Connecting to a Data Source (ODBC)
After allocating environment and connection handles and setting any connection attributes, the application connects to the data source or driver. There are three functions you can use to connect:
For more information about making connections to a data source, including the various connection string options available, see Using Connection String Keywords with SQL Server Native Client.
SQLConnect is the simplest connection function. It accepts three parameters: a data source name, a user ID, and a password. Use SQLConnect when these three parameters contain all the information needed to connect to the database. To do this, build a list of data sources using SQLDataSources; prompt the user for a data source, user ID, and password; and then call SQLConnect.
SQLConnect assumes that a data source name, user ID, and password are sufficient to connect to a data source and that the ODBC data source contains all other information the ODBC driver needs to make the connection. Unlike SQLDriverConnect and SQLBrowseConnect, SQLConnect does not use a connection string.
SQLDriverConnect is used when more information than the data source name, user ID, and password is required. One of the parameters to SQLDriverConnect is a connection string containing driver-specific information. You might use SQLDriverConnect instead of SQLConnect for the following reasons:
To specify driver-specific information at connect time.
To request that the driver prompt the user for connection information.
To connect without using an ODBC data source.
The SQLDriverConnect connection string contains a series of keyword-value pairs that specify all connection information supported by an ODBC driver. Each driver supports the standard ODBC keywords (DSN, FILEDSN, DRIVER, UID, PWD, and SAVEFILE) in addition to driver-specific keywords for all connection information supported by the driver. SQLDriverConnect can be used to connect without a data source. For example, an application that is designed to make a "DSN-less" connection to an instance of SQL Server can call SQLDriverConnect with a connection string that defines the login ID, password, network library, server name to connect to, and default database to use.
When using SQLDriverConnect, there are two options for prompting the user for any needed connection information:
Application dialog box
You can create an application dialog box that prompts for connection information, and then calls SQLDriverConnect with a NULL window handle and DriverCompletion set to SQL_DRIVER_NOPROMPT. These parameter settings prevent the ODBC driver from opening its own dialog box. This method is used when it is important to control the user interface of the application.
Driver dialog box
You can code the application to pass a valid window handle to SQLDriverConnect and set the DriverCompletion parameter to SQL_DRIVER_COMPLETE, SQL_DRIVER_PROMPT, or SQL_DRIVER_COMPLETE_REQUIRED. The driver then generates a dialog box to prompt the user for connection information. This method simplifies the application code.
SQLBrowseConnect, like SQLDriverConnect, uses a connection string. However, by using SQLBrowseConnect, an application can construct a complete connection string iteratively with the data source at run time. This allows the application to do two things:
Build its own dialog boxes to prompt for this information, thereby retaining control over its user interface.
Browse the system for data sources that can be used by a particular driver, possibly in several steps.
For example, the user might first browse the network for servers and, after choosing a server, browse the server for databases accessible by the driver.
When SQLBrowseConnect completes a successful connection, it returns a connection string that can be used on subsequent calls to SQLDriverConnect.
The SQL Server Native Client ODBC driver always returns SQL_SUCCESS_WITH_INFO on a successful SQLConnect, SQLDriverConnect, or SQLBrowseConnect. When an ODBC application calls SQLGetDiagRec after getting SQL_SUCCESS_WITH_INFO, it can receive the following messages:
Indicates that SQL Server put the user's context into the default database defined in the data source, or into the default database defined for the login ID used in the connection if the data source did not have a default database.
Indicates the language being used on the server.
The following example shows the message returned on a successful connection by the system administrator:
szSqlState = "01000", *pfNativeError = 5701, szErrorMsg="[Microsoft][SQL Server Native Client][SQL Server] Changed database context to 'pubs'." szSqlState = "01000", *pfNativeError = 5703, szErrorMsg="[Microsoft][SQL Server Native Client][SQL Server] Changed language setting to 'us_english'."
You can ignore messages 5701 and 5703; they are only informational. You should not, however, ignore a SQL_SUCCESS_WITH_INFO return code because messages other than 5701 or 5703 may be returned. For example, if a driver connects to a server running an instance of SQL Server with outdated catalog stored procedures, one of the errors returned through SQLGetDiagRec after a SQL_SUCCESS_WITH_INFO is:
SqlState: 01000 pfNative: 0 szErrorMsg: "[Microsoft][SQL Server Native Client]The ODBC catalog stored procedures installed on server my65server are version 06.50.0193; version 07.00.0205 or later is required to ensure proper operation. Please contact your system administrator."
The error handling function of an application for SQL Server connections should call SQLGetDiagRec until it returns SQL_NO_DATA. It should then act on any messages other than the ones with a pfNative code of 5701 or 5703.
Verifying Connection State
The behavior of SQL_ATTR_CONNECTION_DEAD and SQL_COPT_SS_CONNECTION_DEAD in SQL Server 2000 and later is different from the behavior in earlier versions. In SQL Server 2000 and later, SQL_ATTR_CONNECTION_DEAD returns the most recent state of the connection, which may not be the current connection state. However, SQL_COPT_SS_CONNECTION_DEAD always queries the Net-Library for the current state of the connection.
To differentiate between these behaviors, SQL_COPT_SS_CONNECTION_DEAD is given a new value in the SQL Server 2000 and later include files. Applications using this attribute that are built using the SQL Server 2000 and later headers will return an error (HY092, Invalid attribute/option identifier) if the applications are run using a SQL Server version 7.0 driver. We recommend that the application check the version of driver being used before calling SQLGetConnectAttr, and then use SQL_ATTR_CONNECTION_DEAD in place of SQL_COPT_SS_CONNECTION_DEAD if the application is running on a SQL Server 7.0 driver.