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<div class="title">Packing and Unpacking Data </div> </div>
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<div class="textblock"><p>WiredTiger's data packing uses format strings similar to those specified in the Python struct module: <a href="http://docs.python.org/library/struct">http://docs.python.org/library/struct</a></p>
<p>The first character of the format string can be used to indicate the byte order, size and alignment of the packed data, according to the following table:</p>
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<th>Character</th><th>Byte order</th><th>Size</th><th>Alignment </th></tr>
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<td><code>.</code></td><td>big-endian</td><td>packed</td><td>none </td></tr>
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<td><code>></code></td><td>big-endian</td><td>standard</td><td>none </td></tr>
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<td><code><</code></td><td>little-endian</td><td>standard</td><td>none </td></tr>
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<td><code>@</code></td><td>native</td><td>native</td><td>native </td></tr>
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<p>If the first character is not one of these, '.' (big-endian, packed) is assumed: it naturally sorts in lexicographic order, and the packed format uses variable-sized encoding of values to reduce the data size.</p>
<p>Note: <b> little-endian format</b> not yet supported in WiredTiger. Only the default big-endian, packed format is currently supported.</p>
<p>The remaining characters in the format string specify the type of each field to be packed into or unpacked from a byte array. See <a class="el" href="schema.html#schema_column_types">Column types</a> for the list of supported types.</p>
<h1><a class="anchor" id="config_examples"></a>
Code samples</h1>
<p>The code below is taken from the complete example program <a class="el" href="ex_pack_8c-example.html">ex_pack.c</a>. It demonstrates how to pack three integer values into a buffer and then unpack them again.</p>
<div class="fragment"><div class="line"> <span class="keywordtype">size_t</span> size;</div><div class="line"> <span class="keywordtype">char</span> buf[50];</div><div class="line"></div><div class="line"> error_check(<a class="code" href="group__wt.html#ga156e7993d370495e1e52c29b2bb6b7d4">wiredtiger_struct_size</a>(session, &size, <span class="stringliteral">"iii"</span>, 42, 1000, -9));</div><div class="line"> <span class="keywordflow">if</span> (size > <span class="keyword">sizeof</span>(buf)) {</div><div class="line"> <span class="comment">/* Allocate a bigger buffer. */</span></div><div class="line"> }</div><div class="line"></div><div class="line"> error_check(<a class="code" href="group__wt.html#gab3d8a22e243360ece67baf33926d80fa">wiredtiger_struct_pack</a>(session, buf, size, <span class="stringliteral">"iii"</span>, 42, 1000, -9));</div><div class="line"></div><div class="line"> error_check(<a class="code" href="group__wt.html#ga7cdc8c688f2c15303188ed6999dcc1b4">wiredtiger_struct_unpack</a>(session, buf, size, <span class="stringliteral">"iii"</span>, &i, &j, &k));</div></div><!-- fragment --></div></div><!-- contents -->
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