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<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<title>GNOME Data Access 5 manual: Blobs</title>
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<table class="navigation" id="top" width="100%" summary="Navigation header" cellpadding="2" cellspacing="10"><tr valign="middle">
<td width="100%" align="left" class="shortcuts">
<a href="#" class="shortcut">Top</a><span id="nav_description"> <span class="dim">|</span> 
                  <a href="#GdaBlobOp.description" class="shortcut">Description</a></span><span id="nav_hierarchy"> <span class="dim">|</span> 
                  <a href="#GdaBlobOp.object-hierarchy" class="shortcut">Object Hierarchy</a></span>
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<td><a accesskey="u" href="data_models.html"><img src="up.png" width="16" height="16" border="0" alt="Up"></a></td>
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</tr></table>
<div class="refentry">
<a name="GdaBlobOp"></a><div class="titlepage"></div>
<div class="refnamediv"><table width="100%"><tr>
<td valign="top">
<h2><span class="refentrytitle"><a name="GdaBlobOp.top_of_page"></a>Blobs</span></h2>
<p>Blobs — Binary data and BLOBs handling</p>
</td>
<td class="gallery_image" valign="top" align="right"></td>
</tr></table></div>
<div class="refsect1">
<a name="GdaBlobOp.stability-level"></a><h2>Stability Level</h2>
Stable, unless otherwise indicated
</div>
<div class="refsect1">
<a name="GdaBlobOp.functions"></a><h2>Functions</h2>
<div class="informaltable"><table width="100%" border="0">
<colgroup>
<col width="150px" class="functions_return">
<col class="functions_name">
</colgroup>
<tbody>
<tr>
<td class="function_type">
<a href="/usr/share/gtk-doc/html/glib/glib-Basic-Types.html#glong"><span class="returnvalue">glong</span></a>
</td>
<td class="function_name">
<a class="link" href="GdaBlobOp.html#gda-blob-op-get-length" title="gda_blob_op_get_length ()">gda_blob_op_get_length</a> <span class="c_punctuation">()</span>
</td>
</tr>
<tr>
<td class="function_type">
<a href="/usr/share/gtk-doc/html/glib/glib-Basic-Types.html#glong"><span class="returnvalue">glong</span></a>
</td>
<td class="function_name">
<a class="link" href="GdaBlobOp.html#gda-blob-op-read" title="gda_blob_op_read ()">gda_blob_op_read</a> <span class="c_punctuation">()</span>
</td>
</tr>
<tr>
<td class="function_type">
<a href="/usr/share/gtk-doc/html/glib/glib-Basic-Types.html#gboolean"><span class="returnvalue">gboolean</span></a>
</td>
<td class="function_name">
<a class="link" href="GdaBlobOp.html#gda-blob-op-read-all" title="gda_blob_op_read_all ()">gda_blob_op_read_all</a> <span class="c_punctuation">()</span>
</td>
</tr>
<tr>
<td class="function_type">
<a href="/usr/share/gtk-doc/html/glib/glib-Basic-Types.html#glong"><span class="returnvalue">glong</span></a>
</td>
<td class="function_name">
<a class="link" href="GdaBlobOp.html#gda-blob-op-write" title="gda_blob_op_write ()">gda_blob_op_write</a> <span class="c_punctuation">()</span>
</td>
</tr>
<tr>
<td class="function_type">
<a href="/usr/share/gtk-doc/html/glib/glib-Basic-Types.html#gboolean"><span class="returnvalue">gboolean</span></a>
</td>
<td class="function_name">
