summaryrefslogtreecommitdiffstats
path: root/doc/src/RM_H5A.html
blob: 0c236dae4095b9e78b1892041469f1a3a27af734 (plain)
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
<html>
<head><title>
HDF5/H5A Draft API Specification
</title></head>

<body>

<hr>
<center>
<a href="RM_H5Front.html">HDF5 Reference Manual</a>&nbsp;
<a href="RM_H5.html">H5</a>&nbsp;&nbsp;
H5A&nbsp;&nbsp;
<a href="RM_H5D.html">H5D</a>&nbsp;&nbsp;
<a href="RM_H5E.html">H5E</a>&nbsp;&nbsp;
<a href="RM_H5F.html">H5F</a>&nbsp;&nbsp;
<a href="RM_H5G.html">H5G</a>&nbsp;&nbsp;
<a href="RM_H5P.html">H5P</a>&nbsp;&nbsp;
<a href="RM_H5S.html">H5S</a>&nbsp;&nbsp;
<a href="RM_H5T.html">H5T</a>&nbsp;&nbsp;
<a href="RM_H5Z.html">H5Z</a>&nbsp;&nbsp;
<a href="Glossary.html">Glossary</a>
</center>
<hr>

<center>
<h1>H5A: Attribute Interface</h1>
</center>

<h2>Attribute API Functions</h2>

These functions create and manipulate attributes 
and information about attributes.

<table border=0>
<tr><td valign=top>
<ul>
    <li><a href="#Annot-Create">H5Acreate</a>
    <li><a href="#Annot-Write">H5Awrite</a>
    <li><a href="#Annot-Read">H5Aread</a>
    <li><a href="#Annot-Close">H5Aclose</a>
</ul>
</td><td>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</td><td valign=top>
<ul>
    <li><a href="#Annot-GetName">H5Aget_name</a>
    <li><a href="#Annot-OpenName">H5Aopen_name</a>
    <li><a href="#Annot-OpenIdx">H5Aopen_idx</a>
    <li><a href="#Annot-GetSpace">H5Aget_space</a>
</ul>
</td><td>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</td><td valign=top>
<ul>
    <li><a href="#Annot-GetType">H5Aget_type</a>
    <li><a href="#Annot-NumAttrs">H5Anum_attrs</a>
    <li><a href="#Annot-Iterate">H5Aiterate</a>
    <li><a href="#Annot-Delete">H5Adelete</a>
</ul>
</td></tr>
</table>

<p>
The Attribute interface, H5A, is primarily designed to easily allow 
small datasets to be attached to primary datasets as metadata information. 
Additional goals for the H5A interface include keeping storage requirement 
for each attribute to a minimum and easily sharing attributes among 
datasets. 
<p>
Because attributes are intended to be small objects, large datasets 
intended as additional information for a primary dataset should be 
stored as supplemental datasets in a group with the primary dataset. 
Attributes can then be attached to the group containing everything 
to indicate a particular type of dataset with supplemental datasets 
is located in the group. How small is "small" is not defined by the 
library and is up to the user's interpretation. 
<p>
See <a href="Attributes.html"><cite>Attributes</cite></a> in the
<a href="H5.user.html"><cite>HDF5 User's Guide</cite></a> for further information.

