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<html>
<head><title>
HDF5/H5R API Specification
</title>

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<h1>H5R: Reference Interface</h1>
</center>

<h2>Reference API Functions</h2>

The Reference interface allows the user to create references 
to specific objects and data regions in an HDF5 file.

<p>
<strong>The C Interfaces:</strong>

<table border=0 width=80%>
<tr><td valign=top width=40%>
<ul>
    <li><a href="#Reference-Create">H5Rcreate</a>
    <li><a href="#Reference-Dereference">H5Rdereference</a>
</ul>
</td><td valign=top width=40%>
<ul>
    <li><a href="#Reference-GetRegion">H5Rget_region</a>
    <li><a href="#Reference-GetObjType">H5Rget_obj_type</a>
    <li><span class="1_4_compat"><a href="#Reference-GetObjectType">H5Rget_object_type</a></span> *
</ul>
</td><td valign=top width=20%>
<ul>
    &nbsp;
</ul>
</td></tr>
</table>

* Functions labelled with an asterisk (*) are provided only for 
backwards compatibility with HDF5 Releases 1.4.<i>x</i>.  
See further notes in the description of each function.
<p>

<i>Alphabetical Listing</i>

<table border="0">
  <tr>
    <td valign="top">
      <li><a href="#Reference-Create">H5Rcreate</a>
      <li><a href="#Reference-Dereference">H5Rdereference</a>      
    </td>
    
    <td>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</td>
    
    <td valign="top">
      <li><a href="#Reference-GetObjType">H5Rget_obj_type</a>
      <li><a href="#Reference-GetObjectType">H5Rget_object_type</a> *
    </td>
    
    <td>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</td>
    
    <td valign="top">
      <li><a href="#Reference-GetRegion">H5Rget_region</a>
    </td>
  </tr>
</table>

<p>
<strong>The FORTRAN90 Interfaces:</strong>

<br>
<font size=-1>
<i>In general, each FORTRAN90 subroutine performs exactly the same task 
as the corresponding C function.  The links below go to the C function 
descriptions, which serve as general descriptions for both.  A button, 
under <strong>Non-C API(s)</strong> at the end of the C function description,
opens an external browser window displaying the FORTRAN90-specific 
information.  You will probably want to adjust the size and location of 
this external window so that both browser windows are visible and to 
facilitate moving easily between them.</i>
</font>

<table border=0 width=80%>
<tr><td valign=top width=40%>
<ul>
    <li><a href="#Reference-Create">h5rcreate_f</a>
    <li><a href="#Reference-Dereference">h5rdereference_f</a>
</ul>
</td><td valign=top width=40%>
<ul>
    <li><a href="#Reference-GetRegion">h5rget_region_f</a>
    <li><a href="#Reference-GetObjectType">h5rget_object_type_f</a>
</ul>
</td><td valign=top width=20%>
<ul>

</ul>
</td></tr>
</table>


<p>

<hr>
<dl>
<dt><strong>Name:</strong> <a name="Reference-Create">H5Rcreate</a>
<dt><strong>Signature:</strong>
    <dd><em>herr_t</em> <code>H5Rcreate</code>(<em>void *</em><code>ref</code>,
        <em>hid_t</em> <code>loc_id</code>,
        <em>const char *</em><code>name</code>,
        <em>H5R_type_t</em> <code>ref_type</code>,
        <em>hid_t</em> <code>space_id</code>
    )
<dt><strong>Purpose:</strong>
    <dd>Creates a reference.
<dt><strong>Description:</strong>
    <dd><code>H5Rcreate</code> creates the reference, <code>ref</code>,
        of the type specified in <code>ref_type</code>, pointing to 
        the object <code>name</code> located at <code>loc_id</code>.
        <p>
        The HDF5 library maps the <em>void</em> type specified above 
        for <code>ref</code> to the type specified in <code>ref_type</code>,
        which will be one of those appearing in the first column of
        the following table.  
        The second column of the table lists the HDF5 constant associated 
        with each reference type.
        <dir>
        <table border=0>
        <tr><td><em>hdset_reg_ref_t</em>&nbsp;&nbsp;</td>
            <td><code>H5R_DATASET_REGION</code>&nbsp;&nbsp;</td>
            <td>Dataset region reference</td></tr>
        <tr><td><em>hobj_ref_t</em></td>
            <td><code>H5R_OBJECT</code></td>
            <td>Object reference</td></tr>
        </table>
        </dir>
        <p>
        The parameters <code>loc_id</code> and <code>name</code> are 
        used to locate the object.
        <p>
        The parameter <code>space_id</code> identifies the region 
        to be pointed to for a dataset region reference.
        This parameter is unused with object references.  
<dt><strong>Parameters:</strong>
    <dl>
        <dt><em>void *</em><code>ref</code>
            <dd>OUT: Reference created by the function call.
        <dt><em>hid_t</em> <code>loc_id</code>
            <dd>IN: Location identifier used to locate the object being 
                    pointed to.
        <dt><em>const char *</em><code>name</code>
            <dd>IN: Name of object at location <code>loc_id</code>.
        <dt><em>H5R_type_t</em> <code>ref_type</code>
            <dd>IN: Type of reference.
        <dt><em>hid_t</em> <code>space_id</code>
            <dd>IN: Dataspace identifier with selection. 
                    Used for dataset region references. 
    </dl>
<dt><strong>Returns:</strong>
    <dd>Returns a non-negative value if successful;
        otherwise returns a negative value.
<dt><strong>Non-C API(s):</strong>
    <dd><a href="fortran/h5r_FORTRAN.html#h5rcreate_f" 
        target="FortranWin"><img src="Graphics/FORTRAN.gif" border=0></a>
        <!--
        <img src="Graphics/Java.gif"> 
        <img src="Graphics/C++.gif">
        -->
</dl>


