public static function stringFromColumnIndex($pColumnIndex = 0)  {          //  Using a lookup cache adds a slight memory overhead, but boosts speed          //  caching using a static within the method is faster than a class static,          //      though it's additional memory overhead          static $_indexCache = array();             if (!isset($_indexCache[$pColumnIndex])) {              // Determine column string              if ($pColumnIndex < 26) {                  $_indexCache[$pColumnIndex] = chr(65 + $pColumnIndex);              } elseif ($pColumnIndex < 702) {                  $_indexCache[$pColumnIndex] = chr(64 + ($pColumnIndex / 26)) . chr(65 + $pColumnIndex % 26);              } else {                 $_indexCache[$pColumnIndex] = chr(64 + (($pColumnIndex - 26) / 676)) . chr(65 + ((($pColumnIndex - 26) % 676) / 26)) . chr(65 + $pColumnIndex % 26);              }          }          return $_indexCache[$pColumnIndex];  }

PHPExcel_Cell::stringFromColumnIndex($i); // 从o开始

PHPExcel_Cell::columnIndexFromString('AA');