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<html>
<head><title>
HDF5/H5I API Specification
</title>

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<hr>
<!-- #EndLibraryItem --><center>
<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-GetName">H5Iget_name</a>
    <li><a href="#Identify-GetType">H5Iget_type</a>
</ul>
</td><td>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</td><td valign=top>
<ul>
    <li><a href="#Identify-GetFileId">H5Iget_file_id</a>
    <li><a href="#Identify-GetRef">H5Iget_ref</a>
</ul>
</td><td>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</td><td valign=top>
<ul>
    <li><a href="#Identify-IncRef">H5Iinc_ref</a>
    <li><a href="#Identify-DecRef">H5Idec_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-GetFileId">H5Iget_file_id</a>
	</ul>     
    </td>
    
    <td>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</td>
    
    <td valign="top">
	<ul>
            <li><a href="#Identify-GetName">H5Iget_name</a>
            <li><a href="#Identify-GetRef">H5Iget_ref</a>
	</ul>
    </td>
    
    <td>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</td>
    
    <td valign="top">
	<ul>
            <li><a href="#Identify-GetType">H5Iget_type</a>
            <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-GetName">h5iget_name_f</a>
    <li><a href="#Identify-GetType">h5iget_type_f</a>
</ul>
</td><td>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</td><td valign=top>
<ul>
    <li><a href="#Identify-GetFileId">H5Iget_file_id</a>
    <li><a href="#Identify-GetRef">h5iget_ref_f</a>
</ul>
</td><td>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</td><td valign=top>
<ul>
    <li><a href="#Identify-IncRef">h5iinc_ref_f</a>
    <li><a href="#Identify-DecRef">h5idec_ref_f</a>
</ul>
</td></tr>
</table>

<!-- NEW PAGE -->
<!-- HEADER RIGHT " " -->
<!-- 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>&nbsp;<code>obj_id&nbsp;&nbsp;&nbsp;&nbsp;</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">
        -->
<dt><strong>History:</strong>
	<ul><table width="90%">
        <tr>
		  <td valign="top" align="left" width="10%">
		    <strong>Release</strong>&nbsp;&nbsp;&nbsp;&nbsp;</td>
          <td valign="top" align="left">
		    <strong>C</strong></td>
		  <td valign="top" align="left">
		    &nbsp;&nbsp;&nbsp;&nbsp;</td>
		  <td valign="top" align="left">
		    <strong>Fortran90</strong></td></tr>
        <tr>
		  <td valign="top">1.6.2</td>
          <td valign="top">
		    Function introduced in this release.</td>
		  <td valign="top">&nbsp;</td>
		  <td valign="top">
		    Fortran subroutine introduced in this 
			release.</td></tr>
    </table></ul>
</dl>


<!-- NEW PAGE -->
<!-- HEADER RIGHT "H5Iget_file_id" -->
<hr>
<dl>
<dt><strong>Name:</strong> <a name="Identify-GetFileId">H5Iget_file_id</a>
<dt><strong>Signature:</strong>
    <dd><em>hid_t</em> <code>H5Iget_file_id</code>(<em>hid_t</em> <code>obj_id</code>)
<dt><strong>Purpose:</strong>
    <dd>Retrieves an identifier for the file containing the specified object.
<dt><strong>Description:</strong>
    <dd><code>H5Iget_file_id</code> returns the identifier of the file 
        associated with the object referenced by <code>obj_id</code>.  
        <p>
        <code>obj_id</code> can be a file, group, dataset, named datatype, 
        or attribute identifier.
        <p>
        Note that the HDF5 Library permits an application to close a file
        while objects within the file remain open.
        If the file containing the object <code>obj_id</code> 
        is still open, <code>H5Iget_file_id</code> will retrieve the 
        existing file identifier.
        If there is no existing file identifier for the file, 
        i.e., the file has been closed, 
        <code>H5Iget_file_id</code> will reopen the file and 
        return a new file identifier.
        In either case, the file identifier must eventually be released 
        using <code>H5Fclose</code>.  
<dt><strong>Parameters:</strong>
    <ul>
    <table>
      <tr>
        <td valign="top"><em>hid_t</em>&nbsp;<code>obj_id&nbsp;&nbsp;&nbsp;&nbsp;</code></td>
        <td valign="top">IN: Identifier of the object whose associated 
            file identifier will be returned.</td>
      </tr>
    </table>
    </ul>
<dt><strong>Returns:</strong>
    <dd>Returns a file identifier on success, negative on failure.
<dt><strong>Fortran90 Interface:</strong>
    <dd>
    <pre>
SUBROUTINE h5iget_file_id_f(obj_id, file_id, hdferr) 

  IMPLICIT NONE
  INTEGER(HID_T), INTENT(IN)  :: obj_id     ! Object identifier 
  INTEGER(HID_T), INTENT(OUT) :: file_id    ! File identifier
  INTEGER, INTENT(OUT) :: hdferr            ! Error code

