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
|
<HTML><HEAD>
<TITLE>HDF5 Tutorial - Iterating over Group Members
</TITLE>
</HEAD>
<body bgcolor="#ffffff">
<!-- BEGIN MAIN BODY -->
<A HREF="http://www.ncsa.uiuc.edu/"><img border=0
src="http://www.ncsa.uiuc.edu/Images/NCSAhome/footerlogo.gif"
width=78 height=27 alt="NCSA"><P></A>
[ <A HREF="title.html"><I>HDF5 Tutorial Top</I></A> ]
<H1>
<BIG><BIG><BIG><FONT COLOR="#c101cd">Iterating over Group Members</FONT>
</BIG></BIG></BIG></H1>
<hr noshade size=1>
<BODY>
<H2>Contents:</H2>
<UL>
<LI><A HREF="#def">How to Iterate Over Group Members</A>
<LI>Programming Example
<UL>
<LI> <A HREF="#desc">Description</A>
<LI> <A HREF="#rem">Remarks</A>
<!--
<LI> <A HREF="#fc">File Contents</A>
<LI> <A HREF="#ddl">Dataset Definition in DDL</A>
-->
</UL>
</UL>
<HR>
<A NAME="def">
<H2>How to Iterate Over Group Members</H2>
This section discusses how to find names and object types of HDF5 group
members.
<P>
The HDF5 Group interface has a function, H5Giterate, to iterate over the
group members.
<P>
Operations on each group member can be performed during the iteration process.
The operator function and its data are passed to the iterator as parameters.
There are no restrictions on what kind of operations can be performed on
group members during the iteration procedure.
<P>
The following steps are involved:
<OL>
<LI> Write an operator function which will be used during the iteration process.
The HDF5 library defines the operator function signature and return values.
<LI> Open the group to iterate through.
<LI> Use H5Giterate to iterate through the group or just a few members of
the group.
</OL>
<H2> Programming Example</H2>
<A NAME="desc">
<H3><U>Description</U></H3>
In this example we iterate through the members of the root group. The
operator function displays the members' names and their object types.
The object type can be a group, dataset, or named datatype.
[ <A HREF="examples/h5_iterate.c">Download h5_iterate.c</A> ]
<PRE>
++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
#include <hdf5.h>
#define FILE "iterate.h5"
#define FALSE 0
/* 1-D dataset with fixed dimensions */
#define SPACE1_NAME "Space1"
#define SPACE1_RANK 1
#define SPACE1_DIM1 4
herr_t file_info(hid_t loc_id, const char *name, void *opdata);
/* Operator function */
int
main(void) {
hid_t file; /* HDF5 File IDs */
hid_t dataset; /* Dataset ID */
hid_t group; /* Group ID */
hid_t sid; /* Dataspace ID */
hid_t tid; /* Datatype ID */
hsize_t dims[] = {SPACE1_DIM1};
herr_t ret; /* Generic return value */
/* Compound datatype */
typedef struct s1_t {
unsigned int a;
unsigned int b;
float c;
} s1_t;
/* Create file */
file = H5Fcreate(FILE, H5F_ACC_TRUNC, H5P_DEFAULT, H5P_DEFAULT);
/* Create dataspace for datasets */
sid = H5Screate_simple(SPACE1_RANK, dims, NULL);
/* Create a group */
group=H5Gcreate(file,"Group1",-1);
/* Close a group */
ret = H5Gclose(group);
/* Create a dataset */
dataset=H5Dcreate(file,"Dataset1",H5T_STD_U32LE,sid,H5P_DEFAULT);
/* Close Dataset */
ret = H5Dclose(dataset);
/* Create a datatype */
tid = H5Tcreate (H5T_COMPOUND, sizeof(s1_t));
/* Insert fields */
ret=H5Tinsert (tid, "a", HOFFSET(s1_t,a), H5T_NATIVE_INT);
ret=H5Tinsert (tid, "b", HOFFSET(s1_t,b), H5T_NATIVE_INT);
ret=H5Tinsert (tid, "c", HOFFSET(s1_t,c), H5T_NATIVE_FLOAT);
/* Save datatype for later */
ret=H5Tcommit (file, "Datatype1", tid);
/* Close datatype */
ret = H5Tclose(tid);
/* Iterate through the file to see members of the root group */
printf(" Objects in the root group are:\n");
printf("\n");
H5Giterate(file, "/", NULL, file_info, NULL);
/* Close file */
ret = H5Fclose(file);
return 0;
}
/*
* Operator function.
*/
herr_t file_info(hid_t loc_id, const char *name, void *opdata)
{
H5G_stat_t statbuf;
/*
* Get type of the object and display its name and type.
