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191 <div class="section" id="library-callbacks">
192 <h1>Library callbacks<a class="headerlink" href="#library-callbacks" title="Permalink to this headline"></a></h1>
193 <div class="section" id="synopsis">
194 <h2>SYNOPSIS<a class="headerlink" href="#synopsis" title="Permalink to this headline"></a></h2>
195 <dl class="docutils">
196 <dt>#include &lt;libmemcached/memcached.h&gt;</dt>
197 <dd>Compile and link with -lmemcached</dd>
198 </dl>
199 <dl class="function">
200 <dt id="_CPPv422memcached_callback_setP12memcached_st20memcached_callback_tPKv">
201 <span id="_CPPv322memcached_callback_setP12memcached_st20memcached_callback_tPKv"></span><span id="_CPPv222memcached_callback_setP12memcached_st20memcached_callback_tPKv"></span><span id="memcached_callback_set__memcached_stP.memcached_callback_t.voidCP"></span><a class="reference internal" href="memcached_return_t.html#_CPPv418memcached_return_t" title="memcached_return_t">memcached_return_t</a> <code class="descname">memcached_callback_set</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>, <a class="reference internal" href="#_CPPv420memcached_callback_t" title="memcached_callback_t">memcached_callback_t</a> <em>flag</em>, <em class="property">const</em> void *<em>data</em><span class="sig-paren">)</span><a class="headerlink" href="#_CPPv422memcached_callback_setP12memcached_st20memcached_callback_tPKv" title="Permalink to this definition"></a><br /></dt>
202 <dd><table class="docutils field-list" frame="void" rules="none">
203 <col class="field-name" />
204 <col class="field-body" />
205 <tbody valign="top">
206 <tr class="field-odd field"><th class="field-name">Parameters:</th><td class="field-body"><ul class="first simple">
207 <li><strong>ptr</strong> -- pointer to 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</li>
208 <li><strong>flag</strong> -- <a class="reference internal" href="#_CPPv420memcached_callback_t" title="memcached_callback_t"><code class="xref cpp cpp-any docutils literal notranslate"><span class="pre">memcached_callback_t</span></code></a> flag to set</li>
209 <li><strong>data</strong> -- data corresponding to <a class="reference internal" href="#_CPPv422memcached_callback_setP12memcached_st20memcached_callback_tPKv" title="memcached_callback_set::flag"><code class="xref cpp cpp-any docutils literal notranslate"><span class="pre">flag</span></code></a></li>
210 </ul>
211 </td>
212 </tr>
213 <tr class="field-even field"><th class="field-name">Returns:</th><td class="field-body"><p class="first last"><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>
214 </td>
215 </tr>
216 </tbody>
217 </table>
218 </dd></dl>
219
220 <dl class="function">
221 <dt id="_CPPv422memcached_callback_getP12memcached_st20memcached_callback_tP18memcached_return_t">
222 <span id="_CPPv322memcached_callback_getP12memcached_st20memcached_callback_tP18memcached_return_t"></span><span id="_CPPv222memcached_callback_getP12memcached_st20memcached_callback_tP18memcached_return_t"></span><span id="memcached_callback_get__memcached_stP.memcached_callback_t.memcached_return_tP"></span>void *<code class="descname">memcached_callback_get</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>, <a class="reference internal" href="#_CPPv420memcached_callback_t" title="memcached_callback_t">memcached_callback_t</a> <em>flag</em>, <a class="reference internal" href="memcached_return_t.html#_CPPv418memcached_return_t" title="memcached_return_t">memcached_return_t</a> *<em>error</em><span class="sig-paren">)</span><a class="headerlink" href="#_CPPv422memcached_callback_getP12memcached_st20memcached_callback_tP18memcached_return_t" title="Permalink to this definition"></a><br /></dt>