<hr>
<dl>
<dt><strong>Name:</strong> <a name="Reference-Dereference">H5Rdereference</a>
<dt><strong>Signature:</strong>
    <dd><em>hid_t</em> <code>H5Rdereference</code>(<em>hid_t</em> <code>dataset</code>,
        <em>H5R_type_t</em> <code>ref_type</code>,
        <em>void *</em><code>ref</code>
    )
<dt><strong>Purpose:</strong>
    <dd>Opens the HDF5 object referenced.
<dt><strong>Description:</strong>
    <dd>Given a reference to some object, <code>H5Rdereference</code>
        opens that object and returns an identifier.
        <p>
        The parameter <code>ref_type</code> specifies the reference type
        of <code>ref</code>. 
        <code>ref_type</code> may contain either of the following values:
        <ul>
        <li><code>H5R_OBJECT</code>  (<code>0</code>)
        <li><code>H5R_DATASET_REGION</code>  (<code>1</code>)
        </ul>
<dt><strong>Parameters:</strong>
    <dl>
        <dt><em>hid_t</em> <code>dataset</code>
            <dd>IN: Dataset containing reference object.
        <dt><em>H5R_type_t</em> <code>ref_type</code>
            <dd>IN: The reference type of <code>ref</code>.
        <dt><em>void *</em><code>ref</code>
            <dd>IN: Reference to open.
    </dl>
<dt><strong>Returns:</strong>
    <dd>Returns valid identifier if successful;
        otherwise returns a negative value.
<dt><strong>Non-C API(s):</strong>
    <dd><a href="fortran/h5r_FORTRAN.html#h5rdereference_f" 
        target="FortranWin"><img src="Graphics/FORTRAN.gif" border=0></a>
        <!--
        <img src="Graphics/Java.gif"> 
        <img src="Graphics/C++.gif">
        -->
</dl>


<hr>
<dl>
<dt><strong>Name:</strong> <a name="Reference-GetRegion">H5Rget_region</a>
<dt><strong>Signature:</strong>
    <dd><em>hid_t</em> <code>H5Rget_region</code>(<em>hid_t</em> <code>dataset</code>,
    <em>H5R_type_t</em> <code>ref_type</code>,
    <em>void *</em><code>ref</code>
    )
<dt><strong>Purpose:</strong>
    <dd>Retrieves a dataspace with the specified region selected.
<dt><strong>Description:</strong>
    <dd>Given a reference to an object <code>ref</code>, 
        <code>H5Rget_region</code> creates a copy of the dataspace 
        of the dataset pointed to and defines a selection in the copy 
        which is the region pointed to.
        <p>
        The parameter <code>ref_type</code> specifies the reference type
        of <code>ref</code>. 
        <code>ref_type</code> may contain the following value:
        <ul>
        <li><code>H5R_DATASET_REGION</code>  (<code>1</code>)
        </ul>
<dt><strong>Parameters:</strong>
    <dl>
        <dt><em>hid_t</em> <code>dataset</code>,
            <dd>IN: Dataset containing reference object.
        <dt><em>H5R_type_t</em> <code>ref_type</code>,
            <dd>IN: The reference type of <code>ref</code>.
        <dt><em>void *</em><code>ref</code>
            <dd>IN: Reference to open.
    </dl>
<dt><strong>Returns:</strong>
    <dd>Returns a valid identifier if successful;
        otherwise returns a negative value.
<dt><strong>Non-C API(s):</strong>
    <dd><a href="fortran/h5r_FORTRAN.html#h5rget_region_f" 
        target="FortranWin"><img src="Graphics/FORTRAN.gif" border=0></a>
        <!--
        <img src="Graphics/Java.gif"> 
        <img src="Graphics/C++.gif">
        -->
</dl>


