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

<body bgcolor="#FFFFFF">


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<center>
<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>


<table border=0 width=98%>
<tr><td valign=top width=33%>
<ul>
    <li><a href="#Reference-Create">H5Rcreate</a>
    <li><a href="#Reference-Dereference">H5Rdereference</a>
</ul>
</td><td valign=top width=33%>
<ul>
    <li><a href="#Reference-GetRegion">H5Rget_region</a>
    <li><a href="#Reference-GetObjectType">H5Rget_object_type</a>
</ul>
</td><td valign=top width=34%>
<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 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 dataset region 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.
</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.
</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.
</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>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>.
</dl>


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

<br>
Last modified:  30 October 1998

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