223 <dd><table class="docutils field-list" frame="void" rules="none">
224 <col class="field-name" />
225 <col class="field-body" />
226 <tbody valign="top">
227 <tr class="field-odd field"><th class="field-name">Parameters:</th><td class="field-body"><ul class="first simple">
228 <li><strong>ptr</strong> -- pointer to 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</li>
229 <li><strong>flag</strong> -- <a class="reference internal" href="#_CPPv420memcached_callback_t" title="memcached_callback_t"><code class="xref cpp cpp-any docutils literal notranslate"><span class="pre">memcached_callback_t</span></code></a> flag to query</li>
230 <li><strong>error</strong> -- pointer to <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</li>
231 </ul>
232 </td>
233 </tr>
234 <tr class="field-even field"><th class="field-name">Returns:</th><td class="field-body"><p class="first last">the <code class="xref cpp cpp-any docutils literal notranslate"><span class="pre">data</span></code> previously set</p>
235 </td>
236 </tr>
237 </tbody>
238 </table>
239 </dd></dl>
240
241 <dl class="type">
242 <dt id="c.memcached_callback_t">
243 enum <a class="reference internal" href="#c.memcached_callback_t" title="memcached_callback_t">memcached_callback_t</a> <code class="descname">memcached_callback_t</code><a class="headerlink" href="#c.memcached_callback_t" title="Permalink to this definition"></a></dt>
244 <dd></dd></dl>
245
246 <dl class="enum">
247 <dt id="_CPPv420memcached_callback_t">
248 <span id="_CPPv320memcached_callback_t"></span><span id="_CPPv220memcached_callback_t"></span><em class="property">enum </em><code class="descname">memcached_callback_t</code><a class="headerlink" href="#_CPPv420memcached_callback_t" title="Permalink to this definition"></a><br /></dt>
249 <dd><dl class="enumerator">
250 <dt id="_CPPv4N20memcached_callback_t35MEMCACHED_CALLBACK_CLEANUP_FUNCTIONE">
251 <span id="_CPPv3N20memcached_callback_t35MEMCACHED_CALLBACK_CLEANUP_FUNCTIONE"></span><span id="_CPPv2N20memcached_callback_t35MEMCACHED_CALLBACK_CLEANUP_FUNCTIONE"></span><em class="property">enumerator </em><code class="descname">MEMCACHED_CALLBACK_CLEANUP_FUNCTION</code><a class="headerlink" href="#_CPPv4N20memcached_callback_t35MEMCACHED_CALLBACK_CLEANUP_FUNCTIONE" title="Permalink to this definition"></a><br /></dt>
252 <dd><p>When <a class="reference internal" href="memcached_create.html#_CPPv414memcached_freeP12memcached_st" title="memcached_free"><code class="xref cpp cpp-any docutils literal notranslate"><span class="pre">memcached_free()</span></code></a> or <code class="xref cpp cpp-any docutils literal notranslate"><span class="pre">memcached_reset</span></code> is called this function
253 will be executed. At the point of its execution all connections are closed.</p>
254 <p>Its signature is:</p>
255 <dl class="type">
256 <dt id="_CPPv4N20memcached_callback_t35MEMCACHED_CALLBACK_CLEANUP_FUNCTION20memcached_cleanup_fnE">
257 <span id="_CPPv3N20memcached_callback_t35MEMCACHED_CALLBACK_CLEANUP_FUNCTION20memcached_cleanup_fnE"></span><span id="_CPPv2N20memcached_callback_t35MEMCACHED_CALLBACK_CLEANUP_FUNCTION20memcached_cleanup_fnE"></span><span id="memcached_callback_t::MEMCACHED_CALLBACK_CLEANUP_FUNCTION::memcached_cleanup_fn"></span><em class="property">typedef </em><a class="reference internal" href="memcached_return_t.html#_CPPv418memcached_return_t" title="memcached_return_t">memcached_return_t</a> (*<code class="descname">memcached_cleanup_fn</code>)<span class="sig-paren">(</span><em class="property">const</em> <a class="reference internal" href="memcached_create.html#_CPPv412memcached_st" title="memcached_st">memcached_st</a> *ptr<span class="sig-paren">)</span><a class="headerlink" href="#_CPPv4N20memcached_callback_t35MEMCACHED_CALLBACK_CLEANUP_FUNCTION20memcached_cleanup_fnE" title="Permalink to this definition"></a><br /></dt>
