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<html>
<head><title>
HDF5/H5A Draft API Specification
</title></head>
<body>
<center>
<h1>H5A: Attribute Interface</h1>
</center>
<h2>Attribute API Functions</h2>
These functions create and manipulate attributes
and information about attributes.
<table border=0>
<tr><td valign=top>
<ul>
<li><a href="#Annot-Create">H5Acreate</a>
<li><a href="#Annot-Write">H5Awrite</a>
<li><a href="#Annot-Read">H5Aread</a>
<li><a href="#Annot-Close">H5Aclose</a>
</ul>
</td><td> </td><td valign=top>
<ul>
<li><a href="#Annot-GetName">H5Aget_name</a>
<li><a href="#Annot-OpenName">H5Aopen_name</a>
<li><a href="#Annot-OpenIdx">H5Aopen_idx</a>
<li><a href="#Annot-GetSpace">H5Aget_space</a>
</ul>
</td><td> </td><td valign=top>
<ul>
<li><a href="#Annot-GetType">H5Aget_type</a>
<li><a href="#Annot-NumAttrs">H5Anum_attrs</a>
<li><a href="#Annot-Iterate">H5Aiterate</a>
<li><a href="#Annot-Delete">H5Adelete</a>
</ul>
</td></tr>
</table>
<hr>
<dl>
<dt><strong>Name:</strong> <a name="Annot-Create">H5Acreate</a>
<dt><strong>Signature:</strong>
<dd><em>hid_t</em> <code>H5Acreate</code>(<em>hid_t</em> <code>loc_id</code>,
<em>const char *</em><code>name</code>,
<em>hid_t</em> <code>datatype</code>,
<em>hid_t</em> <code>dataspace</code>,
<em>hid_t</em> <code>create_plist</code>
)
<dt><strong>Purpose:</strong>
<dd>Creates a dataset as an attribute of another dataset or group.
<dt><strong>Description:</strong>
<dd>SC: <code>H5Acreate</code> creates an attribute which is attached to the object
specified with 'location_id'. The name specified with 'name' for each
attribute for an object must be unique for that object. The 'type_id'
and 'space_id' are created with the H5T and H5S interfaces respectively.
Currently only simple dataspaces are allowed for attribute dataspaces.
The 'create_plist_id' property list is currently un-used, but will be
used int the future for optional properties of attributes. The attribute
identifier returned from this function must be released with H5Aclose or resource
leaks will develop.
<p>
The link created (see H5G API documentation for more information on
link types) is a hard link, so the attribute may be shared among datasets
and will not be removed from the file until the reference count for the
attribute is reduced to zero.
<p>
The location object may be either a group or a dataset, both of
which may have any sort of attribute.
<p>
UG: <code>H5Acreate</code> creates an attribute which is attached to the object
specified with <em>loc_id</em>. The name specified with <em>name</em>
for each attribute for an object must be unique for that object. The <em>type_id</em>
and <em>space_id</em> are created with the H5T and H5S interfaces
respectively. Currently only simple dataspaces are allowed for attribute
dataspaces. The <em>create_plist_id</em> property list is currently
unused, but will be used int the future for optional properties of
attributes. The attribute identifier returned from this function must be released
with H5Aclose or resource leaks will develop. Attempting to create an
attribute with the same name as an already existing attribute will fail,
leaving the pre-existing attribute in place.
<p>
<b>datatype, dataspace, create_plist in the UG are
type_id, space_id, and create_plist_id, respectively, in the SC</b>
<p>
<dt><strong>Parameters:</strong>
<dl>
<dt><em>hid_t</em> <code>loc_id</code>
<dd>IN: Object (dataset or group) to be attached to
<dt><em>const char *</em><code>name</code>
<dd>IN: Name of attribute to create
<dt><em>hid_t</em> <code>datatype</code>
<dd>IN: Identifier of datatype for attribute
<dt><em>hid_t</em> <code>dataspace</code>
<dd>IN: Identifier of dataspace for attribute
<dt><em>hid_t</em> <code>create_plist</code>
<dd>IN: Identifier of creation property list (currently not used)
</dl>
<dt><strong>Returns:</strong>
<dd>Returns an attribute identifier if successful;
otherwise FAIL (-1).