<hr>
<dl>
<dt><strong>Name:</strong> <a name="Annot-Create">H5Acreate</a>
<dt><strong>Signature:</strong>
    <dd><em>hid_t</em> <code>H5Acreate</code>(<em>hid_t</em> <code>loc_id</code>,
        <em>const char *</em><code>name</code>,
        <em>hid_t</em> <code>type_id</code>,
        <em>hid_t</em> <code>space_id</code>,
        <em>hid_t</em> <code>create_plist</code>
    )
<dt><strong>Purpose:</strong>
    <dd>Creates a dataset as an attribute of another group, dataset, 
        or named datatype.
<dt><strong>Description:</strong>
    <dd><code>H5Acreate</code> creates an attribute which is attached 
        to the object specified with <code>loc_id</code>.  
        <code>loc_id</code> is an identifier of a group, dataset, 
        or named datatype.  The name specified with <code>name</code>
        for each attribute for an object must be unique for that object.  
        The datatype and dataspace identifiers of the attribute, 
        <code>type_id</code> and <code>space_id</code>, respectively, 
        are created with the H5T and H5S interfaces, respectively.  
        Currently only simple dataspaces are allowed for attribute
        dataspaces.  The <code>create_plist_id</code> property list 
        is currently unused, but will be used int the future for optional 
        properties of attributes.  The attribute identifier returned from 
        this function must be released with <code>H5Aclose</code> or 
        resource leaks will develop.  Attempting to create an attribute 
        with the same name as an already existing attribute will fail,
        leaving the pre-existing attribute in place.
<dt><strong>Parameters:</strong>
    <dl>
        <dt><em>hid_t</em> <code>loc_id</code>
            <dd>IN: Object (dataset or group) to be attached to.
        <dt><em>const char *</em><code>name</code>
            <dd>IN: Name of attribute to create.
        <dt><em>hid_t</em> <code>type_id</code>
            <dd>IN: Identifier of datatype for attribute.
        <dt><em>hid_t</em> <code>space_id</code>
            <dd>IN: Identifier of dataspace for attribute.
        <dt><em>hid_t</em> <code>create_plist</code>
            <dd>IN: Identifier of creation property list (currently not used).
    </dl>
<dt><strong>Returns:</strong>
    <dd>Returns an attribute identifier if successful;
        otherwise FAIL (-1).
</dl>


<hr>
<dl>
<dt><strong>Name:</strong> <a name="Annot-OpenName">H5Aopen_name</a>
<dt><strong>Signature:</strong>
    <dd><em>hid_t</em> <code>H5Aopen_name</code>(<em>hid_t</em> <code>loc_id</code>,
        <em>const char *</em><code>name</code>
    )
<dt><strong>Purpose:</strong>
    <dd> Opens an attribute specified by name.
<dt><strong>Description:</strong>
    <dd><code>H5Aopen_name</code> opens an attribute specified by 
         its name, <code>name</code>, which is attached to the 
         object specified with <code>loc_id</code>. 
         The location object may be either a group, dataset, or 
         named datatype, which may have any sort of attribute. 
         The attribute identifier returned from this function must 
         be released with <code>H5Aclose</code> or resource leaks 
         will develop. 
<dt><strong>Parameters:</strong>
    <dl>
        <dt><em>hid_t</em> <code>loc_id</code>
            <dd>IN: Identifier of a group, dataset, or named datatype 
                atttribute to be attached to.
        <dt><em>const char *</em><code>name</code>
            <dd>IN: Attribute name.
    </dl>
<dt><strong>Returns:</strong>
    <dd>Returns attribute identifier if successful;
        otherwise FAIL (-1).
</dl>


<hr>
<dl>
<dt><strong>Name:</strong> <a name="Annot-OpenIdx">H5Aopen_idx</a>
<dt><strong>Signature:</strong>
    <dd><em>hid_t</em> <code>H5Aopen_idx</code>(<em>hid_t</em> <code>loc_id</code>,
        <em>unsigned int</em> <code>idx</code>
    )
<dt><strong>Purpose:</strong>
    <dd>Opens the attribute specified by its index.
<dt><strong>Description:</strong>
    <dd><code>H5Aopen_idx</code> opens an attribute which is attached 
        to the object specified with <code>loc_id</code>. 
        The location object may be either a group, dataset, or 
        named datatype, all of which may have any sort of attribute.  
        The attribute specified by the index, <code>idx</code>, 
        indicates the attribute to access.  
        The value of <code>idx</code> is a 0-based, non-negative integer.
        The attribute identifier returned from this function must be 
        released with <code>H5Aclose</code> or resource leaks will develop. 
<dt><strong>Parameters:</strong>
    <dl>
        <dt><em>hid_t</em> <code>loc_id</code>
            <dd>IN: Identifier of the group, dataset, or named datatype 
                attribute to be attached to.
        <dt><em>unsigned int</em> <code>idx</code>
            <dd>IN: Index of the attribute to open.
    </dl>
<dt><strong>Returns:</strong>
    <dd>Returns attribute identifier if successful;
        otherwise FAIL (-1).
</dl>


