如何处理未使用的变量

有一些函数传入了没有任何作用的变量，但是，这些变量在以后可能会用上（可扩展性）。

而编译器一般会发出警告，提示该变量没有被使用。如何处理这种case呢？

业界有一行统一的代码来解决这个问题。

handler_t stat_cache_handle_fdevent(server *srv, void *_fce, int revent) {
size_t i;
stat_cache *sc = srv->stat_cache;
size_t events;

UNUSED(_fce);
/* */

if ((revent & FDEVENT_IN) &&
sc->fam) {

events = FAMPending(sc->fam);

for (i = 0; i < events; i++) {
FAMEvent fe;
fam_dir_entry *fam_dir;
splay_tree *node;
int ndx, j;

FAMNextEvent(sc->fam, &fe);

/* handle event */

switch(fe.code) {
case FAMChanged:
case FAMDeleted:
case FAMMoved:
/* if the filename is a directory remove the entry */

fam_dir = fe.userdata;
fam_dir->version++;

/* file/dir is still here */
if (fe.code == FAMChanged) break;

/* we have 2 versions, follow and no-follow-symlink */

for (j = 0; j < 2; j++) {
buffer_copy_string(sc->hash_key, fe.filename);
buffer_append_long(sc->hash_key, j);

ndx = hashme(sc->hash_key);

sc->dirs = splaytree_splay(sc->dirs, ndx);
node = sc->dirs;

if (node && (node->key == ndx)) {
int osize = splaytree_size(sc->dirs);

fam_dir_entry_free(node->data);
sc->dirs = splaytree_delete(sc->dirs, ndx);

assert(osize - 1 == splaytree_size(sc->dirs));
}
}
break;
default:
break;
}
}
}

if (revent & FDEVENT_HUP) {
/* fam closed the connection */
srv->stat_cache->fam_fcce_ndx = -1;

fdevent_event_del(srv->ev, &(sc->fam_fcce_ndx), FAMCONNECTION_GETFD(sc->fam));
fdevent_unregister(srv->ev, FAMCONNECTION_GETFD(sc->fam));

FAMClose(sc->fam);
free(sc->fam);

sc->fam = NULL;
}

return HANDLER_GO_ON;
}

其中的：

UNUSED(_fce);

就是用来处理这种情况。

UNUSED宏定义如下：

#define UNUSED(x) ( (void)(x) )

明白了吧？