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 198
 199   <div class="section" id="setting-callbacks">
 200 <h1>Setting callbacks<a class="headerlink" href="#setting-callbacks" title="Permalink to this headline">¶</a></h1>
 201 <p>Get and set a callback</p>
 202 <div class="section" id="synopsis">
 203 <span id="index-0"></span><h2>SYNOPSIS<a class="headerlink" href="#synopsis" title="Permalink to this headline">¶</a></h2>
 204 <dl class="simple">
 205 <dt>#include &lt;libmemcached/memcached.h&gt;</dt><dd><p>Compile and link with -lmemcached</p>
 206 </dd>
 207 </dl>
 208 <dl class="function">
 209 <dt id="_CPPv422memcached_callback_setP12memcached_st20memcached_callback_tPKv">
 210 <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="sig-name 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>
 211 <dd></dd></dl>
 212
 213 <dl class="function">
 214 <dt id="_CPPv422memcached_callback_getP12memcached_st20memcached_callback_tP18memcached_return_t">
 215 <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="sig-name 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>
 216 <dd></dd></dl>
 217
 218 <dl class="type">
 219 <dt id="c.memcached_callback_t">
 220 enum <a class="reference internal" href="#c.memcached_callback_t" title="memcached_callback_t">memcached_callback_t</a> <code class="sig-name descname">memcached_callback_t</code><a class="headerlink" href="#c.memcached_callback_t" title="Permalink to this definition">¶</a></dt>
 221 <dd></dd></dl>
 222
 223 <dl class="enum">
 224 <dt id="_CPPv420memcached_callback_t">
 225 <span id="_CPPv320memcached_callback_t"></span><span id="_CPPv220memcached_callback_t"></span><em class="property">enum </em><code class="sig-name descname">memcached_callback_t</code><a class="headerlink" href="#_CPPv420memcached_callback_t" title="Permalink to this definition">¶</a><br /></dt>
 226 <dd><dl class="enumerator">
 227 <dt id="_CPPv4N20memcached_callback_t35MEMCACHED_CALLBACK_CLEANUP_FUNCTIONE">
 228 <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="sig-name descname">MEMCACHED_CALLBACK_CLEANUP_FUNCTION</code><a class="headerlink" href="#_CPPv4N20memcached_callback_t35MEMCACHED_CALLBACK_CLEANUP_FUNCTIONE" title="Permalink to this definition">¶</a><br /></dt>
 229 <dd><p>When <a class="reference internal" href="memcached_delete.html#_CPPv416memcached_deleteP12memcached_stPKc6size_t6time_t" title="memcached_delete"><code class="xref cpp cpp-func docutils literal notranslate"><span class="pre">memcached_delete()</span></code></a> is called this function will be executed. At
 230 the point of its execution all connections are closed.</p>
 231 </dd></dl>
 232
 233 <dl class="enumerator">
 234 <dt id="_CPPv4N20memcached_callback_t33MEMCACHED_CALLBACK_CLONE_FUNCTIONE">
 235 <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="sig-name descname">MEMCACHED_CALLBACK_CLONE_FUNCTION</code><a class="headerlink" href="#_CPPv4N20memcached_callback_t33MEMCACHED_CALLBACK_CLONE_FUNCTIONE" title="Permalink to this definition">¶</a><br /></dt>
 236 <dd><p>When <a class="reference internal" href="memcached_delete.html#_CPPv416memcached_deleteP12memcached_stPKc6size_t6time_t" title="memcached_delete"><code class="xref cpp cpp-func docutils literal notranslate"><span class="pre">memcached_delete()</span></code></a> is called this function will be executed.
 237 At the point of its execution all connections are closed.</p>
 238 </dd></dl>
 239
 240 <dl class="enumerator">
 241 <dt id="_CPPv4N20memcached_callback_t29MEMCACHED_CALLBACK_PREFIX_KEYE">
 242 <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="sig-name descname">MEMCACHED_CALLBACK_PREFIX_KEY</code><a class="headerlink" href="#_CPPv4N20memcached_callback_t29MEMCACHED_CALLBACK_PREFIX_KEYE" title="Permalink to this definition">¶</a><br /></dt>
 243 <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>
 244 </dd></dl>
 245
 246 <dl class="enumerator">
 247 <dt id="_CPPv4N20memcached_callback_t28MEMCACHED_CALLBACK_NAMESPACEE">
 248 <span id="_CPPv3N20memcached_callback_t28MEMCACHED_CALLBACK_NAMESPACEE"></span><span id="_CPPv2N20memcached_callback_t28MEMCACHED_CALLBACK_NAMESPACEE"></span><em class="property">enumerator </em><code class="sig-name descname">MEMCACHED_CALLBACK_NAMESPACE</code><a class="headerlink" href="#_CPPv4N20memcached_callback_t28MEMCACHED_CALLBACK_NAMESPACEE" title="Permalink to this definition">¶</a><br /></dt>
 249 <dd><p>You can set a value which will be used to create a domain for your keys.