<a class="link" href="GdaBlobOp.html#gda-blob-op-write-all" title="gda_blob_op_write_all ()">gda_blob_op_write_all</a> <span class="c_punctuation">()</span>
</td>
</tr>
</tbody>
</table></div>
</div>
<div class="refsect1">
<a name="GdaBlobOp.other"></a><h2>Types and Values</h2>
<div class="informaltable"><table width="100%" border="0">
<colgroup>
<col width="150px" class="name">
<col class="description">
</colgroup>
<tbody><tr>
<td class="datatype_keyword"> </td>
<td class="function_name"><a class="link" href="GdaBlobOp.html#GdaBlobOp-struct" title="GdaBlobOp">GdaBlobOp</a></td>
</tr></tbody>
</table></div>
</div>
<div class="refsect1">
<a name="GdaBlobOp.object-hierarchy"></a><h2>Object Hierarchy</h2>
<pre class="screen">    <a href="/usr/share/gtk-doc/html/gobject/gobject-The-Base-Object-Type.html#GObject">GObject</a>
    <span class="lineart">╰──</span> GdaBlobOp
</pre>
</div>
<div class="refsect1">
<a name="GdaBlobOp.includes"></a><h2>Includes</h2>
<pre class="synopsis">#include &lt;libgda/gda-blob-op.h&gt;
</pre>
</div>
<div class="refsect1">
<a name="GdaBlobOp.description"></a><h2>Description</h2>
<p>This object is a base class for individual database providers which support BLOB types. It supports
operations to read and write data in a BLOB value (of type GDA_BLOB_TYPE).</p>
<p>Libgda offers two methods to manipulate binary values as two containers: <a class="link" href="libgda-5.0-Gda-Value.html#GdaBinary">GdaBinary</a>
and <a class="link" href="libgda-5.0-Gda-Value.html#GdaBlob" title="GdaBlob">GdaBlob</a>:</p>
<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem"><p>When reading from a data model returned by <span class="application">Libgda</span> binary data will often be in a GdaBlob
  object, and the associated <a class="link" href="GdaBlobOp.html" title="Blobs">GdaBlobOp</a> object can be used to manipulate the
  binary object (in a database for example)</p></li>
<li class="listitem"><p>When the binary value is created by the user, then there is no point in using a GdaBlob as
  there can not be any <a class="link" href="GdaBlobOp.html" title="Blobs">GdaBlobOp</a> object, so the GdaBinary container is
  enough.</p></li>
</ul></div>
<p>Note that a <a class="link" href="libgda-5.0-Gda-Value.html#GdaBlob" title="GdaBlob">GdaBlob</a> value (the "data" attribute) will often not contain any data
(or only some part of the actual BLOB)
and that it's up to the user to use the associated <a class="link" href="GdaBlobOp.html" title="Blobs">GdaBlobOp</a> object to
"load" the data into the container (into the actual process heap).</p>
<p>For example to load the 1st 40 bytes of a blob:</p>
<pre class="programlisting">
GValue *blob_value = ...
GdaBlob *blob;

blob = (GdaBlob*) gda_value_get_blob (blob_value);
gda_blob_op_read (blob-&gt;op, blob, 0, 40);
 </pre>
<p>Another example is to write the contents of a blob to a file on disk, using a special</p>
<a class="link" href="GdaBlobOp.html" title="Blobs">GdaBlobOp</a> object (internal to <span class="application">Libgda</span> which interfaces
<p> with a file in a filesystem):</p>
<pre class="programlisting">
GValue *blob_value; // value to copy from
GValue *tmp_value;
GdaBlob *file_blob;

GValue *blob_value = ...
