Detailed description of configuring the data source and connecting to ACCESS through VC ++ ADO

# Includeiostream. h # importc: programfilescommonfilessystemadomsado15.dllno _ namespacerename (EOF, adoEOF) the dll required for connecting to the database from ADO. during compilation, the system will generate msado15.tlh for us, ado15.tli two C header files to define the ADO library. Note that the import here must be placed

# I nclude iostream. h # import c:/program files/common files/system/ado/msado15.dll no_namespace rename (EOF, adoEOF) // dll required for connecting to the database by ADO, during compilation, the system will generate msado15.tlh for us and the ado15.tli two C header files to define the ADO library // note that the import here must be placed

# I nclude
# Import "c:/program files/common files/system/ado/msado15.dll" no_namespace rename ("EOF", "adoEOF ")
// The dll required by ADO to connect to the database. during compilation, the system will generate msado15.tlh and ado15.tli two C ++ header files for us to define the ADO library.
// Note that the import here must be placed in a row

Int main (){

// This program uses ADO to connect to ACCESS (which is included when the office is installed). The database suffix is. mdb running platform vc6.0.
// 2003 the Platform says
//---------------------------------------------------------------------------------

// The ADO database is connected in five steps,
// First, obtain the connection (only to where the database is located)
// Second, open the connection (required username and password)
// Third, obtain the character set ResultSet (similar to the data storage object of arrays ),
// Fourth, display data
// Fifth, close the dataset and close the connection

// Create a connection object
_ ConnectionPtr m_pConnection;

// Initialize the connection
CoInitialize (NULL );

//---------------------------------------------------------------------------------
// Step 1. Obtain the connection
//---------------------------------------------------------------------------------
// Create and obtain a database Connection instance with the same Connection,
// You can also think of him as a handle (for movie tickets), so that he is eligible to use the resources in the database.
M_pConnection.CreateInstance (_ uuidof (Connection ));

// Errors may occur during database connection, such as data source setting or incorrect user name and password.
// Use try {...} catch () {...} to catch exceptions (errors) in try)
// And put these exceptions in the Variable _ com_error e. We can get the error information with him.
// In addition, when an error occurs, the program must run catch () {...}. We can see that if a connection error occurs
// Cout <"database connection failed. Check whether mydb. mdb is in the current path! "< // Return FALSE; a program will be launched later. If you do not add a try, the system will crash when a program error occurs.
// Therefore, try can also be seen as an error handling (Exception Handling)
Try
{//---------------------------------------------------------------------------------
// Step 2. Open the connection parameters and separate them.
//---------------------------------------------------------------------------------

// Provider = Microsoft. Jet. OLEDB.4.0; access vendor
// Data Source = mydb. mdb "," "," ", adModeUnknown Database Name, username (blank), password (blank), default connection mode
// For this parameter: ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ~~~~~~~~~~~~~~~ (1)
/* AdModeUnknown: default. The current permission is not set
AdModeRead: Read-Only
AdModeWrite: Write only
AdModeReadWrite: read/write
AdModeShareDenyRead: blocks other Connection objects and opens the Connection with the read permission.
AdModeShareDenyWrite: blocks other Connection objects and opens the Connection with write permission.
Admodemo-exclusive: prevents other Connection objects from opening connections.
AdModeShareDenyNone: allows other programs or objects to establish connections with any permissions.
*/
// Through this statement, our database connection is actually implemented. m_pConnection has content (value attached)
M_pConnection-> Open ("Provider = Microsoft. Jet. OLEDB.4.0; Data Source = mydb. mdb", "", "", adModeUnknown );

}
Catch (_ com_error e) // catch exceptions
{
Cout <"database connection failed. Check whether mydb. mdb is in the current path! "< Return FALSE;
}

// DataSet object
_ RecordsetPtr m_pRecordset;
// Instantiate a dataset
M_pRecordset.CreateInstance (_ uuidof (Recordset ));

//---------------------------------------------------------------------------------
// Step 3: Obtain the dataset
//---------------------------------------------------------------------------------
// Although the connection is established, whether there is a data table (test table) in the connected database is unknown.
// Therefore, it is also necessary to capture Possible Errors
Try
{
M_pRecordset-> Open ("SELECT * FROM test", // It is a data query string (the so-called SQL statement)
// These statements are usually divided into data query (select) and insert (insert) statements)
// Update and delete)
// Whether the command can be executed is determined by the preceding (1 ).

M_pConnection.GetInterfacePtr (), // gets the IDispatch pointer of the database connected to the database

AdOpenDynamic, // dynamic cursor. All database operations will be immediately reflected in each user record set

AdLockOptimistic, // Optimistic Locking mode. The record is locked only when you call the Update method. Here
// You can still update, insert, or delete data.

AdCmdText); // The queried data is displayed on the console.
}
Catch (_ com_error * e)
{
Cout < ErrorMessage () < }

_ Variant_t var;
Char * ID, * name;

Try // obtain the table, but the table does not necessarily have data
{
If (! M_pRecordset-> BOF) // The data table contains data.
M_pRecordset-> MoveFirst (); // move the cursor (the dataset name in the database) to the first record.
Else {
Cout <"table data is empty" < Return 1;
}

// Configure //--------------------------------------------------------------------------------------------------------------------------
// Step 4: Display Data
// Configure //---------------------------------------------------------------------------------------------------------------------------

While (! M_pRecordset-> adoEOF) // corresponds to the previous rename ("EOF", "adoEOF ").
// AdoEOF replaces EOF (of course, you can also use EOF if there is no rename above)
// Determine whether the cursor has reached the last data entry
{
Var = m_pRecordset-> GetCollect ("ID"); // This is a method for obtaining fields in a table. "ID" indicates the table field name.
If (var. vt! = VT_NULL) // determines whether the record has no data.
ID = _ com_util: ConvertBSTRToString (_ bstr_t) var); // conversion is required because the data obtained may not contain characters.
// Convert them into strings so that they can be displayed on the screen

Var = m_pRecordset-> GetCollect ("name ");
If (var. vt! = VT_NULL)
Name = _ com_util: ConvertBSTRToString (_ bstr_t) var );

Cout <
M_pRecordset-> MoveNext (); // The cursor moves toward the next record
}
}
Catch (_ com_error * e) // catch exceptions
{
Cout < ErrorMessage () < }
// Configure //--------------------------------------------------------------------------------------
// Close the dataset
// Configure //-----------------------------------------------------------------------------------
M_pRecordset-> Close ();
M_pRecordset = NULL;

// Configure //--------------------------------------------------------------------------------------
// Close the database connection
// Configure //--------------------------------------------------------------------------------------
If (m_pConnection-> State)
M_pConnection-> Close ();
M_pConnection = NULL;

// These two steps must be done. Otherwise, the memory may be exhausted for a long time.
Return 0;
}