CDatabase::Open

Статья
10/16/2008

Call this member function to initialize a newly constructed CDatabase object.

virtual BOOL Open(
   LPCTSTR lpszDSN,
   BOOL bExclusive = FALSE,
   BOOL bReadOnly = FALSE,
   LPCTSTR lpszConnect = _T("ODBC;"),
   BOOL bUseCursorLib = TRUE 
);

Параметры

lpszDSN
Specifies a data source name — a name registered with ODBC through the ODBC Administrator program. If a DSN value is specified in lpszConnect (in the form "DSN=<data-source>"), it must not be specified again in lpszDSN. In this case, lpszDSN should be NULL. Otherwise, you can pass NULL if you want to present the user with a Data Source dialog box in which the user can select a data source. For further information, see Remarks.
bExclusive
Not supported in this version of the class library. Currently, an assertion fails if this parameter is TRUE. The data source is always opened as shared (not exclusive).
bReadOnly
TRUE if you intend the connection to be read-only and to prohibit updates to the data source. All dependent recordsets inherit this attribute. The default value is FALSE.
lpszConnect
Specifies a connection string. The connection string concatenates information, possibly including a data source name, a user ID valid on the data source, a user authentication string (password, if the data source requires one), and other information. The whole connection string must be prefixed by the string "ODBC;" (uppercase or lowercase). The "ODBC;" string is used to indicate that the connection is to an ODBC data source; this is for upward compatibility when future versions of the class library might support non-ODBC data sources.
bUseCursorLib
TRUE if you want the ODBC Cursor Library DLL to be loaded. The cursor library masks some functionality of the underlying ODBC driver, effectively preventing the use of dynasets (if the driver supports them). The only cursors supported if the cursor library is loaded are static snapshots and forward-only cursors. The default value is TRUE. If you plan to create a recordset object directly from CRecordset without deriving from it, you should not load the cursor library.

Возвращаемое значение

Nonzero if the connection is successfully made; otherwise 0 if the user chooses Cancel when presented a dialog box asking for more connection information. In all other cases, the framework throws an exception.

Заметки

Your database object must be initialized before you can use it to construct a recordset object.

Примечание.
Calling the OpenEx member function is the preferred way to connect to a data source and initialize your database object.

If the parameters in your Open call do not contain enough information to make the connection, the ODBC driver opens a dialog box to obtain the necessary information from the user. When you call Open, your connection string, lpszConnect, is stored privately in the CDatabase object and is available by calling the GetConnect member function.

If you wish, you can open your own dialog box before you call Open to get information from the user, such as a password, then add that information to the connection string you pass to Open. Or you might want to save the connection string you pass so you can reuse it the next time your application calls Open on a CDatabase object.

You can also use the connection string for multiple levels of login authorization (each for a different CDatabase object) or to convey other data source-specific information. For more information about connection strings, see Chapter 5 in the Windows SDK.

It is possible for a connection attempt to time out if, for example, the DBMS host is unavailable. If the connection attempt fails, Open throws a CDBException.

Пример

// m_dbCust is a CDatabase object embedded in a CDocument class

if (bDefault)
{
   // Connect the object to a data source (no password)
   // the ODBC connection dialog box will always remain hidden
   m_dbCust.Open(_T("MFC_ODBCTest"), FALSE, FALSE, _T("ODBC;UID=JOES"));
}
else
{
   // ...Or, query the user for all connection information
   m_dbCust.Open(NULL);
}