258 <dd></dd></dl>
259
260 </dd></dl>
261
262 <dl class="enumerator">
263 <dt id="_CPPv4N20memcached_callback_t33MEMCACHED_CALLBACK_CLONE_FUNCTIONE">
264 <span id="_CPPv3N20memcached_callback_t33MEMCACHED_CALLBACK_CLONE_FUNCTIONE"></span><span id="_CPPv2N20memcached_callback_t33MEMCACHED_CALLBACK_CLONE_FUNCTIONE"></span><em class="property">enumerator </em><code class="descname">MEMCACHED_CALLBACK_CLONE_FUNCTION</code><a class="headerlink" href="#_CPPv4N20memcached_callback_t33MEMCACHED_CALLBACK_CLONE_FUNCTIONE" title="Permalink to this definition"></a><br /></dt>
265 <dd><p>When <a class="reference internal" href="memcached_create.html#_CPPv415memcached_cloneP12memcached_stP12memcached_st" title="memcached_clone"><code class="xref cpp cpp-any docutils literal notranslate"><span class="pre">memcached_clone()</span></code></a> is called this function will be executed.</p>
266 <p>Its signature is:</p>
267 <dl class="type">
268 <dt id="_CPPv4N20memcached_callback_t33MEMCACHED_CALLBACK_CLONE_FUNCTION18memcached_clone_fnE">
269 <span id="_CPPv3N20memcached_callback_t33MEMCACHED_CALLBACK_CLONE_FUNCTION18memcached_clone_fnE"></span><span id="_CPPv2N20memcached_callback_t33MEMCACHED_CALLBACK_CLONE_FUNCTION18memcached_clone_fnE"></span><span id="memcached_callback_t::MEMCACHED_CALLBACK_CLONE_FUNCTION::memcached_clone_fn"></span><em class="property">typedef </em><a class="reference internal" href="memcached_return_t.html#_CPPv418memcached_return_t" title="memcached_return_t">memcached_return_t</a> (*<code class="descname">memcached_clone_fn</code>)<span class="sig-paren">(</span><a class="reference internal" href="memcached_create.html#_CPPv412memcached_st" title="memcached_st">memcached_st</a> *destination, <em class="property">const</em> <a class="reference internal" href="memcached_create.html#_CPPv412memcached_st" title="memcached_st">memcached_st</a> *source<span class="sig-paren">)</span><a class="headerlink" href="#_CPPv4N20memcached_callback_t33MEMCACHED_CALLBACK_CLONE_FUNCTION18memcached_clone_fnE" title="Permalink to this definition"></a><br /></dt>
270 <dd></dd></dl>
271
272 </dd></dl>
273
274 <dl class="enumerator">
275 <dt id="_CPPv4N20memcached_callback_t29MEMCACHED_CALLBACK_PREFIX_KEYE">
276 <span id="_CPPv3N20memcached_callback_t29MEMCACHED_CALLBACK_PREFIX_KEYE"></span><span id="_CPPv2N20memcached_callback_t29MEMCACHED_CALLBACK_PREFIX_KEYE"></span><em class="property">enumerator </em><code class="descname">MEMCACHED_CALLBACK_PREFIX_KEY</code><a class="headerlink" href="#_CPPv4N20memcached_callback_t29MEMCACHED_CALLBACK_PREFIX_KEYE" title="Permalink to this definition"></a><br /></dt>
277 <dd><p>See <a class="reference internal" href="#_CPPv4N20memcached_callback_t28MEMCACHED_CALLBACK_NAMESPACEE" title="memcached_callback_t::MEMCACHED_CALLBACK_NAMESPACE"><code class="xref cpp cpp-any docutils literal notranslate"><span class="pre">MEMCACHED_CALLBACK_NAMESPACE</span></code></a>.</p>
278 </dd></dl>
279
280 <dl class="enumerator">
281 <dt id="_CPPv4N20memcached_callback_t28MEMCACHED_CALLBACK_NAMESPACEE">
282 <span id="_CPPv3N20memcached_callback_t28MEMCACHED_CALLBACK_NAMESPACEE"></span><span id="_CPPv2N20memcached_callback_t28MEMCACHED_CALLBACK_NAMESPACEE"></span><em class="property">enumerator </em><code class="descname">MEMCACHED_CALLBACK_NAMESPACE</code><a class="headerlink" href="#_CPPv4N20memcached_callback_t28MEMCACHED_CALLBACK_NAMESPACEE" title="Permalink to this definition"></a><br /></dt>
283 <dd><p>You can set a value which will be used to create a domain for your keys.