</dl>
<hr>
<dl>
<dt><strong>Name:</strong> <a name="Annot-OpenName">H5Aopen_name</a>
<dt><strong>Signature:</strong>
<dd><em>hid_t</em> <code>H5Aopen_name</code>(<em>hid_t</em> <code>loc_id</code>,
<em>const char *</em><code>name</code>
)
<dt><strong>Purpose:</strong>
<dd> Opens an attribute for an object by looking up the attribute name.
<dt><strong>Description:</strong>
<dd> SC: <code>H5Aopen_name</code> opens an existing attribute for access. The attribute
name specified is used to look up the corresponding attribute for the
object. The attribute identifier returned from this function must be released with
H5Aclose or resource leaks will develop.
<p>
The location object may be either a group or a dataset, both of
which may have any sort of attribute.
<p>
UG: <code>H5Aopen_name</code> opens an attribute which is attached to the object
specified with loc_id. The name specified with name indicates the
attribute to access. The attribute identifier returned from this function must
be released with H5Aclose or resource leaks will develop.
<dt><strong>Parameters:</strong>
<dl>
<dt><em>hid_t</em> <code>loc_id</code>
<dd>IN: Object (dataset or group) to be attached to
<dt><em>const char *</em><code>name</code>
<dd>IN: Name of attribute to locate and open
</dl>
<dt><strong>Returns:</strong>
<dd>Returns attribute identifier if successful;
otherwise FAIL (-1).
</dl>
<hr>
<dl>
<dt><strong>Name:</strong> <a name="Annot-OpenIdx">H5Aopen_idx</a>
<dt><strong>Signature:</strong>
<dd><em>hid_t</em> <code>H5Aopen_idx</code>(<em>hid_t</em> <code>loc_id</code>,
<em>unsigned int</em> <code>idx</code>
)
<dt><strong>Purpose:</strong>
<dd>Opens the <i>n</i>th attribute for an object.
<dt><strong>Description:</strong>
<dd>SC: <code>H5Aopen_idx</code> opens an existing attribute for access. The attribute
index specified is used to look up the corresponding attribute for the
object. The attribute identifier returned from this function must be released with
H5Aclose or resource leaks will develop.
<p>
The location object may be either a group or a dataset, both of
which may have any sort of attribute.
<p>
UG: <code>H5Aopen_idx</code> opens an attribute which is attached to the object
specified with loc_id. The attribute specified with idx indicates the
<i>idx</i>th attribute to access, starting with '0'.
The attribute identifier returned from this function must be released with
H5Aclose or resource leaks will develop.
<dt><strong>Parameters:</strong>
<dl>
<dt><em>hid_t</em> <code>loc_id</code>
<dd>IN: Object (dataset or group) to be attached to
<dt><em>unsigned int</em> <code>idx</code>
<dd>IN: Index (0-based) attribute to open
</dl>
<dt><strong>Returns:</strong>
<dd>Returns attribute identifier if successful;
otherwise FAIL (-1).
</dl>
<hr>
<dl>
<dt><strong>Name:</strong> <a name="Annot-Write">H5Awrite</a>
<dt><strong>Signature:</strong>
<dd><em>herr_t</em> <code>H5Awrite</code>(<em>hid_t</em> <code>attr_id</code>,
<em>hid_t</em> <code>mem_dt</code>,
<em>void *</em><code>buf</code>
)
<dt><strong>Purpose:</strong>
<dd>Write out data to an attribute.
<dt><strong>Description:</strong>
<dd>SC: <code>H5Awrite</code> writes a complete attribute to disk.
<p>
UG: <code>H5Awrite</code> writes an attribute, specified with attr_id,
with mem_type_id specifying the datatype in memory.
The entire attribute is written from buf to the file.
This function returns non-negative on success, negative on failure.