<hr>
<dl>
<dt><strong>Name:</strong> <a name="Annot-Write">H5Awrite</a>
<dt><strong>Signature:</strong>
    <dd><em>herr_t</em> <code>H5Awrite</code>(<em>hid_t</em> <code>attr_id</code>,
        <em>hid_t</em> <code>mem_type_id</code>,
        <em>void *</em><code>buf</code>
    )
<dt><strong>Purpose:</strong>
    <dd>Writes data to an attribute.
<dt><strong>Description:</strong>
    <dd><code>H5Awrite</code> writes an attribute, specified with 
        <code>attr_id</code>.  The attribute's memory datatype 
        is specified with <code>mem_type_id</code>.  The entire 
        attribute is written from <code>buf</code> to the file. 
<dt><strong>Parameters:</strong>
    <dl>
        <dt><em>hid_t</em> <code>attr_id</code>
            <dd>IN: Identifier of an attribute to write.
        <dt><em>hid_t</em> <code>mem_type_id</code>
            <dd>IN: Identifier of the attribute datatype (in memory).
        <dt><em>void *</em><code>buf</code>
            <dd>IN: Data to be written.
    </dl>
<dt><strong>Returns:</strong>
    <dd>Returns SUCCEED (0) if successful;
        otherwise FAIL (-1).
</dl>


<hr>
<dl>
<dt><strong>Name:</strong> <a name="Annot-Read">H5Aread</a>
<dt><strong>Signature:</strong>
    <dd><em>herr_t</em> <code>H5Aread</code>(<em>hid_t</em> <code>attr_id</code>,
        <em>hid_t</em> <code>mem_type_id</code>,
        <em>void *</em><code>buf</code>
    )
<dt><strong>Purpose:</strong>
    <dd>Reads an attribute.
<dt><strong>Description:</strong>
    <dd><code>H5Aread</code> reads an attribute, specified with 
        <code>attr_id</code>.  The attribute's memory datatype 
        is specified with <code>mem_type_id</code>.  The entire 
        attribute is read into <code>buf</code> from the file. 
<dt><strong>Parameters:</strong>
    <dl>
        <dt><em>hid_t</em> <code>attr_id</code>
            <dd>IN: Identifier of an attribute to read.
        <dt><em>hid_t</em> <code>mem_type_id</code>
            <dd>IN: Identifier of the attribute datatype (in memory).
        <dt><em>void *</em><code>buf</code>
            <dd>IN: Buffer for data to be read.
    </dl>
<dt><strong>Returns:</strong>
    <dd>Returns SUCCEED (0) if successful;
        otherwise FAIL (-1).
</dl>


<hr>
<dl>
<dt><strong>Name:</strong> <a name="Annot-GetSpace">H5Aget_space</a>
<dt><strong>Signature:</strong>
    <dd><em>hid_t</em> <code>H5Aget_space</code>(<em>hid_t</em> <code>attr_id</code>)
<dt><strong>Purpose:</strong>
    <dd>Gets a copy of the dataspace for an attribute.
<dt><strong>Description:</strong>
    <dd><code>H5Aget_space</code> retrieves a copy of the dataspace 
        for an attribute.  The dataspace identifier returned from 
        this function must be released with <code>H5Sclose</code>
        or resource leaks will develop.
<dt><strong>Parameters:</strong>
    <dl>
        <dt><em>hid_t</em> <code>attr_id</code>
            <dd>IN: Identifier of an attribute. 
    </dl>
<dt><strong>Returns:</strong>
    <dd>Returns attribute dataspace identifier if successful;
        otherwise FAIL (-1).
</dl>


<hr>
<dl>
<dt><strong>Name:</strong> <a name="Annot-GetType">H5Aget_type</a>
<dt><strong>Signature:</strong>
    <dd><em>hid_t</em> <code>H5Aget_type</code>(<em>hid_t</em> <code>attr_id</code>)
<dt><strong>Purpose:</strong>
    <dd>Gets an attribute datatype.
<dt><strong>Description:</strong>
    <dd><code>H5Aget_type</code> retrieves a copy of the datatype 
        for an attribute.  
        <p>
        The datatype is reopened if it is a named type before returning
        it to the application.  The datatypes returned by this function
        are always read-only.  If an error occurs when atomizing the 
        return datatype, then the datatype is closed.
        <p>
        The datatype identifier returned from this function must be 
        released with <code>H5Tclose</code> or resource leaks will develop.
<dt><strong>Parameters:</strong>
    <dl>
        <dt><em>hid_t</em> <code>attr_id</code>
            <dd>IN: Identifier of an attribute.
    </dl>
<dt><strong>Returns:</strong>
    <dd>Returns a datatype identifier if successful;
        otherwise FAIL (-1).
</dl>