 250 The value specified here will be prefixed to each of your keys. The value can
 251 not be greater then <code class="xref cpp cpp-any docutils literal notranslate"><span class="pre">MEMCACHED_PREFIX_KEY_MAX_SIZE</span></code> - 1 and will
 252 reduce <code class="xref cpp cpp-any docutils literal notranslate"><span class="pre">MEMCACHED_MAX_KEY</span></code> by the value of your key.</p>
 253 <p>The prefix key is only applied to the primary key, not the master key.
 254 <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
 255 a 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>
 256 <p>If you set a value with the value being NULL then the prefix key is disabled.</p>
 257 </dd></dl>
 258
 259 <dl class="enumerator">
 260 <dt id="_CPPv4N20memcached_callback_t28MEMCACHED_CALLBACK_USER_DATAE">
 261 <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="sig-name descname">MEMCACHED_CALLBACK_USER_DATA</code><a class="headerlink" href="#_CPPv4N20memcached_callback_t28MEMCACHED_CALLBACK_USER_DATAE" title="Permalink to this definition">¶</a><br /></dt>
 262 <dd><p>This allows you to store a pointer to a specific piece of data. This can be
 263 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-func docutils literal notranslate"><span class="pre">memcached_fetch_execute()</span></code></a>. Cloning a
 264 <a class="reference internal" href="memcached_create.html#_CPPv412memcached_st" title="memcached_st"><code class="xref cpp cpp-type docutils literal notranslate"><span class="pre">memcached_st</span></code></a> will copy the pointer to the clone.</p>
 265 </dd></dl>
 266
 267 <dl class="enumerator">
 268 <dt id="_CPPv4N20memcached_callback_t34MEMCACHED_CALLBACK_MALLOC_FUNCTIONE">
 269 <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="sig-name descname">MEMCACHED_CALLBACK_MALLOC_FUNCTION</code><a class="headerlink" href="#_CPPv4N20memcached_callback_t34MEMCACHED_CALLBACK_MALLOC_FUNCTIONE" title="Permalink to this definition">¶</a><br /></dt>
 270 <dd><div class="deprecated">
 271 <p><span class="versionmodified deprecated">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-type docutils literal notranslate"><span class="pre">memcached_set_memory_allocators</span></code></a> instead.</p>
 272 </div>
 273 </dd></dl>
 274
 275 <dl class="enumerator">
 276 <dt id="_CPPv4N20memcached_callback_t35MEMCACHED_CALLBACK_REALLOC_FUNCTIONE">
 277 <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="sig-name descname">MEMCACHED_CALLBACK_REALLOC_FUNCTION</code><a class="headerlink" href="#_CPPv4N20memcached_callback_t35MEMCACHED_CALLBACK_REALLOC_FUNCTIONE" title="Permalink to this definition">¶</a><br /></dt>
 278 <dd><div class="deprecated">
 279 <p><span class="versionmodified deprecated">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-type docutils literal notranslate"><span class="pre">memcached_set_memory_allocators</span></code></a> instead.</p>
 280 </div>
 281 </dd></dl>
 282
 283 <dl class="enumerator">
 284 <dt id="_CPPv4N20memcached_callback_t32MEMCACHED_CALLBACK_FREE_FUNCTIONE">
 285 <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="sig-name descname">MEMCACHED_CALLBACK_FREE_FUNCTION</code><a class="headerlink" href="#_CPPv4N20memcached_callback_t32MEMCACHED_CALLBACK_FREE_FUNCTIONE" title="Permalink to this definition">¶</a><br /></dt>
 286 <dd><div class="deprecated">
 287 <p><span class="versionmodified deprecated">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-type docutils literal notranslate"><span class="pre">memcached_set_memory_allocators</span></code></a> instead.</p>
 288 </div>
 289 </dd></dl>
 290
 291 <dl class="enumerator">
 292 <dt id="_CPPv4N20memcached_callback_t30MEMCACHED_CALLBACK_GET_FAILUREE">
 293 <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="sig-name descname">MEMCACHED_CALLBACK_GET_FAILURE</code><a class="headerlink" href="#_CPPv4N20memcached_callback_t30MEMCACHED_CALLBACK_GET_FAILUREE" title="Permalink to this definition">¶</a><br /></dt>
 294 <dd><p>This function implements the read through cache behavior. On failure of retrieval this callback will be called.</p>
 295 <p>You are responsible for populating the result object provided. This result object will then be stored in the server and returned to the calling process.</p>
 296 <p>You must clone the <a class="reference internal" href="memcached_create.html#_CPPv412memcached_st" title="memcached_st"><code class="xref cpp cpp-type docutils literal notranslate"><span class="pre">memcached_st</span></code></a> in order to
