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<html>
<head><title>
HDF5/H5I API Specification
</title>
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<h1>H5I: Identifier Interface</h1>
</center>
<h2>Identifier API Functions</h2>
These functions provides tools for working with object identifiers and
object names.
<p>
<strong>The C Interface:</strong>
<table border=0>
<tr><td valign=top>
<ul>
<li><a href="#Identify-IncRef">H5Iinc_ref</a>
<li><a href="#Identify-GetName">H5Iget_name</a>
</ul>
</td><td> </td><td valign=top>
<ul>
<li><a href="#Identify-DecRef">H5Idec_ref</a>
<li><a href="#Identify-GetType">H5Iget_type</a>
</ul>
</td><td> </td><td valign=top>
<ul>
<li><a href="#Identify-GetRef">H5Iget_ref</a>
</ul>
</td></tr>
</table>
<br>
<i>Alphabetical Listing</i>
<table border="0">
<tr>
<td valign="top">
<ul>
<li><a href="#Identify-DecRef">H5Idec_ref</a>
<li><a href="#Identify-GetName">H5Iget_name</a>
</ul>
</td>
<td> </td>
<td valign="top">
<ul>
<li><a href="#Identify-GetRef">H5Iget_ref</a>
<li><a href="#Identify-GetType">H5Iget_type</a>
</ul>
</td>
<td> </td>
<td valign="top">
<ul>
<li><a href="#Identify-IncRef">H5Iinc_ref</a>
</ul>
</td>
</tr>
</table>
<br>
<strong>The FORTRAN90 Interfaces:</strong>
<br>
In general, each FORTRAN90 subroutine performs exactly the same task
as the corresponding C function.
<br>
<table border=0>
<tr><td valign=top>
<ul>
<li><a href="#Identify-IncRef">h5iinc_ref_f</a>
<li><a href="#Identify-GetName">h5iget_name_f</a>
</ul>
</td><td> </td><td valign=top>
<ul>
<li><a href="#Identify-DecRef">h5idec_ref_f</a>
<li><a href="#Identify-GetType">h5iget_type_f</a>
</ul>
</td><td> </td><td valign=top>
<ul>
<li><a href="#Identify-GetRef">h5iget_ref_f</a>
</ul>
</td></tr>
</table>
<!-- NEW PAGE -->
<!-- NEW PAGE -->
<!-- HEADER RIGHT "H5Idec_ref" -->
<hr>
<dl>
<dt><strong>Name:</strong> <a name="Identify-DecRef">H5Idec_ref</a>
<dt><strong>Signature:</strong>
<dd><em>int</em> <code>H5Idec_ref</code>(<em>hid_t</em> <code>obj_id</code>)
<dt><strong>Purpose:</strong>
<dd>Decrements the reference count for an object.
<dt><strong>Description:</strong>
<dd><code>H5Idec_ref</code> decrements the reference count of the object
identified by <code>obj_id</code>.
<p>
The reference count for an object ID is attached to the information
about an object in memory and has no relation to the number of links to
an object on disk.
<p>
The reference count for a newly created object will be 1.
Reference counts for objects may be explicitly modified with this
function or with <code>H5Iinc_ref</code>.
When an object ID's reference count reaches zero, the object will be
closed.
Calling an object ID's 'close' function decrements the reference count
for the ID which normally closes the object, but
if the reference count for the ID has been incremented with
<code>H5Iinc_ref</code>, the object will only be closed when the
reference count
reaches zero with further calls to this function or the
object ID's 'close' function.
<p>
If the object ID was created by a collective parallel call (such as
<code>H5Dcreate</code>, <code>H5Gopen</code>, etc.), the reference
count should be modified by all the processes which have copies of
the ID. Generally this means that group, dataset, attribute, file
and named datatype IDs should be modified by all the processes and
that all other types of IDs are safe to modify by individual processes.
<p>
This function is of particular value when an application is maintaining
multiple copies of an object ID. The object ID can be incremented when
a copy is made. Each copy of the ID can then be safely closed or
decremented and the HDF5 object will be closed when the reference count
for that that object drops to zero.