284 The value specified here will be prefixed to each of your keys. The
285 value can not be greater then <a class="reference internal" href="constants.html#c.MEMCACHED_MAX_NAMESPACE" title="MEMCACHED_MAX_NAMESPACE"><code class="xref c c-macro docutils literal notranslate"><span class="pre">MEMCACHED_MAX_NAMESPACE</span></code></a> - 1 and
286 will reduce <a class="reference internal" href="constants.html#c.MEMCACHED_MAX_KEY" title="MEMCACHED_MAX_KEY"><code class="xref c c-macro docutils literal notranslate"><span class="pre">MEMCACHED_MAX_KEY</span></code></a> by the value of your key.</p>
287 <p>The prefix key is only applied to the primary key, not the master key.
288 <a class="reference internal" href="memcached_return_t.html#_CPPv4N18memcached_return_t17MEMCACHED_FAILUREE" title="MEMCACHED_FAILURE"><code class="xref cpp cpp-any docutils literal notranslate"><span class="pre">MEMCACHED_FAILURE</span></code></a> will be returned if no key is set. In the case of a
289 key which is too long, <a class="reference internal" href="memcached_return_t.html#_CPPv4N18memcached_return_t26MEMCACHED_BAD_KEY_PROVIDEDE" title="MEMCACHED_BAD_KEY_PROVIDED"><code class="xref cpp cpp-any docutils literal notranslate"><span class="pre">MEMCACHED_BAD_KEY_PROVIDED</span></code></a> will be returned.</p>
290 <p>If you set a value with the value being NULL then the prefix key is
291 disabled.</p>
292 </dd></dl>
293
294 <dl class="enumerator">
295 <dt id="_CPPv4N20memcached_callback_t28MEMCACHED_CALLBACK_USER_DATAE">
296 <span id="_CPPv3N20memcached_callback_t28MEMCACHED_CALLBACK_USER_DATAE"></span><span id="_CPPv2N20memcached_callback_t28MEMCACHED_CALLBACK_USER_DATAE"></span><em class="property">enumerator </em><code class="descname">MEMCACHED_CALLBACK_USER_DATA</code><a class="headerlink" href="#_CPPv4N20memcached_callback_t28MEMCACHED_CALLBACK_USER_DATAE" title="Permalink to this definition"></a><br /></dt>
297 <dd><p>This allows you to store a pointer to a specific piece of data. This can
298 be retrieved from inside of <a class="reference internal" href="memcached_get.html#_CPPv423memcached_fetch_executeP12memcached_stP20memcached_execute_fnPv8uint32_t" title="memcached_fetch_execute"><code class="xref cpp cpp-any docutils literal notranslate"><span class="pre">memcached_fetch_execute()</span></code></a>. Cloning a
299 <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> will copy the pointer to the clone.</p>
300 </dd></dl>
301
302 <dl class="enumerator">
303 <dt id="_CPPv4N20memcached_callback_t34MEMCACHED_CALLBACK_MALLOC_FUNCTIONE">
304 <span id="_CPPv3N20memcached_callback_t34MEMCACHED_CALLBACK_MALLOC_FUNCTIONE"></span><span id="_CPPv2N20memcached_callback_t34MEMCACHED_CALLBACK_MALLOC_FUNCTIONE"></span><em class="property">enumerator </em><code class="descname">MEMCACHED_CALLBACK_MALLOC_FUNCTION</code><a class="headerlink" href="#_CPPv4N20memcached_callback_t34MEMCACHED_CALLBACK_MALLOC_FUNCTIONE" title="Permalink to this definition"></a><br /></dt>
305 <dd><div class="deprecated">
306 <p><span class="versionmodified">Deprecated since version &lt;0.32: </span>Use <a class="reference internal" href="memcached_memory_allocators.html#_CPPv431memcached_set_memory_allocatorsP12memcached_st19memcached_malloc_fn17memcached_free_fn20memcached_realloc_fn19memcached_calloc_fnPv" title="memcached_set_memory_allocators"><code class="xref cpp cpp-any docutils literal notranslate"><span class="pre">memcached_set_memory_allocators()</span></code></a> instead.</p>
307 </div>
308 </dd></dl>
309
310 <dl class="enumerator">
311 <dt id="_CPPv4N20memcached_callback_t35MEMCACHED_CALLBACK_REALLOC_FUNCTIONE">
