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 196   <div class="section" id="working-with-data-on-the-server-in-an-atomic-fashion">
 197 <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>
 198 <div class="section" id="synopsis">
 199 <h2>SYNOPSIS<a class="headerlink" href="#synopsis" title="Permalink to this headline">¶</a></h2>
 200 <dl class="simple">
 201 <dt>#include &lt;libmemcached/memcached.h&gt;</dt><dd><p>Compile and link with -lmemcached</p>
 202 </dd>
 203 </dl>
 204 <dl class="cpp function">
 205 <dt id="_CPPv413memcached_casP12memcached_stPKc6size_tPKc6size_t6time_t8uint32_t8uint64_t">
 206 <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>
 207 <dd></dd></dl>
 208
 209 <dl class="cpp function">
 210 <dt id="_CPPv420memcached_cas_by_keyP12memcached_stPKc6size_tPKc6size_tPKc6size_t6time_t8uint32_t8uint64_t">
 211 <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>
 212 <dd><dl class="field-list simple">
 213 <dt class="field-odd">Parameters</dt>
 214 <dd class="field-odd"><ul class="simple">
 215 <li><p><strong>ptr</strong> -- pointer to an initialized <a class="reference internal" href="memcached_create.html#_CPPv412memcached_st" title="memcached_st"><code class="xref cpp cpp-any docutils literal notranslate"><span class="pre">memcached_st</span></code></a> struct</p></li>
 216 <li><p><strong>group_key</strong> -- key namespace</p></li>
 217 <li><p><strong>group_key_length</strong> -- length of the <a class="reference internal" href="#_CPPv420memcached_cas_by_keyP12memcached_stPKc6size_tPKc6size_tPKc6size_t6time_t8uint32_t8uint64_t" title="memcached_cas_by_key::group_key"><code class="xref cpp cpp-any docutils literal notranslate"><span class="pre">group_key</span></code></a> without any trailing zero</p></li>
 218 <li><p><strong>key</strong> -- the key to check</p></li>
 219 <li><p><strong>key_length</strong> -- the length of the <a class="reference internal" href="#_CPPv420memcached_cas_by_keyP12memcached_stPKc6size_tPKc6size_tPKc6size_t6time_t8uint32_t8uint64_t" title="memcached_cas_by_key::key"><code class="xref cpp cpp-any docutils literal notranslate"><span class="pre">key</span></code></a> without any trailing zero</p></li>
 220 <li><p><strong>value</strong> -- the value to set</p></li>
 221 <li><p><strong>value_length</strong> -- the length of the <a class="reference internal" href="#_CPPv420memcached_cas_by_keyP12memcached_stPKc6size_tPKc6size_tPKc6size_t6time_t8uint32_t8uint64_t" title="memcached_cas_by_key::value"><code class="xref cpp cpp-any docutils literal notranslate"><span class="pre">value</span></code></a> without any trailing zero</p></li>
 222 <li><p><strong>expiration</strong> -- expiration time as unix timestamp or relative time in seconds</p></li>
 223 <li><p><strong>flags</strong> -- 16 bit flags</p></li>
 224 <li><p><strong>cas</strong> -- the <code class="docutils literal notranslate"><span class="pre">cas</span></code> value to compare</p></li>
 225 </ul>
 226 </dd>
 227 <dt class="field-even">Returns</dt>
 228 <dd class="field-even"><p><a class="reference internal" href="memcached_return_t.html#_CPPv418memcached_return_t" title="memcached_return_t"><code class="xref cpp cpp-any docutils literal notranslate"><span class="pre">memcached_return_t</span></code></a> indicating success</p>
 229 </dd>
 230 </dl>
 231 </dd></dl>
 232
 233 </div>
 234 <div class="section" id="description">
 235 <h2>DESCRIPTION<a class="headerlink" href="#description" title="Permalink to this headline">¶</a></h2>
 236 <p><a class="reference internal" href="#_CPPv413memcached_casP12memcached_stPKc6size_tPKc6size_t6time_t8uint32_t8uint64_t" title="memcached_cas"><code class="xref cpp cpp-any docutils literal notranslate"><span class="pre">memcached_cas()</span></code></a> overwrites data in the server as long as the <code class="docutils literal notranslate"><span class="pre">cas</span></code> value is
 237 still the same in the server. You can get the <code class="docutils literal notranslate"><span class="pre">cas</span></code> value of a result by
 238 calling <a class="reference internal" href="memcached_result_st.html#_CPPv420memcached_result_casPK19memcached_result_st" title="memcached_result_cas"><code class="xref cpp cpp-any docutils literal notranslate"><span class="pre">memcached_result_cas()</span></code></a> on a <a class="reference internal" href="memcached_result_st.html#_CPPv419memcached_result_st" title="memcached_result_st"><code class="xref cpp cpp-any docutils literal notranslate"><span class="pre">memcached_result_st</span></code></a> structure.</p>
 239 <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-any docutils literal notranslate"><span class="pre">memcached_cas_by_key()</span></code></a> method behaves in a similar way as the non key methods.