<dt><strong>Parameters:</strong>
<ul><table>
<tr>
<td valign="top"><em>hid_t</em> <code>obj_id </code></td>
<td valign="top">IN: Object identifier whose reference count will be modified.</td></tr>
</table></ul>
<dt><strong>Returns:</strong>
<dd>Returns a non-negative reference count of the object ID after
decrementing it if successful; otherwise a negative value is returned.
<dt><strong>Fortran90 Interface:</strong> h5idec_ref_f
<dd>
<pre>
SUBROUTINE h5idec_ref_f(obj_id, ref_count, hdferr)
IMPLICIT NONE
INTEGER(HID_T), INTENT(IN) :: obj_id !Object identifier
INTEGER, INTENT(OUT) :: ref_count !Reference count of object ID
INTEGER, INTENT(OUT) :: hdferr ! Error code
! 0 on success, and -1 on failure
END SUBROUTINE h5idec_ref_f
</pre>
<!--<dt><strong>Non-C API(s):</strong>
<dd>
<img src="Graphics/Java.gif">
<img src="Graphics/C++.gif">
-->
</dl>
<!-- NEW PAGE -->
<!-- HEADER RIGHT "H5Iget_name" -->
<hr>
<dl>
<dt><strong>Name:</strong> <a name="Identify-GetName">H5Iget_name</a>
<dt><strong>Signature:</strong>
<dd><em>ssize_t</em> <code>H5Iget_name</code>(<em>hid_t</em> <code>obj_id</code>,
<em>char *</em><code>name</code>,
<em>size_t</em> <code>size</code>
)
<dt><strong>Purpose:</strong> </dt>
<dd>Retrieves a name of an object based on the object identifier.
<dt><strong>Description:</strong>
<dd><code>H5Iget_name</code> retrieves a name for the object identified
by <code>obj_id</code>.
<p>
Up to <code>size</code> characters of the name are returned in
<code>name</code>; additional characters, if any, are not returned
to the user application.
<p>
If the length of the name, which determines the required
value of <code>size</code>, is unknown, a preliminary
<code>H5Iget_name</code> call can be made.
The return value of this call will be the size of the
object name.
That value can then be assigned to <code>size</code>
for a second <code>H5Iget_name</code> call,
which will retrieve the actual name.
<p>
If there is no name associated with the object identifier
or if the name is <code>NULL</code>, <code>H5Iget_name</code>
returns <code>0</code> (zero).
<p>
Note that an object in an HDF5 file may have multiple names,
varying according to the path through the HDF5 group
hierarchy used to reach that object.
<dt><strong>Parameters:</strong>
<ul><table>
<tr>
<td valign="top"><em>hid_t</em> <code>obj_id </code></td>
<td valign="top">IN: Identifier of the object.
This identifier can refer to a group, dataset, or named datatype.</td></tr>
<tr>
<td valign="top"><em>char *</em><code>name</code></td>
<td valign="top">OUT: A name associated with the identifier.</td></tr>
<tr>
<td valign="top"><em>size_t size</em></td>
<td valign="top">IN: The size of the <code>name</code> buffer.</td></tr>
</table></ul>
<dt><strong>Returns:</strong>
<dd>Returns the length of the name if successful,
returning <code>0</code> (zero) if no name is associated with the identifier.
Otherwise returns a negative value.
<dt><strong>Fortran90 Interface:</strong> h5iget_name_f
<dd>
<pre>
SUBROUTINE h5iget_name_f(obj_id, buf, buf_size, hdferr)
IMPLICIT NONE
INTEGER(HID_T), INTENT(IN) :: obj_id ! Object identifier
CHARACTER(LEN=*), INTENT(OUT) :: buf ! Buffer to hold object name
INTEGER(SIZE_T), INTENT(IN) :: buf_size ! Buffer size
INTEGER(SIZE_T), INTENT(OUT) :: name_size ! Name size
INTEGER, INTENT(OUT) :: hdferr ! Error code
! 0 on success, and -1 on failure
END SUBROUTINE h5iget_name_f
</pre>
<!--<dt><strong>Non-C API(s):</strong>
<dd>
<img src="Graphics/Java.gif">
<img src="Graphics/C++.gif">
-->
</dl>
<!-- NEW PAGE -->
<!-- HEADER RIGHT "H5Iget_ref" -->
<hr>
<dl>
<dt><strong>Name:</strong> <a name="Identify-GetRef">H5Iget_ref</a>
<dt><strong>Signature:</strong>
<dd><em>int</em> <code>H5Iget_ref</code>(<em>hid_t</em> <code>obj_id</code>)
<dt><strong>Purpose:</strong>
<dd>Retrieves the reference count for an object.