312 <span id="_CPPv3N20memcached_callback_t35MEMCACHED_CALLBACK_REALLOC_FUNCTIONE"></span><span id="_CPPv2N20memcached_callback_t35MEMCACHED_CALLBACK_REALLOC_FUNCTIONE"></span><em class="property">enumerator </em><code class="descname">MEMCACHED_CALLBACK_REALLOC_FUNCTION</code><a class="headerlink" href="#_CPPv4N20memcached_callback_t35MEMCACHED_CALLBACK_REALLOC_FUNCTIONE" title="Permalink to this definition"></a><br /></dt>
313 <dd><div class="deprecated">
314 <p><span class="versionmodified">Deprecated since version &lt;0.32: </span>Use <a class="reference internal" href="memcached_memory_allocators.html#_CPPv431memcached_set_memory_allocatorsP12memcached_st19memcached_malloc_fn17memcached_free_fn20memcached_realloc_fn19memcached_calloc_fnPv" title="memcached_set_memory_allocators"><code class="xref cpp cpp-any docutils literal notranslate"><span class="pre">memcached_set_memory_allocators()</span></code></a> instead.</p>
315 </div>
316 </dd></dl>
317
318 <dl class="enumerator">
319 <dt id="_CPPv4N20memcached_callback_t32MEMCACHED_CALLBACK_FREE_FUNCTIONE">
320 <span id="_CPPv3N20memcached_callback_t32MEMCACHED_CALLBACK_FREE_FUNCTIONE"></span><span id="_CPPv2N20memcached_callback_t32MEMCACHED_CALLBACK_FREE_FUNCTIONE"></span><em class="property">enumerator </em><code class="descname">MEMCACHED_CALLBACK_FREE_FUNCTION</code><a class="headerlink" href="#_CPPv4N20memcached_callback_t32MEMCACHED_CALLBACK_FREE_FUNCTIONE" title="Permalink to this definition"></a><br /></dt>
321 <dd><div class="deprecated">
322 <p><span class="versionmodified">Deprecated since version &lt;0.32: </span>Use <a class="reference internal" href="memcached_memory_allocators.html#_CPPv431memcached_set_memory_allocatorsP12memcached_st19memcached_malloc_fn17memcached_free_fn20memcached_realloc_fn19memcached_calloc_fnPv" title="memcached_set_memory_allocators"><code class="xref cpp cpp-any docutils literal notranslate"><span class="pre">memcached_set_memory_allocators()</span></code></a> instead.</p>
323 </div>
324 </dd></dl>
325
326 <dl class="enumerator">
327 <dt id="_CPPv4N20memcached_callback_t30MEMCACHED_CALLBACK_GET_FAILUREE">
328 <span id="_CPPv3N20memcached_callback_t30MEMCACHED_CALLBACK_GET_FAILUREE"></span><span id="_CPPv2N20memcached_callback_t30MEMCACHED_CALLBACK_GET_FAILUREE"></span><em class="property">enumerator </em><code class="descname">MEMCACHED_CALLBACK_GET_FAILURE</code><a class="headerlink" href="#_CPPv4N20memcached_callback_t30MEMCACHED_CALLBACK_GET_FAILUREE" title="Permalink to this definition"></a><br /></dt>
329 <dd><p>This function implements the read through cache behavior. On failure of
330 retrieval this callback will be called.</p>
331 <p>You are responsible for populating the result object provided. This
332 result object will then be stored in the server and returned to the
333 calling process.</p>
334 <p>You must clone the <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> in order to make use of it. The value
335 will be stored only if you return <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> or
336 <a class="reference internal" href="memcached_return_t.html#_CPPv4N18memcached_return_t18MEMCACHED_BUFFEREDE" title="MEMCACHED_BUFFERED"><code class="xref cpp cpp-any docutils literal notranslate"><span class="pre">MEMCACHED_BUFFERED</span></code></a>. Returning <a class="reference internal" href="memcached_return_t.html#_CPPv4N18memcached_return_t18MEMCACHED_BUFFEREDE" title="MEMCACHED_BUFFERED"><code class="xref cpp cpp-any docutils literal notranslate"><span class="pre">MEMCACHED_BUFFERED</span></code></a> will cause the
337 object to be buffered and not sent immediately (if this is the default
