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POc function-like macro with argument list but without replacement list?
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copied!<p>A co-worker asked me to explain a bit of C code in <a href="http://memcached.org/" rel="nofollow">memcached</a>. I am at the point where I admit I do not understand it either.</p> <p>It has to do with C function-like macro definitions with parameters that do not also have a replacement list. For example, starting at line 2751 in memcached.c:</p> <pre><code> if (return_cas) { MEMCACHED_COMMAND_GET(c->sfd, ITEM_key(it), it->nkey, it->nbytes, ITEM_get_cas(it)); /* Goofy mid-flight realloc. */ if (i >= c->suffixsize) { char **new_suffix_list = realloc(c->suffixlist, sizeof(char *) * c->suffixsize * 2); if (new_suffix_list) { c->suffixsize *= 2; c->suffixlist = new_suffix_list; </code></pre> <p>MEMCACHED_COMMAND_GET() is defined on line 23 in trace.h:</p> <pre><code>#define MEMCACHED_COMMAND_GET(arg0, arg1, arg2, arg3, arg4) </code></pre> <p>C macro function-like definition with arguments, ok. No replacement list.</p> <p>The output of cpp on memcached.c shows the function-like macro turns into ';':</p> <pre><code># 2751 "memcached.c" if (return_cas) { ; if (i >= c->suffixsize) { char **new_suffix_list = realloc(c->suffixlist, sizeof(char *) * c->suffixsize * 2); if (new_suffix_list) { c->suffixsize *= 2; c->suffixlist = new_suffix_list; </code></pre> <p>Does anyone have any insight into why a programmer would include function-like macros without a replacement list like MEMCACHED_COMMAND_GET() that have no effect on the code produced? What purpose is being served by doing doing this? Thank you kindly in advance.</p>

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