C language SDK programming-database programming-Use of ODBC Data Source APIs

I. programming interfaces for databases in Windows:
ODBC API

Dao

Oledb

ADO

Ado. net


ODBC is a function interface.
Dao, oledb, and ADO are COM components.
Ado.net is a programming interface on the. NET platform.
MFC provides ODBC and DAO Database Class cdatabase and cdaodatabase
ATL provides a template class for oledb

 

 

Ii. Use of ODBC APIs in SDK Programming

The following is an example:

# Include <windows. h>

# Include <SQL. h>
# Include <sqlext. h>
Void main ()

{

Henv; // environment handle

Hdbc; // data source handle

Hstmt; // execution statement handle

Unsigned char datasource [] = "Data Source Name"; // The Source Name set in the ODBC source

Unsigned char user [] = "User Name ";
// Account name of the database

Unsigned char PWD [] = "password"; // Database Password


Unsigned char search [] = "select XM from Stu where XH = 0 ";
Sqlreturn retcode; // record the return status of each SQL function

// Allocate the environment handle


Retcode =
Sqlallocenv (& henv); // among others
Sqlallochandle (SQL _handle_env, SQL _null_handle, & henv );

// Set ODBC Environment version 3.0


Retcode =
Sqlsetenvattr (henv, SQL _attr_odbc_version, (void *) SQL _ov_odbc3, 0 );

// Allocate a connection handle


Retcode =
Sqlallocconnect (henv, & hdbc );
// Wait

Sqlallochandle (SQL _handle_dbc, henv, & hdbc );

// Set the connection attribute. The logon timeout value is * rgbvalue second (not available)
// Sqlsetconnectattr (hdbc, SQL _login_timeout, (sqlpointer) (rgbvalue), 0 );

 

// Directly connect to the data source

// For Windows authentication, the second and third parameters can be null or any string

// SQL _cnt is "null-terminated string"


Retcode =
Sqlconnect (hdbc, datasource, SQL _cnt, user,
SQL _nt
, PWD,
SQL _nt
);

// Allocate statement handle


Retcode =
Sqlallocstmt (hdbc, & hstmt );
// Wait for sqlallochandle (SQL _handle_stmt, hdbc, & hstmt );

// Directly execute the query statement
Retcode = sqlexecdirect (hstmt, search, SQL _cnt );

// Bind the data buffer to the corresponding fields in the database (I is the query result set column number, querydata is the binding buffer, buff_length is the buffer length)

Sqlbindcol (hstmt, I, SQL _c_char, querydata [I-1], buff_length, 0 );

// Traverse the result set to the corresponding buffer

Sqlfetch (hstmt );

/*

* Operations related to traversal results, such as display

*

*/

// Pay attention to the release order. Otherwise, an unknown error will occur!

Sqlfreehandle (SQL _handle_stmt, hstmt );
Sqldisconnect (hdbc );
Sqlfreehandle (SQL _handle_dbc, hdbc );
Sqlfreehandle (SQL _handle_env, henv );
}

 

 

Iii. Ado can be programmed directly using the SDK. You only need to import the ADO library.

 

# Import "C:/program files/common files/system/ADO/msado15.dll" no_namespace Rename ("EOF", "adoeof ")
// Import the ADO Library

# Include <windows. h>

# Include <stdio. h>

Void main ()
{
Try
{
Lpctstr databasefile = "C: // program files // Microsoft SQL Server // mssql.2 // MSSQL // data // student. MDF ";
Win32_find_data WFD;
Handle hfile = findfirstfile (databasefile, & WFD );
If (hfile = invalid_handle_value)
{
Printf ("cannot find the database file/N ");
System ("pause ");
Return;
}

Coinitialize (null );
Hresult hr;
_ Connectionptr

Myconnection;

Myconnection. createinstance (_ uuidof (connection ));
HR = myconnection-> open (_ bstr_t ("provider = Microsoft. jet. oledb.4.0; Data Source = C: // program files // Microsoft SQL Server // mssql.2 // MSSQL // data // student. MDF "),
_ Bstr_t (""),
_ Bstr_t (""),
Admodeunknown );
If (myconnection = NULL)
{
Printf ("cocould not acquire a connection interface ");
System ("pause ");
Return;
}

_ Commandptr

Pcommand;
Pcommand. createinstance (_ uuidof (command ));
Pcommand-> activeconnection = myconnection;
Pcommand-> commandtext = "select * from Stu ";

_ Recordsetptr

Precordset;
Precordset. createinstance (_ uuidof (recordset ));
Precordset-> cursorlocation = aduseclient;
Precordset-> open (idispatch *) pcommand,
Vtmissing,
Adopenstatic,
Adlockbatchoptimistic,
Adcmdunknown );

_ Variant_t column;
While (! Precordset-> adoeof)
{
Column = precordset-> getcollect ("Administrator ");
If (column. VT! = Vt_null)
Printf (char *) _ bstr_t (column ));
Printf ("/t ");
Column = precordset-> getcollect ("password ");
If (column. VT! = Vt_null)
Printf (char *) _ bstr_t (column ));
Printf ("/N ");
Precordset-> movenext ();

}

Printf ("Hello world! /N ");
Myconnection-> close ();
System ("pause ");
Couninitialize ();
}
Catch (_ com_error & E)
{
_ Bstr_t bstrerror (E. errormessage ());
Lptstr strerror = (char *) bstrerror;
Printf (strerror );
Printf ("/N ");

System ("pause ");
}

}