338 behavior based on your connection setup this will happen automatically).</p>
339 <p>The prototype for this is:</p>
340 <dl class="type">
341 <dt id="_CPPv4N20memcached_callback_t30MEMCACHED_CALLBACK_GET_FAILURE21memcached_trigger_keyE">
342 <span id="_CPPv3N20memcached_callback_t30MEMCACHED_CALLBACK_GET_FAILURE21memcached_trigger_keyE"></span><span id="_CPPv2N20memcached_callback_t30MEMCACHED_CALLBACK_GET_FAILURE21memcached_trigger_keyE"></span><span id="memcached_callback_t::MEMCACHED_CALLBACK_GET_FAILURE::memcached_trigger_key"></span><em class="property">typedef </em><a class="reference internal" href="memcached_return_t.html#_CPPv418memcached_return_t" title="memcached_return_t">memcached_return_t</a> (*<code class="descname">memcached_trigger_key</code>)<span class="sig-paren">(</span><a class="reference internal" href="memcached_create.html#_CPPv412memcached_st" title="memcached_st">memcached_st</a> *ptr, char *key, size_t key_length, <a class="reference internal" href="memcached_result_st.html#_CPPv419memcached_result_st" title="memcached_result_st">memcached_result_st</a> *result<span class="sig-paren">)</span><a class="headerlink" href="#_CPPv4N20memcached_callback_t30MEMCACHED_CALLBACK_GET_FAILURE21memcached_trigger_keyE" title="Permalink to this definition"></a><br /></dt>
343 <dd></dd></dl>
344
345 </dd></dl>
346
347 <dl class="enumerator">
348 <dt id="_CPPv4N20memcached_callback_t33MEMCACHED_CALLBACK_DELETE_TRIGGERE">
349 <span id="_CPPv3N20memcached_callback_t33MEMCACHED_CALLBACK_DELETE_TRIGGERE"></span><span id="_CPPv2N20memcached_callback_t33MEMCACHED_CALLBACK_DELETE_TRIGGERE"></span><em class="property">enumerator </em><code class="descname">MEMCACHED_CALLBACK_DELETE_TRIGGER</code><a class="headerlink" href="#_CPPv4N20memcached_callback_t33MEMCACHED_CALLBACK_DELETE_TRIGGERE" title="Permalink to this definition"></a><br /></dt>
350 <dd><p>This function implements a trigger upon successful deletion of a key.
351 The <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> structure will need to be cloned in order to make use
352 of it.</p>
353 <p>The prototype for this is:</p>
354 <dl class="type">
355 <dt id="_CPPv4N20memcached_callback_t33MEMCACHED_CALLBACK_DELETE_TRIGGER28memcached_trigger_delete_keyE">
356 <span id="_CPPv3N20memcached_callback_t33MEMCACHED_CALLBACK_DELETE_TRIGGER28memcached_trigger_delete_keyE"></span><span id="_CPPv2N20memcached_callback_t33MEMCACHED_CALLBACK_DELETE_TRIGGER28memcached_trigger_delete_keyE"></span><span id="memcached_callback_t::MEMCACHED_CALLBACK_DELETE_TRIGGER::memcached_trigger_delete_key"></span><em class="property">typedef </em><a class="reference internal" href="memcached_return_t.html#_CPPv418memcached_return_t" title="memcached_return_t">memcached_return_t</a> (*<code class="descname">memcached_trigger_delete_key</code>)<span class="sig-paren">(</span><a class="reference internal" href="memcached_create.html#_CPPv412memcached_st" title="memcached_st">memcached_st</a> *ptr, char *key, size_t key_length<span class="sig-paren">)</span><a class="headerlink" href="#_CPPv4N20memcached_callback_t33MEMCACHED_CALLBACK_DELETE_TRIGGER28memcached_trigger_delete_keyE" title="Permalink to this definition"></a><br /></dt>
357 <dd></dd></dl>
358
359 </dd></dl>
360
361 </dd></dl>
362
363 </div>
364 <div class="section" id="description">
365 <h2>DESCRIPTION<a class="headerlink" href="#description" title="Permalink to this headline"></a></h2>
366 <p><code class="xref cpp cpp-any docutils literal notranslate"><span class="pre">libmemcached</span></code> can have callbacks set key execution points. These either provide