<hr>
<dl>
<dt><strong>Name:</strong> <a name="Annot-GetName">H5Aget_name</a>
<dt><strong>Signature:</strong>
    <dd><em>size_t</em> <code>H5Aget_name</code>(<em>hid_t</em> <code>attr_id</code>,
        <em>char *</em><code>buf</code>,
        <em>size_t</em> <code>buf_size</code>
    )
<dt><strong>Purpose:</strong>
    <dd>Gets an attribute name.
<dt><strong>Description:</strong>
    <dd><code>H5Aget_name</code> retrieves the name of an attribute 
        specified by the identifier, <code>attr_id</code>.
        Up to <code>buf_size</code> characters are stored in 
        <code>buf</code> followed by a <code>\0</code> string
        terminator.  If the name of the attribute is longer than 
        <code>buf_size</code> -1, the string terminator is stored in the
        last position of the buffer to properly terminate the string.
<dt><strong>Parameters:</strong>
    <dl>
        <dt><em>hid_t</em> <code>attr_id</code>
            <dd>IN: Identifier of the attribute.
        <dt><em>char *</em><code>buf</code>
            <dd>IN: Buffer to store name in.
        <dt><em>size_t</em> <code>buf_size</code>
            <dd>IN: The size of the buffer to store the name in.
    </dl>
<dt><strong>Returns:</strong>
    <dd>Returns the length of the attribute's name, which may be
        longer than <code>buf_size</code>, if successful.
        Otherwise returns FAIL (-1).
</dl>


<hr>
<dl>
<dt><strong>Name:</strong> <a name="Annot-NumAttrs">H5Anum_attrs</a>
<dt><strong>Signature:</strong>
    <dd><em>int</em> <code>H5Anum_attrs</code>(<em>hid_t</em> <code>loc_id</code>)
<dt><strong>Purpose:</strong>
    <dd>Determines the number of attributes attached to an object.
<dt><strong>Description:</strong>
    <dd><code>H5Anum_attrs</code> returns the number of attributes 
        attached to the object specified by its identifier, 
        <code>loc_id</code>.  
        The object can be a group, dataset, or named datatype.
<dt><strong>Parameters:</strong>
    <dl>
        <dt><em>hid_t</em> <code>loc_id</code>
            <dd>IN: Identifier of a group, dataset, or named datatype.
    </dl>
<dt><strong>Returns:</strong>
    <dd>Returns the number of attributes if successful;
        otherwise FAIL (-1).
</dl>


<hr>
<dl>
<dt><strong>Name:</strong> <a name="Annot-Iterate">H5Aiterate</a>
<dt><strong>Signature:</strong>
    <dd><em>int</em> <code>H5Aiterate</code>(<em>hid_t</em> <code>loc_id</code>,
        <em>unsigned *</em> <code>idx</code>,
        <em>H5A_operator_t</em> <code>op</code>,
        <em>void *</em><code>op_data</code>
    )
<dt><strong>Purpose:</strong>
    <dd>Calls a user's function for each attribute on an object.
<dt><strong>Description:</strong>
    <dd><code>H5Aiterate</code> iterates over the attributes of
        the object specified by its identifier, <code>loc_id</code>.
        The object can be a group, dataset, or named datatype.
        For each attribute of the object, the <code>op_data</code>
        and some additional information specified below are passed 
        to the operator function <code>op</code>.
        The iteration begins with the attribute specified by its
        index, <code>idx</code>; the index for the next attribute 
        to be processed by the operator, <code>op</code>, is 
        returned in <code>idx</code>.
        If <code>idx</code> is the null pointer, then all attributes
        are processed.
        <p>
        The prototype for <code>H5A_operator_t</code> is: <br>
            <code>typedef herr_t (*H5A_operator_t)(hid_t <em>loc_id</em>,
                  const char *<em>attr_name</em>, 
                  void *<em>operator_data</em>);
            </code>
        <p>
        The operation receives the identifier for the group, dataset
        or named datatype being iterated over, <code>loc_id</code>, the
        name of the current attribute about the object, <code>attr_name</code>,
        and the pointer to the operator data passed in to <code>H5Aiterate</code>,
        <code>op_data</code>.  The return values from an operator are:
        <ul>
        <li>Zero causes the iterator to continue, returning zero when all 
            attributes 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 attribute.
        <li>Negative causes the iterator to immediately return that value,
            indicating failure.  The iterator can be restarted at the next
            attribute.
        </ul>
<dt><strong>Parameters:</strong>
    <dl>
        <dt><em>hid_t</em> <code>loc_id</code>
            <dd>IN: Identifier of a group, dataset or named datatype.
        <dt><em>unsigned *</em> <code>idx</code>
            <dd>IN/OUT: Starting (IN) and ending (OUT) attribute index.
        <dt><em>H5A_operator_t</em> <code>op</code>
            <dd>IN: User's function to pass each attribute to
        <dt><em>void *</em><code>op_data</code>
            <dd>IN/OUT: User's data to pass through to iterator operator function
    </dl>
<dt><strong>Returns:</strong>
    <dd>If successful, returns the return value of the last operator 
        if it was non-zero, or zero if all attributes were processed.
        Otherwise returns FAIL (-1).
</dl>