<p>
<b>mem_dt in SC is mem_type_id in UG.</b>
<p>
<dt><strong>Parameters:</strong>
<dl>
<dt><em>hid_t</em> <code>attr_id</code>
<dd>IN: Attribute to write
<dt><em>hid_t</em> <code>mem_dt</code>
<dd>IN: Memory datatype of buffer
<dt><em>void *</em><code>buf</code>
<dd>IN: Buffer of data to write
</dl>
<dt><strong>Returns:</strong>
<dd>Returns SUCCEED (0) if successful;
otherwise FAIL (-1).
</dl>
<hr>
<dl>
<dt><strong>Name:</strong> <a name="Annot-Read">H5Aread</a>
<dt><strong>Signature:</strong>
<dd><em>herr_t</em> <code>H5Aread</code>(<em>hid_t</em> <code>attr_id</code>,
<em>hid_t</em> <code>mem_dt</code>,
<em>void *</em><code>buf</code>
)
<dt><strong>Purpose:</strong>
<dd>Read in data from an attribute.
<dt><strong>Description:</strong>
<dd>SC: <code>H5Aread</code> reads a complete attribute from disk.
<p>
UG: <code>H5Aread</code> reads an attribute, specified with attr_id,
with mem_type_id specifying the datatype in memory.
The entire attribute is read into buf from the file.
This function returns non-negative on success, negative on failure.
<p>
<b>mem_dt in SC is mem_type_id in UG.</b>
<p>
<dt><strong>Parameters:</strong>
<dl>
<dt><em>hid_t</em> <code>attr_id</code>
<dd>IN: Attribute to read
<dt><em>hid_t</em> <code>mem_dt</code>
<dd>IN: Memory datatype of buffer
<dt><em>void *</em><code>buf</code>
<dd>IN: Buffer for data to read
</dl>
<dt><strong>Returns:</strong>
<dd>Returns SUCCEED (0) if successful;
otherwise FAIL (-1).
</dl>
<hr>
<dl>
<dt><strong>Name:</strong> <a name="Annot-GetSpace">H5Aget_space</a>
<dt><strong>Signature:</strong>
<dd><em>hid_t</em> <code>H5Aget_space</code>(<em>hid_t</em> <code>attr_id</code>)
<dt><strong>Purpose:</strong>
<dd>Gets a copy of the dataspace for an attribute.
<dt><strong>Description:</strong>
<dd><code>H5Aget_space</code> retrieves a copy of the dataspace for an attribute.
The dataspace identifier returned from this function must be released with H5Sclose
or resource leaks will develop.
<p>
<i>(Identical desc in UG and SC.)</i>
<p>
<dt><strong>Parameters:</strong>
<dl>
<dt><em>hid_t</em> <code>attr_id</code>
<dd>IN: Attribute to get dataspace of
</dl>
<dt><strong>Returns:</strong>
<dd>Returns dataspace identifier if successful;
otherwise FAIL (-1).
</dl>
<hr>
<dl>
<dt><strong>Name:</strong> <a name="Annot-GetType">H5Aget_type</a>
<dt><strong>Signature:</strong>
<dd><em>hid_t</em> <code>H5Aget_type</code>(<em>hid_t</em> <code>attr_id</code>)
<dt><strong>Purpose:</strong>
<dd>Gets a copy of the datatype for an attribute.
<dt><strong>Description:</strong>
<dd><code>H5Aget_type</code> retrieves a copy of the datatype for an attribute.
The datatype identifier returned from this function must be released with
H5Tclose or resource leaks will develop.
<p>
<i>(Identical desc in UG and SC.)</i>
<p>
<dt><strong>Parameters:</strong>
<dl>
<dt><em>hid_t</em> <code>attr_id</code>
<dd>IN: Attribute to get datatype of
</dl>
<dt><strong>Returns:</strong>
<dd>Returns a datatype identifier if successful;
otherwise FAIL (-1).
</dl>
<hr>
<dl>
<dt><strong>Name:</strong> <a name="Annot-GetName">H5Aget_name</a>
<dt><strong>Signature:</strong>
<dd><em>size_t</em> <code>H5Aget_name</code>(<em>hid_t</em> <code>attr_id</code>,
<em>char *</em><code>buf</code>,
<em>size_t</em> <code>buf_size</code>
)
<dt><strong>Purpose:</strong>
<dd>Gets a copy of the name for an attribute.
