Establishing a connection

Your application must establish a connection before it can carry out any database operations.

1. Allocate an ODBC environment:

   SQLHENV env; 
   SQLRETURN retcode; 
   retcode = SQLAllocHandle( SQL_HANDLE_ENV,  
                 SQL_NULL_HANDLE, &env );
   

2. Declare the ODBC version.

   By declaring that the application follows ODBC version 3, SQLSTATE values and some other version-dependent features are set to the proper behavior. For example:

   retcode = SQLSetEnvAttr( env,   
                 SQL_ATTR_ODBC_VERSION,               (void*)SQL_OV_ODBC3, 0);
   

3. If necessary, assemble the data source or connection string.

   Depending on your application, you can have a hard-coded data source or connection string, or you can store it externally for greater flexibility.

4. Allocate an ODBC connection handle:

   retcode = SQLAllocHandle( SQL_HANDLE_DBC, env, 
                 &dbc );
   

5. Set any connection attributes that must be set before connecting. (Some connection attributes must be set before establishing a connection, while others can be set either before or after.) For example:

   retcode = SQLSetConnectAttr( dbc,
   SQL_AUTOCOMMIT,     
                (SQLPOINTER)
   SQL_AUTOCOMMIT_OFF,
                 SQL_IS_UINTEGER );
   

6. Call the ODBC connection function:

   if (retcode == SQL_SUCCESS ||
      retcode == SQL_SUCCESS_WITH_INFO)
   {
      printf( "dbc allocated\n" );
      retcode = SQLConnect( dbc,
              (SQLCHAR*) "MANGO", SQL_NTS,
              (SQLCHAR* ) "sa", SQL_NTS,
              (SQLCHAR*) "", SQL_NTS );
      if (retcode == SQL_SUCCESS ||
        retcode == SQL_SUCCESS_WITH_INFO)
      {
        // successfully connected.
      }
   }
   

You can find a complete sample of establishing a connection in your installation directory.

• Every string passed to ODBC has a corresponding length. If the length is unknown, you can pass SQL_NTS indicating that it is a Null Terminated String whose end is marked by the null character (\0).

• You use the SQLSetConnectAttr function to control details of the connection. For example, the following statement turns off ODBC autocommit behavior:

retcode = SQLSetConnectAttr( dbc, SQL_AUTOCOMMIT,
            (SQLPOINTER)SQL_AUTOCOMMIT_OFF,
              SQL_IS_UINTEGER );