 240 The difference is that it uses the <code class="docutils literal notranslate"><span class="pre">group_key</span></code> parameter to map objects to
 241 particular servers.</p>
 242 <p><a class="reference internal" href="#_CPPv413memcached_casP12memcached_stPKc6size_tPKc6size_t6time_t8uint32_t8uint64_t" title="memcached_cas"><code class="xref cpp cpp-any 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
 243 enabled. However, when using these operations with this behavior on, there are
 244 limits to the size of the payload being sent to the server.  The reason for
 245 these limits is that the Memcached Server does not allow multi-datagram requests
 246 and the current server implementation sets a datagram size to 1400 bytes. Due to
 247 protocol overhead, the actual limit of the user supplied data is less than 1400
 248 bytes and depends on the protocol in use as, well as the operation being
 249 executed. When running with the binary protocol,
 250 <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, flags and
 251 expiry combined may not exceed 1368 bytes. When running with the ASCII protocol,
 252 the exact limit fluctuates depending on which function is being executed and
 253 whether the function is a cas operation or not. For non-cas ASCII set
 254 operations, there are at least 1335 bytes available to split among the key,
 255 key_prefix, and value; for cas ASCII operations there are at least 1318 bytes
 256 available to split among the key, key_prefix and value. If the total size of the
 257 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>
 258 will be returned.</p>
 259 </div>
 260 <div class="section" id="return-value">
 261 <h2>RETURN VALUE<a class="headerlink" href="#return-value" title="Permalink to this headline">¶</a></h2>
 262 <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-any docutils literal notranslate"><span class="pre">memcached_return_t</span></code></a>.
 263 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>.
 264 Use <a class="reference internal" href="memcached_strerror.html#_CPPv418memcached_strerrorP12memcached_st18memcached_return_t" title="memcached_strerror"><code class="xref cpp cpp-any docutils literal notranslate"><span class="pre">memcached_strerror()</span></code></a> to translate this value to a printable
 265 string.</p>
 266 </div>
 267 <div class="section" id="see-also">
 268 <h2>SEE ALSO<a class="headerlink" href="#see-also" title="Permalink to this headline">¶</a></h2>
 269 <ul class="simple">
 270 <li><p><em class="manpage"><a class="manpage reference external" href="https://linux.die.net/man/1/memcached">memcached(1)</a></em></p></li>
 271 <li><p><a class="reference internal" href="../libmemcached.html"><span class="doc">C/C++ Client Library for memcached</span></a></p></li>
 272 <li><p><a class="reference internal" href="memcached_set.html"><span class="doc">Storing data on the server</span></a></p></li>
 273 <li><p><a class="reference internal" href="memcached_append.html"><span class="doc">Appending or Prepending Data</span></a></p></li>
 274 <li><p><a class="reference internal" href="memcached_strerror.html"><span class="doc">Converting Error Codes to Messages</span></a></p></li>
 275 </ul>
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