 297 make use of it. The value will be stored only if you return
 298 <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 <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
 299 <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 object to be buffered and not sent
 300 immediately (if this is the default behavior based on your connection setup
 301 this will happen automatically).</p>
 302 <p>The prototype for this is:</p>
 303 <dl class="type">
 304 <dt id="_CPPv4N20memcached_callback_t30MEMCACHED_CALLBACK_GET_FAILURE21memcached_trigger_keyE">
 305 <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="sig-name 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>
 306 <dd></dd></dl>
 307
 308 </dd></dl>
 309
 310 <dl class="enumerator">
 311 <dt id="_CPPv4N20memcached_callback_t33MEMCACHED_CALLBACK_DELETE_TRIGGERE">
 312 <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="sig-name descname">MEMCACHED_CALLBACK_DELETE_TRIGGER</code><a class="headerlink" href="#_CPPv4N20memcached_callback_t33MEMCACHED_CALLBACK_DELETE_TRIGGERE" title="Permalink to this definition">¶</a><br /></dt>
 313 <dd><p>This function implements a trigger upon successful deletion of a key. The memcached_st structure will need to be cloned in order to make use of it.</p>
 314 <p>The prototype for this is:</p>
 315 <dl class="type">
 316 <dt id="_CPPv4N20memcached_callback_t33MEMCACHED_CALLBACK_DELETE_TRIGGER28memcached_trigger_delete_keyE">
 317 <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="sig-name 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>
 318 <dd></dd></dl>
 319
 320 </dd></dl>
 321
 322 </dd></dl>
 323
 324 </div>
 325 <div class="section" id="description">
 326 <h2>DESCRIPTION<a class="headerlink" href="#description" title="Permalink to this headline">¶</a></h2>
 327 <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
 328 provide function calls at points in the code, or return pointers to
 329 structures for particular usages.</p>
 330 <p><a class="reference internal" href="#_CPPv422memcached_callback_getP12memcached_st20memcached_callback_tP18memcached_return_t" title="memcached_callback_get"><code class="xref cpp cpp-func docutils literal notranslate"><span class="pre">memcached_callback_get()</span></code></a> takes a callback flag and returns the
 331 structure or function set by <a class="reference internal" href="#_CPPv422memcached_callback_setP12memcached_st20memcached_callback_tPKv" title="memcached_callback_set"><code class="xref cpp cpp-func docutils literal notranslate"><span class="pre">memcached_callback_set()</span></code></a>.</p>
 332 <p><a class="reference internal" href="#_CPPv422memcached_callback_setP12memcached_st20memcached_callback_tPKv" title="memcached_callback_set"><code class="xref cpp cpp-func docutils literal notranslate"><span class="pre">memcached_callback_set()</span></code></a> changes the function/structure assigned by a
 333 callback flag. No connections are reset.</p>
 334 <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
 335 if required for any of the callbacks.</p>
 336 </div>
 337 <div class="section" id="return-value">
 338 <h2>RETURN VALUE<a class="headerlink" href="#return-value" title="Permalink to this headline">¶</a></h2>
 339 <p><a class="reference internal" href="#_CPPv422memcached_callback_getP12memcached_st20memcached_callback_tP18memcached_return_t" title="memcached_callback_get"><code class="xref cpp cpp-func docutils literal notranslate"><span class="pre">memcached_callback_get()</span></code></a> return the function or structure that was
 340 provided. Upon error, nothing is set, null is returned, and the
 341 <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> 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>
 342 <p><a class="reference internal" href="#_CPPv422memcached_callback_setP12memcached_st20memcached_callback_tPKv" title="memcached_callback_set"><code class="xref cpp cpp-func 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
 343 successful setting, 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>
 344 </div>
 345 <div class="section" id="see-also">
 346 <h2>SEE ALSO<a class="headerlink" href="#see-also" title="Permalink to this headline">¶</a></h2>
 347 </div>
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