* The name of the object is passed to this function by
* the Library. Some magic :-)
*/
H5Gget_objinfo(loc_id, name, FALSE, &statbuf);
switch (statbuf.type) {
case H5G_GROUP:
printf(" Object with name %s is a group \n", name);
break;
case H5G_DATASET:
printf(" Object with name %s is a dataset \n", name);
break;
case H5G_TYPE:
printf(" Object with name %s is a named datatype \n", name);
break;
default:
printf(" Unable to identify an object ");
}
return 0;
}
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
</PRE>
The output of this program is:
<PRE>
Objects in the root group are:
Object with name Dataset1 is a dataset
Object with name Datatype1 is a named datatype
Object with name Group1 is a group
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
</PRE>
<A NAME="rem">
<H3><U>Remarks</U></H3>
<P>
<UL>
<LI> The operator function in this example is called <I>file_info</I>.
The signature of the operator function is as follows:
<PRE>
herr_t *(H5G_operator_t) (hid_group_id, const char* name, void *operator_data)
</PRE>
<UL>
<LI>The first parameter is a group identifier for the group being iterated
over. It is passed to the operator by the iterator function, H5Giterate.
<LI> The second parameter is the name of the current object. The name is
passed to the operator function by the HDF5 library.
<LI> The third parameter is the operator data. It is passed to and from
the operator by the iterator, H5Giterate.
The operator function in this example just prints the name and type
of the current object and then exits.
This information can also be used to open the object and perform
different operations or queries. For example a named datatype object's
name can be used to open the datatype and query its properties.
</UL>
<P>
The operator return value defines the behavior of the iterator.
<UL>
<LI>A zero return value causes the iterator to continue, returning
zero when all group members have been processed.
<LI>A positive value causes the iterator to immediately return that
value, indicating a short-circuit success. The iterator can be restarted
at the next group member.
<LI>A negative value causes the iterator to immediately return that value,
indicating failure. The iterator can be restarted at the next group
member.
</UL>
<P>
In this example the operator function returns 0, which causes the iterator
to continue and go through all group members.
<P>
<LI>The function H5Gget_objinfo is used to determine the type of the object.
It also returns the modification time, number of hard links, and some
other information.
<P>
The signature of this function is as follows:
<PRE>
herr_t H5Gget_objinfo(hid_t loc_id, const char * name, hbool_t follow_link,
H5G_stat_t *statbuf)
</PRE>
<UL>
<LI> The first two arguments specify the object by its location and name.
This example uses the group identifier and name relative to the group
to specify the object.
<LI> The third argument is a flag which indicates whether a
symbolic link should be followed or not. A zero value indicates
that information should be returned for the link itself, but not
about the object it points to.
The root group in this example does not have objects that are
links, so this flag is not important for our example.
<LI> The fourth argument is a buffer to return information in.
Type information is returned into the field "type" of the
H5G_stat_t data structure (statbuf.type). Possible values are:
H5G_GROUP, H5G_DATASET, H5G_TYPE, and H5G_LINK.
</UL>
<P>
<LI> The H5Giterate function has the following signature:
<PRE>
int H5Giterate(hid_t loc_id, const char *name , idx,
H5G_operator_t operator, void * operator_data)
</PRE>
<UL>
<LI> The first parameter is the group for the group being iterated over.
<LI> The second parameter is the group name.
<LI> The third parameter specifies that iteration begins with the
<I>idx</I> object in the group and the next element to be processed
is returned in the <I>idx</I> parameter. In our example NULL is
used to start 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 a non-zero value.
<LI> The fourth parameter is an operator function.
<LI> The fifth argument is the operator data. We used NULL since no
data was passed to and from the operator.
</UL>
</UL>
<!--
<A NAME="fc">
<H3><U>File Contents</U></H3>
-->
<!-- BEGIN FOOTER INFO -->
<P><hr noshade size=1>
<font face="arial,helvetica" size="-1">
<a href="http://www.ncsa.uiuc.edu/"><img border=0
src="http://www.ncsa.uiuc.edu/Images/NCSAhome/footerlogo.gif"
width=78 height=27 alt="NCSA"><br>
The National Center for Supercomputing Applications</A><br>
<a href="http://www.uiuc.edu/">University of Illinois
at Urbana-Champaign</a><br>
<br>
<!-- <A HREF="helpdesk.mail.html"> -->
<A HREF="mailto:hdfhelp@ncsa.uiuc.edu">
hdfhelp@ncsa.uiuc.edu</A>
<BR> <H6>Last Modified: August 27, 1999</H6><BR>
<!-- modified by Barbara Jones - bljones@ncsa.uiuc.edu -->
</FONT>
<BR>
<!-- <A HREF="mailto:hdfhelp@ncsa.uiuc.edu"> -->
</BODY>
</HTML>
|