END SUBROUTINE h5iget_file_id_f
    </pre>

<!--<dt><strong>Non-C API(s):</strong>
    <dd>
        <img src="Graphics/Java.gif">
        <img src="Graphics/C++.gif">
        -->
<dt><strong>History:</strong>
	<ul><table width="90%">
        <tr>
		  <td valign="top" align="left" width="10%">
		    <strong>Release</strong>&nbsp;&nbsp;&nbsp;&nbsp;</td>
          <td valign="top" align="left">
		    <strong>C</strong></td>
		  <td valign="top" align="left">
		    &nbsp;&nbsp;&nbsp;&nbsp;</td>
		  <td valign="top" align="left">
		    <strong>Fortran90</strong></td></tr>
        <tr>
		  <td valign="top">1.6.3</td>
          <td valign="top">
		    Function introduced in this release.</td>
		  <td valign="top">&nbsp;</td>
		  <td valign="top">
		    Fortran subroutine introduced in this 
			release.</td></tr>
    </table></ul>
</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 the object identified by <code>obj_id</code> is an attribute,
        as determined via 
        <a href="#Identify-GetType"><code>H5Iget_type</code></a>,
        <code>H5Iget_name</code> retrieves the name of the object 
        to which that attribute is attached. 
        To retrieve the name of the attribute itself, use
        <a href="RM_H5A.html#Annot-GetName"><code>H5Aget_name</code></a>.
        <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>&nbsp;<code>obj_id&nbsp;&nbsp;&nbsp;&nbsp;</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">
        -->
<dt><strong>History:</strong>
    <ul><table width="90%">
        <tr>
		  <td valign="top" align="left" width="10%">
		    <strong>Release</strong>&nbsp;&nbsp;&nbsp;&nbsp;</td>
          <td valign="top" align="left">
		    <strong>C</strong></td></tr>
        <tr>
		  <td valign="top">1.6.0</td>
          <td valign="top">
		    Function introduced in this release.</td></tr>
    </table></ul>
</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>&nbsp;<code>obj_id&nbsp;&nbsp;&nbsp;&nbsp;</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">
        -->
<dt><strong>History:</strong>
	<ul><table width="90%">
        <tr>
		  <td valign="top" align="left" width="10%">
		    <strong>Release</strong>&nbsp;&nbsp;&nbsp;&nbsp;</td>
          <td valign="top" align="left">
		    <strong>C</strong></td>
		  <td valign="top" align="left">
		    &nbsp;&nbsp;&nbsp;&nbsp;</td>
		  <td valign="top" align="left">
		    <strong>Fortran90</strong></td></tr>
        <tr>
		  <td valign="top">1.6.2</td>
          <td valign="top">
		    Function introduced in this release.</td>
		  <td valign="top">&nbsp;</td>
		  <td valign="top">
		    Fortran subroutine introduced in this 
			release.</td></tr>
    </table></ul>
</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>&nbsp;&nbsp;&nbsp;&nbsp;H5I_FILE</code>
           </td><td>File</td></tr>
        <tr><td><code>&nbsp;&nbsp;&nbsp;&nbsp;H5I_GROUP</code>
           </td><td>Group</td></tr>
        <tr><td><code>&nbsp;&nbsp;&nbsp;&nbsp;H5I_DATATYPE</code>
           </td><td>Datatype</td></tr>
        <tr><td><code>&nbsp;&nbsp;&nbsp;&nbsp;H5I_DATASPACE</code>
           </td><td>Dataspace</td></tr>
        <tr><td><code>&nbsp;&nbsp;&nbsp;&nbsp;H5I_DATASET</code>
           </td><td>Dataset</td></tr>
        <tr><td><code>&nbsp;&nbsp;&nbsp;&nbsp;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>&nbsp;&nbsp;&nbsp;&nbsp;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>&nbsp;<code>obj_id&nbsp;&nbsp;&nbsp;&nbsp;</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
                                        !H5I_GROUP_F
                                        !H5I_DATATYPE_F
                                        !H5I_DATASPACE_F
                                        !H5I_DATASET_F
                                        !H5I_ATTR_F
                                        !H5I_BADID_F
  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>&nbsp;<code>obj_id&nbsp;&nbsp;&nbsp;&nbsp;</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">
        -->
<dt><strong>History:</strong>
	<ul><table width="90%">
        <tr>
		  <td valign="top" align="left" width="10%">
		    <strong>Release</strong>&nbsp;&nbsp;&nbsp;&nbsp;</td>
          <td valign="top" align="left">
		    <strong>C</strong></td>
		  <td valign="top" align="left">
		    &nbsp;&nbsp;&nbsp;&nbsp;</td>
		  <td valign="top" align="left">
		    <strong>Fortran90</strong></td></tr>
        <tr>
		  <td valign="top">1.6.2</td>
          <td valign="top">
		    Function introduced in this release.</td>
		  <td valign="top">&nbsp;</td>
		  <td valign="top">
		    Fortran subroutine introduced in this 
			release.</td></tr>
    </table></ul>
</dl>

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<a href="mailto:hdfhelp@ncsa.uiuc.edu">HDF Help Desk</a> 
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Describes HDF5 Release 1.6.5, October 2005
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