<dt><strong>Description:</strong>
<dd><code>H5Aget_name</code> retrieves the name of an attribute for an attribute identifier.
Up to 'buf_size' characters are stored in 'buf' followed by a '\0' string
terminator. If the name of the attribute is longer than 'buf_size'-1,
the string terminator is stored in the last position of the buffer to
properly terminate the string.
<p>
<i>(Identical desc in UG and SC.)</i>
<p>
<dt><strong>Parameters:</strong>
<dl>
<dt><em>hid_t</em> <code>attr_id</code>
<dd>IN: Attribute to get name of
<dt><em>char *</em><code>buf</code>
<dd>IN: Buffer to store name in
<dt><em>size_t</em> <code>buf_size</code>
<dd>IN: The size of the buffer to store the string in
</dl>
<dt><strong>Returns:</strong>
<dd>Returns the length of the attribute's name, which may be
longer than <code>buf_size</code>, if successful.
Otherwise returns FAIL (-1).
</dl>
<hr>
<dl>
<dt><strong>Name:</strong> <a name="Annot-NumAttrs">H5Anum_attrs</a>
<dt><strong>Signature:</strong>
<dd><em>int</em> <code>H5Anum_attrs</code>(<em>hid_t</em> <code>loc_id</code>)
<dt><strong>Purpose:</strong>
<dd>Determines the number of attributes attached to an object.
<dt><strong>Description:</strong>
<dd><code>H5Anum_attrs</code> returns the number of attributes attached to the dataset or
group, <code>loc_id</code>.
<p>
<i>(Identical desc in UG and SC.)</i>
<p>
<dt><strong>Parameters:</strong>
<dl>
<dt><em>hid_t</em> <code>loc_id</code>
<dd>IN: The object, a dataset or group, to be queried
</dl>
<dt><strong>Returns:</strong>
<dd>Returns the number of attributes if successful;
otherwise FAIL (-1).
</dl>
<hr>
<dl>
<dt><strong>Name:</strong> <a name="Annot-Iterate">H5Aiterate</a>
<dt><strong>Signature:</strong>
<dd><em>int</em> <code>H5Aiterate</code>(<em>hid_t</em> <code>loc_id</code>,
<em>unsigned *</em> <code>attr_num</code>,
<em>H5A_operator_t</em> <code>op</code>,
<em>void *</em><code>op_data</code>
)
<dt><strong>Purpose:</strong>
<dd>Calls a user's function for each attribute on an object.
<dt><strong>Description:</strong>
<dd>SC: H5Aiterate interates over the attributes of dataset or group
specified with 'loc_id'. For each attribute of the object, the
'op_data' and some additional information (specified below) are passed
to the 'op' function. The iteration begins with the '*attr_number'
object in the group and the next attribute to be processed by the operator
is returned in '*attr_number'.
<p>
The operation receives the identifier for the group or dataset being iterated
over ('loc_id'), the name of the current attribute about the object
('attr_name') and the pointer to the operator data passed in to H5Aiterate
('op_data'). The return values from an operator are:
<ul>
<li>Zero causes the iterator to continue, returning zero when all
attributes have been processed.
<li>Positive causes the iterator to immediately return that positive
value, indicating short-circuit success. The iterator can be
restarted at the next attribute.
<li>Negative causes the iterator to immediately return that value,
indicating failure. The iterator can be restarted at the next
attribute.
</ul>
<dd>UG: <code>H5Aiterate</code> interates over the attributes of dataset or group
specified with loc_id. For each attribute of the object,
the operator_data and some additional information (specified below)
are passed to the operator function. The iteration begins with
the *attr_number object in the group and the next attribute to be
processed by the operator is returned in *attr_number.
<p>
The prototype for H5A_operator_t is: <br>
<code>typedef herr_t (*H5A_operator_t)(hid_t <em>loc_id</em>,
const char *<em>attr_name</em>, void *<em>operator_data</em>);</code>
<p>
The operation receives the identifier for the group or dataset being iterated over
(<em>loc_id</em>), the name of the current attribute about the object (<em>attr_name</em>)
and the pointer to the operator data passed in to H5Aiterate
(<em>operator_data</em>). The return values from an operator are:
<ul>
<li>Zero causes the iterator to continue, returning zero when all
attributes have been processed.