tmp_value = gda_value_new_blob_from_file ("MyFile.bin");
file_blob = (GdaBlob*) gda_value_get_blob (tmp_value);

if (! gda_blob_op_write_all (file_blob-&gt;op, gda_value_get_blob (blob_value))) {
      // error
}
else {
      gsize size;
      size = gda_blob_op_get_length (file_blob-&gt;op);
      g_print ("Wrote %s, size = %d\n", filename, size);
}
gda_value_free (tmp_value);
 </pre>
<p>For further information, see:</p>
<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem"><p>the section about <a class="link" href="gen_blobs.html" title="Binary large objects (BLOBs)">Binary large objects (BLOBs)</a>'s
       abstraction</p></li>
<li class="listitem"><p><a class="link" href="libgda-provider-blobop.html" title="Virtual methods for Blob operations">Virtual methods for Blob operations</a>
       section for more information
       about how to implement the virtual methods when creating a database provider</p></li>
</ul></div>
</div>
<div class="refsect1">
<a name="GdaBlobOp.functions_details"></a><h2>Functions</h2>
<div class="refsect2">
<a name="gda-blob-op-get-length"></a><h3>gda_blob_op_get_length ()</h3>
<pre class="programlisting"><a href="/usr/share/gtk-doc/html/glib/glib-Basic-Types.html#glong"><span class="returnvalue">glong</span></a>
gda_blob_op_get_length (<em class="parameter"><code><a class="link" href="GdaBlobOp.html" title="Blobs"><span class="type">GdaBlobOp</span></a> *op</code></em>);</pre>
<div class="refsect3">
<a name="id-1.3.8.6.9.2.4"></a><h4>Parameters</h4>
<div class="informaltable"><table width="100%" border="0">
<colgroup>
<col width="150px" class="parameters_name">
<col class="parameters_description">
<col width="200px" class="parameters_annotations">
</colgroup>
<tbody><tr>
<td class="parameter_name"><p>op</p></td>
<td class="parameter_description"><p>an existing <a class="link" href="GdaBlobOp.html" title="Blobs"><span class="type">GdaBlobOp</span></a></p></td>
<td class="parameter_annotations"> </td>
</tr></tbody>
</table></div>
</div>
<div class="refsect3">
<a name="id-1.3.8.6.9.2.5"></a><h4>Returns</h4>
<p> the length of the blob in bytes. In case of error, -1 is returned and the
provider should have added an error (a <a class="link" href="GdaConnectionEvent.html" title="GdaConnectionEvent"><span class="type">GdaConnectionEvent</span></a>) to the connection.</p>
<p></p>
</div>
</div>
<hr>
<div class="refsect2">
<a name="gda-blob-op-read"></a><h3>gda_blob_op_read ()</h3>
<pre class="programlisting"><a href="/usr/share/gtk-doc/html/glib/glib-Basic-Types.html#glong"><span class="returnvalue">glong</span></a>
gda_blob_op_read (<em class="parameter"><code><a class="link" href="GdaBlobOp.html" title="Blobs"><span class="type">GdaBlobOp</span></a> *op</code></em>,
                  <em class="parameter"><code><a class="link" href="libgda-5.0-Gda-Value.html#GdaBlob" title="GdaBlob"><span class="type">GdaBlob</span></a> *blob</code></em>,
                  <em class="parameter"><code><a href="/usr/share/gtk-doc/html/glib/glib-Basic-Types.html#glong"><span class="type">glong</span></a> offset</code></em>,
                  <em class="parameter"><code><a href="/usr/share/gtk-doc/html/glib/glib-Basic-Types.html#glong"><span class="type">glong</span></a> size</code></em>);</pre>
<p>Reads a chunk of bytes from the BLOB accessible through <em class="parameter"><code>op</code></em>
 into <em class="parameter"><code>blob</code></em>
.</p>
<div class="refsect3">
<a name="id-1.3.8.6.9.3.5"></a><h4>Parameters</h4>
<div class="informaltable"><table width="100%" border="0">
<colgroup>
<col width="150px" class="parameters_name">
<col class="parameters_description">
<col width="200px" class="parameters_annotations">
</colgroup>
<tbody>
<tr>
<td class="parameter_name"><p>op</p></td>
<td class="parameter_description"><p>a <a class="link" href="GdaBlobOp.html" title="Blobs"><span class="type">GdaBlobOp</span></a></p></td>