367 function calls at points in the code, or return pointers to structures for
368 particular usages.</p>
369 <p><a class="reference internal" href="#_CPPv422memcached_callback_getP12memcached_st20memcached_callback_tP18memcached_return_t" title="memcached_callback_get"><code class="xref cpp cpp-any docutils literal notranslate"><span class="pre">memcached_callback_get()</span></code></a> takes a callback flag and returns the structure or
370 function set by <a class="reference internal" href="#_CPPv422memcached_callback_setP12memcached_st20memcached_callback_tPKv" title="memcached_callback_set"><code class="xref cpp cpp-any docutils literal notranslate"><span class="pre">memcached_callback_set()</span></code></a>.</p>
371 <p><a class="reference internal" href="#_CPPv422memcached_callback_setP12memcached_st20memcached_callback_tPKv" title="memcached_callback_set"><code class="xref cpp cpp-any docutils literal notranslate"><span class="pre">memcached_callback_set()</span></code></a> changes the function/structure assigned by a callback
372 flag. No connections are reset.</p>
373 <p>You can use <a class="reference internal" href="#_CPPv4N20memcached_callback_t28MEMCACHED_CALLBACK_USER_DATAE" title="MEMCACHED_CALLBACK_USER_DATA"><code class="xref cpp cpp-any docutils literal notranslate"><span class="pre">MEMCACHED_CALLBACK_USER_DATA</span></code></a> to provide custom context if required
374 for any of the callbacks.</p>
375 </div>
376 <div class="section" id="return-value">
377 <h2>RETURN VALUE<a class="headerlink" href="#return-value" title="Permalink to this headline"></a></h2>
378 <p><a class="reference internal" href="#_CPPv422memcached_callback_getP12memcached_st20memcached_callback_tP18memcached_return_t" title="memcached_callback_get"><code class="xref cpp cpp-any docutils literal notranslate"><span class="pre">memcached_callback_get()</span></code></a> returns the function or structure that was provided.
379 Upon error, nothing is set, NULL is returned, and the <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>
380 argument is set to <a class="reference internal" href="memcached_return_t.html#_CPPv4N18memcached_return_t17MEMCACHED_FAILUREE" title="MEMCACHED_FAILURE"><code class="xref cpp cpp-any docutils literal notranslate"><span class="pre">MEMCACHED_FAILURE</span></code></a>.</p>
381 <p><a class="reference internal" href="#_CPPv422memcached_callback_setP12memcached_st20memcached_callback_tPKv" title="memcached_callback_set"><code class="xref cpp cpp-any docutils literal notranslate"><span class="pre">memcached_callback_set()</span></code></a> returns <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> upon successful setting,
382 otherwise <a class="reference internal" href="memcached_return_t.html#_CPPv4N18memcached_return_t17MEMCACHED_FAILUREE" title="MEMCACHED_FAILURE"><code class="xref cpp cpp-any docutils literal notranslate"><span class="pre">MEMCACHED_FAILURE</span></code></a> on error.</p>
383 </div>
384 <div class="section" id="see-also">
385 <h2>SEE ALSO<a class="headerlink" href="#see-also" title="Permalink to this headline"></a></h2>
386 <ul class="simple">
387 <li><em class="manpage"><a class="manpage reference external" href="https://linux.die.net/man/1/memcached">memcached(1)</a></em></li>
388 <li><a class="reference internal" href="../libmemcached.html"><span class="doc">C/C++ Client Library for memcached</span></a></li>
389 <li><a class="reference internal" href="memcached_strerror.html"><span class="doc">Converting Error Codes to Messages</span></a></li>
390 </ul>
391 </div>
392 </div>
393
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