<hr>
<dl>
<dt><strong>Name:</strong> <a name="Reference-GetObjType">H5Rget_obj_type</a>
<dt><strong>Signature:</strong>
    <dd><em>H5G_obj_t</em> <code>H5Rget_obj_type</code>(<em>hid_t</em> <code>id</code>,
    <em>H5R_type_t</em> <code>ref_type</code>,
    <em>void *</em><code>ref</code>
    )
<dt><strong>Purpose:</strong>
    <dd>Retrieves the type of object that an object reference points to.
<dt><strong>Description:</strong>
    <dd>Given type of object reference, <code>ref_type</code>, 
        and a reference to an object, <code>ref</code>, 
        <code>H5Rget_obj_type</code> 
        returns the type of the referenced object.
	<p>
	Valid object reference types, to pass in as <code>ref_type</code>, 
	include the following:
	<table border="0">
	<tr align=left valign=top><td>&nbsp;&nbsp;&nbsp;&nbsp;</td><td>
	<code>H5R_OBJECT</code></td><td>
	Reference is an object reference.
	</td></tr>
	<tr align=left valign=top><td>&nbsp;</td><td>
	<code>H5R_DATASET_REGION&nbsp;&nbsp;</code></td><td>
	Reference is a dataset region reference.
	</td></tr>
	</table>
	<p>
	Valid object type return values include the following:
	<table border="0">
	<tr align=left valign=top><td>&nbsp;&nbsp;&nbsp;&nbsp;</td><td>
	<code>H5G_LINK</code></td><td>
	Object is a symbolic link.
	</td></tr>
	<tr align=left valign=top><td>&nbsp;</td><td>
	<code>H5G_GROUP</code></td><td>
	Object is a group.
	</td></tr>
	<tr align=left valign=top><td>&nbsp;</td><td>
	<code>H5G_DATASET&nbsp;&nbsp;</code></td><td>
	Object is a dataset.
	</td></tr>
	<tr align=left valign=top><td>&nbsp;</td><td>
	<code>H5G_TYPE</code></td><td>
	Object is a named datatype.
	</td></tr>
	</table>
<dt><strong>Parameters:</strong>
    <dl>
        <dt><em>hid_t</em> <code>id</code>,
            <dd>IN: The dataset containing the reference object or 
                the location identifier of the object that the 
                dataset is located within.
        <dt><em>H5R_type_t</em> <code>ref_type</code>
            <dd>IN: Type of reference to query.
        <dt><em>void *</em><code>ref</code>
            <dd>IN: Reference to query.
    </dl>
<dt><strong>Returns:</strong>
    <dd>Returns an object type as defined in <code>H5Gpublic.h</code> if successful;
        otherwise returns <code>H5G_UNKNOWN</code>.
<dt><strong>Non-C API(s):</strong>
    <dd><a href="fortran/h5r_FORTRAN.html#h5rget_object_type_f" 
        target="FortranWin"><img src="Graphics/FORTRAN.gif" border=0></a>
        <!--
        <img src="Graphics/Java.gif"> 
        <img src="Graphics/C++.gif">
        -->
</dl>


<hr>
<dl>
<dt><strong>Name:</strong> <a name="Reference-GetObjectType">H5Rget_object_type</a>
<dt><strong>Signature:</strong>
    <dd><em>int</em> <code>H5Rget_object_type</code>(<em>hid_t</em> <code>id</code>,
    <em>void *</em><code>ref</code>
    )
<dt><strong>Purpose:</strong>
    <dd>Retrieves the type of object that an object reference points to.
<dt><strong>Description:</strong>
    <dd>[<strong>NOTE:</strong>
        <span class="1_4_compat">
        This function is provided only to enable backward compatibility
        with HDF5 Releases 1.4.<i>x</i>. 
	This function is enabled only if the HDF5 library is configured 
	with the flag <code>H5_WANT_H5_V1_4_COMPAT</code> and is not
	enabled in the binaries distributed by NCSA.
	This function has been replaced in Release 1.6 by the function 
	<a href="#Reference-GetObjType"><code>H5Rget_obj_type</code></a>
	and will eventually be deleted from the HDF5 distribution.</span>]
        <p>
	</p>Given a reference to an object <code>ref</code>, 
        <code>H5Rget_object_type</code> returns the 
        type of the object pointed to.
<dt><strong>Parameters:</strong>
    <dl>
        <dt><em>hid_t</em> <code>id</code>,
            <dd>IN: The dataset containing the reference object or 
                the location identifier of the object that the dataset 
                is located within.
        <dt><em>void *</em><code>ref</code>
            <dd>IN: Reference to query.
    </dl>
<dt><strong>Returns:</strong>
    <dd>Returns an object type as defined in <code>H5Gpublic.h</code>;
        otherwise returns <code>H5G_UNKNOWN</code>.
<dt><strong>Non-C API(s):</strong>
    <dd><a href="fortran/h5r_FORTRAN.html#h5rget_object_type_f" 
        target="FortranWin"><img src="Graphics/FORTRAN.gif" border=0></a>
        <!--
        <img src="Graphics/Java.gif"> 
        <img src="Graphics/C++.gif">
        -->
</dl>


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<a href="mailto:hdfhelp@ncsa.uiuc.edu">HDF Help Desk</a> 
<br>
Describes HDF5 Release 1.6.0, July 2003
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Last modified: 25 June 2003 

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