<td class="parameter_annotations"> </td>
</tr>
<tr>
<td class="parameter_name"><p>blob</p></td>
<td class="parameter_description"><p>a <a class="link" href="libgda-5.0-Gda-Value.html#GdaBlob" title="GdaBlob"><span class="type">GdaBlob</span></a> to read data to</p></td>
<td class="parameter_annotations"> </td>
</tr>
<tr>
<td class="parameter_name"><p>offset</p></td>
<td class="parameter_description"><p>offset to read from the start of the blob (starts at 0)</p></td>
<td class="parameter_annotations"> </td>
</tr>
<tr>
<td class="parameter_name"><p>size</p></td>
<td class="parameter_description"><p>maximum number of bytes to read.</p></td>
<td class="parameter_annotations"> </td>
</tr>
</tbody>
</table></div>
</div>
<div class="refsect3">
<a name="id-1.3.8.6.9.3.6"></a><h4>Returns</h4>
<p> the number of bytes actually read. In case of error, -1 is returned and the
provider should have added an error to the connection.</p>
<p></p>
</div>
</div>
<hr>
<div class="refsect2">
<a name="gda-blob-op-read-all"></a><h3>gda_blob_op_read_all ()</h3>
<pre class="programlisting"><a href="/usr/share/gtk-doc/html/glib/glib-Basic-Types.html#gboolean"><span class="returnvalue">gboolean</span></a>
gda_blob_op_read_all (<em class="parameter"><code><a class="link" href="GdaBlobOp.html" title="Blobs"><span class="type">GdaBlobOp</span></a> *op</code></em>,
                      <em class="parameter"><code><a class="link" href="libgda-5.0-Gda-Value.html#GdaBlob" title="GdaBlob"><span class="type">GdaBlob</span></a> *blob</code></em>);</pre>
<p>Reads the whole contents of the blob manipulated by <em class="parameter"><code>op</code></em>
 into <em class="parameter"><code>blob</code></em>
</p>
<div class="refsect3">
<a name="id-1.3.8.6.9.4.5"></a><h4>Parameters</h4>
<div class="informaltable"><table width="100%" border="0">
<colgroup>
<col width="150px" class="parameters_name">
<col class="parameters_description">
<col width="200px" class="parameters_annotations">
</colgroup>
<tbody>
<tr>
<td class="parameter_name"><p>op</p></td>
<td class="parameter_description"><p>a <a class="link" href="GdaBlobOp.html" title="Blobs"><span class="type">GdaBlobOp</span></a></p></td>
<td class="parameter_annotations"> </td>
</tr>
<tr>
<td class="parameter_name"><p>blob</p></td>
<td class="parameter_description"><p>a <a class="link" href="libgda-5.0-Gda-Value.html#GdaBlob" title="GdaBlob"><span class="type">GdaBlob</span></a> to read data to</p></td>
<td class="parameter_annotations"> </td>
</tr>
</tbody>
</table></div>
</div>
<div class="refsect3">
<a name="id-1.3.8.6.9.4.6"></a><h4>Returns</h4>
<p> TRUE if <em class="parameter"><code>blob-&gt;data</code></em>
contains the whole BLOB manipulated by <em class="parameter"><code>op</code></em>
</p>
<p></p>
</div>
</div>
<hr>
<div class="refsect2">
<a name="gda-blob-op-write"></a><h3>gda_blob_op_write ()</h3>
<pre class="programlisting"><a href="/usr/share/gtk-doc/html/glib/glib-Basic-Types.html#glong"><span class="returnvalue">glong</span></a>
gda_blob_op_write (<em class="parameter"><code><a class="link" href="GdaBlobOp.html" title="Blobs"><span class="type">GdaBlobOp</span></a> *op</code></em>,
                   <em class="parameter"><code><a class="link" href="libgda-5.0-Gda-Value.html#GdaBlob" title="GdaBlob"><span class="type">GdaBlob</span></a> *blob</code></em>,
                   <em class="parameter"><code><a href="/usr/share/gtk-doc/html/glib/glib-Basic-Types.html#glong"><span class="type">glong</span></a> offset</code></em>);</pre>
<p>Writes a chunk of bytes from a <em class="parameter"><code>blob</code></em>
 to the BLOB accessible through <em class="parameter"><code>op</code></em>
, <em class="parameter"><code>blob</code></em>
 is unchanged after
this call.</p>
<p>If <em class="parameter"><code>blob</code></em>