<dt><strong>Description:</strong>
<dd><code>H5Iget_ref</code> retrieves the reference count of the object
identified by <code>obj_id</code>.
<p>
The reference count for an object ID is attached to the information
about an object in memory and has no relation to the number of links to
an object on disk.
<p>
This function can also be used to check if an object ID is still valid.
A non-negative return value from this function indicates that the ID
is still valid.
<dt><strong>Parameters:</strong>
<ul><table>
<tr>
<td valign="top"><em>hid_t</em> <code>obj_id </code></td>
<td valign="top">IN: Object identifier whose reference count will be retrieved.</td></tr>
</table></ul>
<dt><strong>Returns:</strong>
<dd>Returns a non-negative current reference count of the object ID
if successful; otherwise a negative value is returned.
<dt><strong>Fortran90 Interface:</strong> h5iget_ref_f
<dd>
<pre>
SUBROUTINE h5iget_ref_f(obj_id, ref_count, hdferr)
IMPLICIT NONE
INTEGER(HID_T), INTENT(IN) :: obj_id !Object identifier
INTEGER, INTENT(OUT) :: ref_count !Reference count of object ID
INTEGER, INTENT(OUT) :: hdferr ! Error code
! 0 on success, and -1 on failure
END SUBROUTINE h5iget_ref_f
</pre>
<!--<dt><strong>Non-C API(s):</strong>
<dd>
<img src="Graphics/Java.gif">
<img src="Graphics/C++.gif">
-->
</dl>
<!-- NEW PAGE -->
<!-- HEADER RIGHT "H5Iget_type" -->
<hr>
<dl>
<dt><strong>Name:</strong> <a name="Identify-GetType">H5Iget_type</a>
<dt><strong>Signature:</strong>
<dd><em>H5I_type_t</em> <code>H5Iget_type</code>(<em>hid_t</em> <code>obj_id</code>)
<dt><strong>Purpose:</strong>
<dd>Retrieves the type of an object.
<dt><strong>Description:</strong>
<dd><code>H5Iget_type</code> retrieves the type of the object
identified by <code>obj_id</code>.
<p>
Valid types returned by the function are
<table>
<tr><td width=200><code> H5I_FILE</code>
</td><td>File</td></tr>
<tr><td><code> H5I_GROUP</code>
</td><td>Group</td></tr>
<tr><td><code> H5I_DATATYPE</code>
</td><td>Datatype</td></tr>
<tr><td><code> H5I_DATASPACE</code>
</td><td>Dataspace</td></tr>
<tr><td><code> H5I_DATASET</code>
</td><td>Dataset</td></tr>
<tr><td><code> H5I_ATTR</code>
</td><td>Attribute</td></tr>
</table>
If no valid type can be determined or the identifier
submitted is invalid, the function returns
<table>
<tr><td width=200><code> H5I_BADID</code>
</td><td>Invalid identifier</td></tr>
</table>
<p>
This function is of particular value in determining the
type of object closing function (<code>H5Dclose</code>,
<code>H5Gclose</code>, etc.) to call after a call to
<code>H5Rdereference</code>.
<dt><strong>Parameters:</strong>
<ul><table>
<tr>
<td valign="top"><em>hid_t</em> <code>obj_id </code></td>
<td valign="top">IN: Object identifier whose type is to be determined.</td></tr>
</table></ul>
<dt><strong>Returns:</strong>
<dd>Returns the object type if successful;
otherwise <code>H5I_BADID</code>.
<dt><strong>Fortran90 Interface:</strong> h5iget_type_f
<dd>
<pre>
SUBROUTINE h5iget_type_f(obj_id, type, hdferr)
IMPLICIT NONE
INTEGER(HID_T), INTENT(IN) :: obj_id !Object identifier
INTEGER, INTENT(OUT) :: type !type of an object.
