uschar filebuffer[256];
(void)sprintf(CS filebuffer, "%.256s.db", filename);
 rc = lf_check_file(-1, filebuffer, S_IFREG, modemask, owners, owngroups,
  "dbm", errmsg);
if (rc < 0)        /* stat() failed */
  {
  (void)sprintf(CS filebuffer, "%.256s.dir", filename);
  rc = lf_check_file(-1, filebuffer, S_IFREG, modemask, owners, owngroups,
    "dbm", errmsg);
   if (rc == 0)     /* x.dir was OK */
     {
     (void)sprintf(CS filebuffer, "%.256s.pag", filename);
     rc = lf_check_file(-1, filebuffer, S_IFREG, modemask, owners, owngroups,
       "dbm", errmsg);
     }
   }
 }

define STR "string"
size_t len=strlen("part"STR"part 2");

"%."PATH_MAX".db"