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 211   <div class="section" id="working-with-data-on-the-server-in-an-atomic-fashion">
 212 <h1>Working with data on the server in an atomic fashion<a class="headerlink" href="#working-with-data-on-the-server-in-an-atomic-fashion" title="Permalink to this headline">¶</a></h1>
 213 <div class="section" id="synopsis">
 214 <span id="index-0"></span><h2>SYNOPSIS<a class="headerlink" href="#synopsis" title="Permalink to this headline">¶</a></h2>
 215 <p>#include &lt;libmemcached/memcached.h&gt;</p>
 216 <dl class="function">
 217 <dt id="_CPPv413memcached_casP12memcached_stPKc6size_tPKc6size_t6time_t8uint32_t8uint64_t">
 218 <span id="_CPPv313memcached_casP12memcached_stPKc6size_tPKc6size_t6time_t8uint32_t8uint64_t"></span><span id="_CPPv213memcached_casP12memcached_stPKc6size_tPKc6size_t6time_t8uint32_t8uint64_t"></span><span id="memcached_cas__memcached_stP.cCP.s.cCP.s.time_t.uint32_t.uint64_t"></span><a class="reference internal" href="memcached_return_t.html#_CPPv418memcached_return_t" title="memcached_return_t">memcached_return_t</a> <code class="sig-name descname">memcached_cas</code><span class="sig-paren">(</span><a class="reference internal" href="memcached_create.html#_CPPv412memcached_st" title="memcached_st">memcached_st</a> *<em>ptr</em>, <em class="property">const</em> char *<em>key</em>, size_t <em>key_length</em>, <em class="property">const</em> char *<em>value</em>, size_t <em>value_length</em>, time_t <em>expiration</em>, uint32_t <em>flags</em>, uint64_t <em>cas</em><span class="sig-paren">)</span><a class="headerlink" href="#_CPPv413memcached_casP12memcached_stPKc6size_tPKc6size_t6time_t8uint32_t8uint64_t" title="Permalink to this definition">¶</a><br /></dt>
 219 <dd></dd></dl>
 220
 221 <dl class="function">
 222 <dt id="_CPPv420memcached_cas_by_keyP12memcached_stPKc6size_tPKc6size_tPKc6size_t6time_t8uint32_t8uint64_t">
 223 <span id="_CPPv320memcached_cas_by_keyP12memcached_stPKc6size_tPKc6size_tPKc6size_t6time_t8uint32_t8uint64_t"></span><span id="_CPPv220memcached_cas_by_keyP12memcached_stPKc6size_tPKc6size_tPKc6size_t6time_t8uint32_t8uint64_t"></span><span id="memcached_cas_by_key__memcached_stP.cCP.s.cCP.s.cCP.s.time_t.uint32_t.uint64_t"></span><a class="reference internal" href="memcached_return_t.html#_CPPv418memcached_return_t" title="memcached_return_t">memcached_return_t</a> <code class="sig-name descname">memcached_cas_by_key</code><span class="sig-paren">(</span><a class="reference internal" href="memcached_create.html#_CPPv412memcached_st" title="memcached_st">memcached_st</a> *<em>ptr</em>, <em class="property">const</em> char *<em>group_key</em>, size_t <em>group_key_length</em>, <em class="property">const</em> char *<em>key</em>, size_t <em>key_length</em>, <em class="property">const</em> char *<em>value</em>, size_t <em>value_length</em>, time_t <em>expiration</em>, uint32_t <em>flags</em>, uint64_t <em>cas</em><span class="sig-paren">)</span><a class="headerlink" href="#_CPPv420memcached_cas_by_keyP12memcached_stPKc6size_tPKc6size_tPKc6size_t6time_t8uint32_t8uint64_t" title="Permalink to this definition">¶</a><br /></dt>
 224 <dd></dd></dl>
 225
 226 <p>Compile and link with -lmemcached</p>
 227 </div>
 228 <div class="section" id="description">
 229 <h2>DESCRIPTION<a class="headerlink" href="#description" title="Permalink to this headline">¶</a></h2>
 230 <p><a class="reference internal" href="#_CPPv413memcached_casP12memcached_stPKc6size_tPKc6size_t6time_t8uint32_t8uint64_t" title="memcached_cas"><code class="xref cpp cpp-func docutils literal notranslate"><span class="pre">memcached_cas()</span></code></a> overwrites data in the server as long as the “cas”
 231 value is still the same in the server. You can get the cas value of a result
 232 by calling <a class="reference internal" href="memcached_result_st.html#_CPPv420memcached_result_casPK19memcached_result_st" title="memcached_result_cas"><code class="xref cpp cpp-func docutils literal notranslate"><span class="pre">memcached_result_cas()</span></code></a> on a memcached_result_st(3)
 233 structure. At the point that this note was written cas is still buggy in memcached.