 has an associated <a class="link" href="GdaBlobOp.html" title="Blobs"><span class="type">GdaBlobOp</span></a> (ie. if <em class="parameter"><code>blob-&gt;op</code></em>
 is not <a href="/usr/share/gtk-doc/html/glib/glib-Standard-Macros.html#NULL:CAPS"><code class="literal">NULL</code></a>) then the data to be written
using <em class="parameter"><code>op</code></em>
 is the data fetched using <em class="parameter"><code>blob-&gt;op</code></em>
.</p>
<div class="refsect3">
<a name="id-1.3.8.6.9.5.6"></a><h4>Parameters</h4>
<div class="informaltable"><table width="100%" border="0">
<colgroup>
<col width="150px" class="parameters_name">
<col class="parameters_description">
<col width="200px" class="parameters_annotations">
</colgroup>
<tbody>
<tr>
<td class="parameter_name"><p>op</p></td>
<td class="parameter_description"><p>a <a class="link" href="GdaBlobOp.html" title="Blobs"><span class="type">GdaBlobOp</span></a></p></td>
<td class="parameter_annotations"> </td>
</tr>
<tr>
<td class="parameter_name"><p>blob</p></td>
<td class="parameter_description"><p>a <a class="link" href="libgda-5.0-Gda-Value.html#GdaBlob" title="GdaBlob"><span class="type">GdaBlob</span></a> which contains the data to write</p></td>
<td class="parameter_annotations"> </td>
</tr>
<tr>
<td class="parameter_name"><p>offset</p></td>
<td class="parameter_description"><p>offset to write from the start of the blob (starts at 0)</p></td>
<td class="parameter_annotations"> </td>
</tr>
</tbody>
</table></div>
</div>
<div class="refsect3">
<a name="id-1.3.8.6.9.5.7"></a><h4>Returns</h4>
<p> the number of bytes written. In case of error, -1 is returned and the
provider should have added an error to the connection.</p>
<p></p>
</div>
</div>
<hr>
<div class="refsect2">
<a name="gda-blob-op-write-all"></a><h3>gda_blob_op_write_all ()</h3>
<pre class="programlisting"><a href="/usr/share/gtk-doc/html/glib/glib-Basic-Types.html#gboolean"><span class="returnvalue">gboolean</span></a>
gda_blob_op_write_all (<em class="parameter"><code><a class="link" href="GdaBlobOp.html" title="Blobs"><span class="type">GdaBlobOp</span></a> *op</code></em>,
                       <em class="parameter"><code><a class="link" href="libgda-5.0-Gda-Value.html#GdaBlob" title="GdaBlob"><span class="type">GdaBlob</span></a> *blob</code></em>);</pre>
<p>Writes the whole contents of <em class="parameter"><code>blob</code></em>
 into the blob manipulated by <em class="parameter"><code>op</code></em>
. If necessary the resulting
blob is truncated from its previous length.</p>
<div class="refsect3">
<a name="id-1.3.8.6.9.6.5"></a><h4>Parameters</h4>
<div class="informaltable"><table width="100%" border="0">
<colgroup>
<col width="150px" class="parameters_name">
<col class="parameters_description">
<col width="200px" class="parameters_annotations">
</colgroup>
<tbody>
<tr>
<td class="parameter_name"><p>op</p></td>
<td class="parameter_description"><p>a <a class="link" href="GdaBlobOp.html" title="Blobs"><span class="type">GdaBlobOp</span></a></p></td>
<td class="parameter_annotations"> </td>
</tr>
<tr>
<td class="parameter_name"><p>blob</p></td>
<td class="parameter_description"><p>a <a class="link" href="libgda-5.0-Gda-Value.html#GdaBlob" title="GdaBlob"><span class="type">GdaBlob</span></a> which contains the data to write</p></td>
<td class="parameter_annotations"> </td>
</tr>
</tbody>
</table></div>
</div>
<div class="refsect3">
<a name="id-1.3.8.6.9.6.6"></a><h4>Returns</h4>
<p> TRUE on success</p>
<p></p>
</div>
</div>
</div>
<div class="refsect1">
<a name="GdaBlobOp.other_details"></a><h2>Types and Values</h2>
<div class="refsect2">
<a name="GdaBlobOp-struct"></a><h3>GdaBlobOp</h3>
<pre class="programlisting">typedef struct _GdaBlobOp GdaBlobOp;</pre>
</div>
</div>
</div>
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