<li>Positive causes the iterator to immediately return that positive
value, indicating short-circuit success. The iterator can be
restarted at the next attribute.
<li>Negative causes the iterator to immediately return that value,
indicating failure. The iterator can be restarted at the next
attribute.
</ul>
<dd><b>attr_num, op, and op_data in SC are
attr_number, operator, and operator_data, respectively, in UG.</b>
<p>
<dt><strong>Parameters:</strong>
<dl>
<dt><em>hid_t</em> <code>loc_id</code>
<dd>IN: Object (dataset or group) to be iterated over
<dt><em>unsigned *</em> <code>attr_num</code>
<dd>IN/OUT: Starting (IN) & Ending (OUT) attribute number
<dt><em>H5A_operator_t</em> <code>op</code>
<dd>IN: User's function to pass each attribute to
<dt><em>void *</em><code>op_data</code>
<dd>IN/OUT: User's data to pass through to iterator operator function
</dl>
<dt><strong>Returns:</strong>
<dd>If successful, returns the return value of the last operator
if it was non-zero, or zero if all attributes were processed.
Otherwise returns FAIL (-1).
</dl>
<hr>
<dl>
<dt><strong>Name:</strong> <a name="Annot-Delete">H5Adelete</a>
<dt><strong>Signature:</strong>
<dd><em>herr_t</em> <code>H5Adelete</code>(<em>hid_t</em> <code>loc_id</code>,
<em>const char *</em><code>name</code>
)
<dt><strong>Purpose:</strong>
<dd>Deletes an attribute from a location.
<dt><strong>Description:</strong>
<dd>SC: <code>H5Adelete</code> removes the named attribute from a dataset or group.
This function should not be used when attribute identifiers are open on 'loc_id'
as it may cause the internal indexes of the attributes to change and future
writes to the open attributes to produce incorrect results.
<p>
UG: <code>H5Adelete</code> removes the named attribute from a dataset or group.
This function should not be used when attribute identifiers are open on loc_id as
it may cause the internal indexes of the attributes to change and future
writes to the open attributes to produce incorrect results.
Returns non-negative on success, negative on failure.
<dt><strong>Parameters:</strong>
<dl>
<dt><em>hid_t</em> <code>loc_id</code>
<dd>IN: Object (dataset or group) to have attribute deleted from
<dt><em>const char *</em><code>name</code>
<dd>IN: Name of attribute to delete
</dl>
<dt><strong>Returns:</strong>
<dd>Returns SUCCEED (0) if successful;
otherwise FAIL (-1).
</dl>
<hr>
<dl>
<dt><strong>Name:</strong> <a name="Annot-Close">H5Aclose</a>
<dt><strong>Signature:</strong>
<dd><em>herr_t</em> <code>H5Aclose</code>(<em>hid_t</em> <code>attr_id</code>)
<dt><strong>Purpose:</strong>
<dd>Close an attribute identifier.
<dt><strong>Description:</strong>
<dd>SC: <code>H5Aclose</code> releases an attribute from use. Further use of the
attribute identifier will result in undefined behavior.
<p>
UG: <code>H5Aclose</code> releases an attribute from use.
Further use of the attribute identifier will result in undefined behavior.
This function returns non-negative on success, negative on failure.
<dt><strong>Parameters:</strong>
<dl>
<dt><em>hid_t</em> <code>attr_id</code>
<dd>IN: Attribute to release access to
</dl>
<dt><strong>Returns:</strong>
<dd>Returns SUCCEED (0) if successful;
otherwise FAIL (-1).
</dl>
<hr>
<address>
<a href="mailto:fbaker@ncsa.uiuc.edu">Frank Baker</a>
<br>
<a href="mailto:h5docs@ncsa.uiuc.edu">HDF5 Documentation</a>
<br>
Last modified: 6 July 1998
</body>
</html>
|