<hr>
<dl>
<dt><strong>Name:</strong> <a name="Annot-Delete">H5Adelete</a>
<dt><strong>Signature:</strong>
    <dd><em>herr_t</em> <code>H5Adelete</code>(<em>hid_t</em> <code>loc_id</code>,
        <em>const char *</em><code>name</code>
    )
<dt><strong>Purpose:</strong>
    <dd>Deletes an attribute from a location.
<dt><strong>Description:</strong>
    <dd><code>H5Adelete</code> removes the attribute specified by its  
        name, <code>name</code>, from a dataset, group, or named datatype. 
        This function should not be used when attribute identifiers are 
        open on <code>loc_id</code> as it may cause the internal indexes 
        of the attributes to change and future writes to the open 
        attributes to produce incorrect results. 
<dt><strong>Parameters:</strong>
    <dl>
        <dt><em>hid_t</em> <code>loc_id</code>
            <dd>IN: Identifier of the dataset, group, or named datatype 
                to have the attribute deleted from.
        <dt><em>const char *</em><code>name</code>
            <dd>IN: Name of the attribute to delete.
    </dl>
<dt><strong>Returns:</strong>
    <dd>Returns SUCCEED (0) if successful;
        otherwise FAIL (-1).
</dl>


<hr>
<dl>
<dt><strong>Name:</strong> <a name="Annot-Close">H5Aclose</a>
<dt><strong>Signature:</strong>
    <dd><em>herr_t</em> <code>H5Aclose</code>(<em>hid_t</em> <code>attr_id</code>)
<dt><strong>Purpose:</strong>
    <dd>Closes the specified attribute.
<dt><strong>Description:</strong>
    <dd><code>H5Aclose</code> terminates access to the attribute 
        specified by its identifier, <code>attr_id</code>. 
        Further use of the attribute identifier will result in 
        undefined behavior. 
<dt><strong>Parameters:</strong>
    <dl>
        <dt><em>hid_t</em> <code>attr_id</code>
            <dd>IN: Attribute to release access to.
    </dl>
<dt><strong>Returns:</strong>
    <dd>Returns SUCCEED (0) if successful;
        otherwise FAIL (-1).
</dl>


<hr>
<center>
<a href="RM_H5Front.html">HDF5 Reference Manual</a>&nbsp;
<a href="RM_H5.html">H5</a>&nbsp;&nbsp;
H5A&nbsp;&nbsp;
<a href="RM_H5D.html">H5D</a>&nbsp;&nbsp;
<a href="RM_H5E.html">H5E</a>&nbsp;&nbsp;
<a href="RM_H5F.html">H5F</a>&nbsp;&nbsp;
<a href="RM_H5G.html">H5G</a>&nbsp;&nbsp;
<a href="RM_H5P.html">H5P</a>&nbsp;&nbsp;
<a href="RM_H5S.html">H5S</a>&nbsp;&nbsp;
<a href="RM_H5T.html">H5T</a>&nbsp;&nbsp;
<a href="RM_H5Z.html">H5Z</a>&nbsp;&nbsp;
<a href="Glossary.html">Glossary</a>
</center>
<hr>

<address>
<a href="mailto:hdfhelp@ncsa.uiuc.edu">HDF Help Desk</a> 

<br>
Last modified:  14 July 1998

</body>
</html>