 234 Turning on tests for it in libmemcached(3) is optional. Please see
 235 <a class="reference internal" href="memcached_set.html#_CPPv413memcached_setP12memcached_stPKc6size_tPKc6size_t6time_t8uint32_t" title="memcached_set"><code class="xref cpp cpp-func docutils literal notranslate"><span class="pre">memcached_set()</span></code></a> for information on how to do this.</p>
 236 <p><a class="reference internal" href="#_CPPv420memcached_cas_by_keyP12memcached_stPKc6size_tPKc6size_tPKc6size_t6time_t8uint32_t8uint64_t" title="memcached_cas_by_key"><code class="xref cpp cpp-func docutils literal notranslate"><span class="pre">memcached_cas_by_key()</span></code></a> method behaves in a similar method as the non
 237 key methods. The difference is that it uses the group_key parameter
 238 to map objects to particular servers.</p>
 239 <p><a class="reference internal" href="#_CPPv413memcached_casP12memcached_stPKc6size_tPKc6size_t6time_t8uint32_t8uint64_t" title="memcached_cas"><code class="xref cpp cpp-func docutils literal notranslate"><span class="pre">memcached_cas()</span></code></a> is tested with the <a class="reference internal" href="memcached_behavior.html#_CPPv4N20memcached_behavior_t26MEMCACHED_BEHAVIOR_USE_UDPE" title="MEMCACHED_BEHAVIOR_USE_UDP"><code class="xref cpp cpp-any docutils literal notranslate"><span class="pre">MEMCACHED_BEHAVIOR_USE_UDP</span></code></a> behavior enabled. However, when using these operations with this behavior
 240 on, there are limits to the size of the payload being sent to the server.  The
 241 reason for these limits is that the Memcached Server does not allow
 242 multi-datagram requests and the current server implementation sets a datagram
 243 size to 1400 bytes. Due to protocol overhead, the actual limit of the user
 244 supplied data is less than 1400 bytes and depends on the protocol in use as,
 245 well as the operation being executed. When running with the binary protocol,
 246 <a class="reference internal" href="memcached_behavior.html#_CPPv4N20memcached_behavior_t34MEMCACHED_BEHAVIOR_BINARY_PROTOCOLE" title="MEMCACHED_BEHAVIOR_BINARY_PROTOCOL"><code class="xref cpp cpp-any docutils literal notranslate"><span class="pre">MEMCACHED_BEHAVIOR_BINARY_PROTOCOL</span></code></a>, the size of the key,value,
 247 flags and expiry combined may not exceed 1368 bytes. When running with the
 248 ASCII protocol, the exact limit fluctuates depending on which function is
 249 being executed and whether the function is a cas operation or not. For
 250 non-cas ASCII set operations, there are at least 1335 bytes available to
 251 split among the key, key_prefix, and value; for cas ASCII operations there
 252 are at least 1318 bytes available to split among the key, key_prefix and value. If the total size of the command, including overhead, exceeds 1400 bytes, a <a class="reference internal" href="memcached_return_t.html#_CPPv4N18memcached_return_t23MEMCACHED_WRITE_FAILUREE" title="MEMCACHED_WRITE_FAILURE"><code class="xref cpp cpp-any docutils literal notranslate"><span class="pre">MEMCACHED_WRITE_FAILURE</span></code></a> will be returned.</p>
 253 </div>
 254 <div class="section" id="return">
 255 <h2>RETURN<a class="headerlink" href="#return" title="Permalink to this headline">¶</a></h2>
 256 <p>All methods return a value of type <a class="reference internal" href="memcached_return_t.html#_CPPv418memcached_return_t" title="memcached_return_t"><code class="xref cpp cpp-type docutils literal notranslate"><span class="pre">memcached_return_t</span></code></a>.
 257 On success the value will be <a class="reference internal" href="memcached_return_t.html#_CPPv4N18memcached_return_t17MEMCACHED_SUCCESSE" title="MEMCACHED_SUCCESS"><code class="xref cpp cpp-any docutils literal notranslate"><span class="pre">MEMCACHED_SUCCESS</span></code></a>.
 258 Use <a class="reference internal" href="memcached_strerror.html#_CPPv418memcached_strerrorP12memcached_st18memcached_return_t" title="memcached_strerror"><code class="xref cpp cpp-func docutils literal notranslate"><span class="pre">memcached_strerror()</span></code></a> to translate this value to a printable
 259 string.</p>
 260 </div>
 261 <div class="section" id="see-also">
 262 <h2>SEE ALSO<a class="headerlink" href="#see-also" title="Permalink to this headline">¶</a></h2>
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