!possible values are:
!H5I_FILE_F(1)
!H5I_GROUP_F(2)
!H5I_DATATYPE_F(3)
!H5I_DATASPACE_F(4)
!H5I_DATASET_F(5)
!H5I_ATTR_F(6)
!H5I_BADID_F(-1)
INTEGER, INTENT(OUT) :: hdferr ! E rror code
! 0 on success, and -1 on failure
END SUBROUTINE h5iget_type_f
</pre>
<!--<dt><strong>Non-C API(s):</strong>
<dd>
<img src="Graphics/Java.gif">
<img src="Graphics/C++.gif">
-->
</dl>
<!-- NEW PAGE -->
<!-- HEADER RIGHT "H5Iinc_ref" -->
<hr>
<dl>
<dt><strong>Name:</strong> <a name="Identify-IncRef">H5Iinc_ref</a>
<dt><strong>Signature:</strong>
<dd><em>int</em> <code>H5Iinc_ref</code>(<em>hid_t</em> <code>obj_id</code>)
<dt><strong>Purpose:</strong>
<dd>Increments the reference count for an object.
<dt><strong>Description:</strong>
<dd><code>H5Iinc_ref</code> increments the reference count of the object
identified by <code>obj_id</code>.
<p>
The reference count for an object ID is attached to the information
about an object in memory and has no relation to the number of links to
an object on disk.
<p>
The reference count for a newly created object will be 1.
Reference counts for objects may be explicitly modified with this
function or with <code>H5Idec_ref</code>.
When an object ID's reference count reaches zero, the object will be
closed.
Calling an object ID's 'close' function decrements the reference count
for the ID which normally closes the object, but
if the reference count for the ID has been incremented with this
function, the object will only be closed when the reference count
reaches zero with further calls to <code>H5Idec_ref</code> or the
object ID's 'close' function.
<p>
If the object ID was created by a collective parallel call (such as
<code>H5Dcreate</code>, <code>H5Gopen</code>, etc.), the reference
count should be modified by all the processes which have copies of
the ID. Generally this means that group, dataset, attribute, file
and named datatype IDs should be modified by all the processes and
that all other types of IDs are safe to modify by individual processes.
<p>
This function is of particular value when an application is maintaining
multiple copies of an object ID. The object ID can be incremented when
a copy is made. Each copy of the ID can then be safely closed or
decremented and the HDF5 object will be closed when the reference count
for that that object drops to zero.
<dt><strong>Parameters:</strong>
<ul><table>
<tr>
<td valign="top"><em>hid_t</em> <code>obj_id </code></td>
<td valign="top">IN: Object identifier whose reference count will be modified.</td></tr>
</table></ul>
<dt><strong>Returns:</strong>
<dd>Returns a non-negative reference count of the object ID after
incrementing it if successful; otherwise a negative value is returned.
<dt><strong>Fortran90 Interface:</strong> h5iinc_ref_f
<dd>
<pre>
SUBROUTINE h5iinc_ref_f(obj_id, ref_count, hdferr)
IMPLICIT NONE
INTEGER(HID_T), INTENT(IN) :: obj_id !Object identifier
INTEGER, INTENT(OUT) :: ref_count !Reference count of object ID
INTEGER, INTENT(OUT) :: hdferr ! Error code
! 0 on success, and -1 on failure
END SUBROUTINE h5iinc_ref_f
</pre>
<!--<dt><strong>Non-C API(s):</strong>
<dd>
<img src="Graphics/Java.gif">
<img src="Graphics/C++.gif">
-->
</dl>
<!-- #BeginLibraryItem "/ed_libs/NavBar_RM.lbi" --><hr>
<center>
<table border=0 width=98%>
<tr><td valign=top align=left>
<a href="index.html">HDF5 documents and links</a> <br>
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<a href="mailto:hdfhelp@ncsa.uiuc.edu">HDF Help Desk</a>
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Describes HDF5 Release 1.7, the unreleased development branch; working toward HDF5 Release 1.8.0
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