Common methods for adjusting ADO in VC
Overview
For programmers that write database programs on Windows, ActiveX Data Objects (ADO) is the most commonly used technology, which can make database connections and data access via ADO. However, when using ADO in VC , since it is called using COM, some systems often have problems that cannot be compiled, or use the program illegal errors, and I want to introduce the common method of calling ADO in VC ..
1. Import the COM file Msado15.dll with Import into ADO
E.g:
#import "c: / program files / compon files / system / ado / msado15.dll" /
NO_NAMESPACE
2, the initialization of COM use
HRESULT COMINIT ()
{
HRESULT HR = S_OK; / / Default return value
IF failed (coinitialize) // COM initialization call
{
Couninitialize ();
HR = e_unexpected;
}
Return HR;
}
3, establish a database connection
HRESULT ConnectToDB (LPSTR PUSERID, // User Name
LPSTR PCONNSTRING, // Connecting strings
LPSTR PUSERPASSWORD, // User Password
ConnectOptionNum ConnectOption) // Connection parameters
{
HRESULT HR = S_OK; / / Default return value
_ConnectionPtr PtrConn; / / Define Connection Objects
Try
{
// Create a connection entity
HR = ptrconn.createInstance (__ uuidof (connection));
/ / Set the maximum number of seconds waiting to wait, default is 15 seconds
PtrConn-> ConnectionTimeout = 20
// Open connection
HR = Ptrconn-> Open (PConnString,
PUSERID,
PUSERPASSWORD,
ConnectOption;
Return HR;
}
Catch (_COM_ERROR & PCOMERROR)
{
... // Error handling
Return E_UNEXPECTED;
}
}
4. Execute a SQL query to get a data set (Recordset)
_RecordSetPtr getRecordset (LPSTR strsql, _connectionptr ptronn)
{
Try
{
RecordSetPtr Ptrrs; // Recordset object
// Create a RecordSet object entity
PTRRS.CREATEINSTANCE (__ uuidof (recordset);
Ptrrs-> Open (strsql,
PtrConn.GetInterfacePtr (),
AdopenForwardonly,
AdlockunSpecified,
AdcmdText);
or
PTRRS = PTRCONN -> EXECUTE (M_ strsql, null, adcmdtext);
Return PTRRS;
}
Catch (_COM_ERROR & A_PCOMERROR)
{
....// Error handling
Return NULL;
}
}
5. Get column name HRESULT GETCOLUMNNAMES by the data set
_RecordSetPtr Ptrrs, // Recordset object
CHAR STRCOLNAMES [] [255],
DatatyPeenum iColtypes [])
{
Try
{// parameter variable
_VARIANT_T L_VAINDEX;
l_vaindex.vt = vt_i2;
// columns total
Long LCOLCOUNT;
LCOLCOUNT = PTRRS -> Fields-> Count;
// Cycle the properties and names of the column
For (int IINDEX = 0; IIndex { l_vaindex.ival = iINDex; // Setting the loop index / / Get a field name Sprintf (StrColnames [IIndex], "% S", (Lpstr) PTRRS -> Fields-> GetItem (l_vaindex) -> name); // get field properties Icoltypes = Ptrrs -> Fields-> GetItem (l_vaindex) -> Type; } } Return S_OK; } Catch (_COM_ERROR & A_PCOMERROR) { .... // Error handling Return E_UNEXPECTED; } Catch (...) { .... // Error handling Return E_UNEXPECTED; } } 6. Get the current line record through the data set (RECORDSET) HRESULT GETONERECORD _RecordSetPtr PTRRS, Const long lnofcolumns, _variant_t varvalue []) { Try { // Parameter variable _VARIANT_T L_VAINDEX; l_vaindex.vt = vt_i2; // loop to get the value of the column For (long lindex = 0; lindex { l_vaindex.ival = lindex; // Take a field value VARVALUE [LINDEX] = Ptrrs-> Fields-> GetItem (l_vaindex) -> value; } Return S_OK; } Catch (_COM_ERROR & A_PCOMERROR) { .... // Error handling Return E_UNEXPECTED; } Catch (...) { .... // Error handling Return E_UNEXPECTED; } } 7. Error information Void Errorfunc (_COM_ERROR & PCOMERROR, _CONNECTIONPTR PTRCONN); { // COM error // When performing a COM function, if an error, you can capture the abnormality of _COM_ERROR. Char lpcomerrorstr512]; Sprintf (lpcomerroSTR512, "ErrorCode =% 08LX / Error Message =% S / Source =% s / Description =% s ", Pcomerror.Error (), // error number pcomerror.ErrorMessage (), // error message (Lpcstr) pcomerror.source (), // Error source (LPCSTR) pcomerror.description ()); // Error Description // We can see the above code, and you can get all the error of COM in the _COM_ERROR object. // ADO error Errorptr Perr = NULL; IF ((ptrconn -> errors-> count)> 0) { Long ncount = ptrconn -> errors-> count; For (long i = 0; i { Perr = a_pconnptr-> errors-> GetItem (i); Char l_pcherrorstring [512]; Sprintf (l_pcherrorstring, "error: / n error number:% x / t% s", Perr-> number, // error number Perr-> description); // Error Description } } // ADO handle, there is a record in the Connection object, you can access // Connection object acquires error numbers and error messages.
