The flags correspond to those for the open() system
call. (Typically 0 means read-only, 1 means write-only, and 2
means read and write.)
Returns a dbase_identifier for the opened database, or
FALSE if the database
couldn't be opened.
注: 當安全模式開啟,PHP會檢查執行的腳本和 要操作的檔案或目錄是否有相同的UID(擁有者)。