;
time_t mtime;
size_t linklen;
} H5G_stat_t
</pre>
The <code>fileno</code> and <code>objno</code> fields contain
four values which uniquely itentify an object among those
HDF5 files which are open: if all four values are the same
between two objects, then the two objects are the same
(provided both files are still open).
The <code>nlink</code> 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 <code>type</code> field contains the type of the object,
one of <code>H5G_GROUP</code>, <code>H5G_DATASET</code>,
or <code>H5G_LINK</code>.
The <code>mtime</code> field contains the modification time.
If information is being returned about a symbolic link then
<code>linklen</code> will be the length of the link value
(the name of the pointed-to object with the null terminator);
otherwise <code>linklen</code> will be zero.
Other fields may be added to this structure in the future.
<dt><strong>Note:</strong>
<dd>Some systems will be able to record the time accurately but
unable to retrieve the correct time; such systems (e.g., Irix64)
will report an <code>mtime</code> value of 0 (zero).
<dt><strong>Parameters:</strong>
<dl>
<dt><em>hid_t</em> <code>loc_id</code>
<dd>IN: File, group, dataset, or datatype identifier.
<dt><em>const char</em> <code>*name</code>
<dd>IN: Name of the object for which status is being sought.
<dt><em>hbool_t</em> <code>follow_link</code>
<dd>IN: Link flag.
<dt><em>H5G_stat_t</em> <code>*statbuf</code>
<dd>OUT: Buffer in which to return information about the object.
</dl>
<dt><strong>Returns:</strong>
<dd> Returns SUCCEED (0) with the fields of <code>statbuf</code>
(if non-null) initialized.
Otherwise returns FAIL (-1).
</dl>
<hr>
<dl>
<dt><strong>Name:</strong> <a name="Group-GetLinkval">H5Gget_linkval</a>
<dt><strong>Signature:</strong>
<dd><em>herr_t</em> <code>H5Gget_linkval</code>(<em>hid_t</em> <code>loc_id</code>,
<em>const char *</em><code>name</code>,
<em>size_t</em> <code>size</code>,
<em>char *</em><code>value</code>
)
<dt><strong>Purpose:</strong>
<dd>Returns link value.
<dt><strong>Description:</strong>
<dd><code>H5Gget_linkval</code> returns <code>size</code>
characters of the link value through the <code>value</code>
argument if <code>loc_id</code> (a file or group identifier)
and <code>name</code> specify a symbolic link.
If <code>size</code> is smaller than the link value, then
<code>value</code> will not be null terminated.
<p>
This function fails if the specified object is not a symbolic link.
The presence of a symbolic link can be tested by passing zero for
<code>size</code> and NULL for <code>value</code>.
<p>
Use <code>H5Gget_objinfo()</code> to get the size of a link value.
<dt><strong>Parameters:</strong>
<dl>
<dt><em>hid_t</em> <code>loc_id</code>
<dd>IN: Identifier of the file, group, dataset, or datatype.
<dt><em>const char *</em><code>name</code>
<dd>IN: Name of the object whose link value is to be checked.
<dt><em>size_t</em> <code>size</code>
<dd>IN: Maximum number of characters of <code>value</code>
to be returned.
<dt><em>char *</em><code>value</code>
<dd>OUT: Link value.
</dl>
<dt><strong>Returns:</strong>
<dd>Returns SUCCEED (0), with the link value in <code>value</code>,
if successful.
Otherwise returns FAIL (-1).
</dl>
<hr>
<dl>
<dt><strong>Name:</strong> <a name="Group-SetComment">H5Gset_comment</a>
<dt><strong>Signature:</strong>
<dd><em>herr_t</em> <code>H5Gset_comment</code>(<em>hid_t</em> <code>loc_id</code>,
<em>const char *</em><code>name</code>,
<em>const char *</em><code>comment</code>
)
<dt><strong>Purpose:</strong>
<dd>Sets comment for specified object.
<dt><strong>Description:</strong>
<dd><code>H5Gset_comment</code> sets the comment for the the
object <code>name</code> to <code>comment</code>.
Any previously existing comment is overwritten.
<p>
If <code>comment</code> is the empty string or a
null pointer, the comment message is removed from the object.
<p>
Comments should be relatively short, null-terminated,
ASCII strings.
<p>
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.
<dt><strong>Parameters:</strong>
<dl>
<dt><em>hid_t</em> <code>loc_id</code>
<dd>IN: Identifier of the file, group, dataset, or datatype.
<dt><em>const char *</em><code>name</code>
<dd>IN: Name of the object whose comment is to be set or reset.
<dt><em>const char *</em><code>comment</code>
<dd>IN: The new comment.
</dl>
<dt><strong>Returns:</strong>
<dd>Returns SUCCEED (0) if successful;
otherwise returns FAIL (-1).
</dl>
<hr>
<dl>
<dt><strong>Name:</strong> <a name="Group-GetComment">H5Gget_comment</a>
<dt><strong>Signature:</strong>
<dd><em>herr_t</em> <code>H5Gget_comment</code>(<em>hid_t</em> <code>loc_id</code>,
<em>const char *</em><code>name</code>,
<em>size_t</em> <code>bufsize</code>,
<em>char *</em><code>comment</code>
)
<dt><strong>Purpose:</strong>
<dd>Retrieves comment for specified object.
<dt><strong>Description:</strong>
<dd><code>H5Gget_comment</code> retrieves the comment for the the
object <code>name</code>. The comment is returned in the buffer
<code>comment</code>.
<p>
At most <code>bufsize</code> characters, including a null
terminator, are copied. The result is not null terminated
if the comment is longer than the supplied buffer.
<p>
If an object does not have a comment, the empty string
is returned.
<dt><strong>Parameters:</strong>
<dl>
<dt><em>hid_t</em> <code>loc_id</code>
<dd>IN: Identifier of the file, group, dataset, or datatype.
<dt><em>const char *</em><code>name</code>
<dd>IN: Name of the object whose comment is to be set or reset.
<dt><em>size_t</em> <code>bufsize</code>
<dd>IN: Anticipated size of the buffer required to hold
<code>comment</code>.
<dt><em>char *</em><code>comment</code>
<dd>OUT: The comment.
</dl>
<dt><strong>Returns:</strong>
<dd>Returns the number of characters in the comment,
counting the null terminator, if successful; the value
returned may be larger than <code>bufsize</code>.
Otherwise returns FAIL (-1).
</dl>
<hr>
<center>
<a href="RM_H5Front.html">HDF5 Reference Manual</a>
<a href="RM_H5.html">H5</a>
<a href="RM_H5A.html">H5A</a>
<a href="RM_H5D.html">H5D</a>
<a href="RM_H5E.html">H5E</a>
<a href="RM_H5F.html">H5F</a>
H5G
<a href="RM_H5P.html">H5P</a>
<a href="RM_H5S.html">H5S</a>
<a href="RM_H5T.html">H5T</a>
<a href="RM_H5Z.html">H5Z</a>
<a href="Tools.html">Tools</a>
<!--
<a href="Glossary.html">Glossary</a>
-->
</center>
<hr>
<address>
<a href="mailto:hdfhelp@ncsa.uiuc.edu">HDF Help Desk</a>
<br>
Last modified: 2 September 1998
</body>
</html>
|
