Fetch Rows from a Result Set (OLE DB)

Article
04/01/2012

This sample shows how to fetch rows from a result set. This sample is not supported on IA64.

This sample requires the AdventureWorks sample database, which you can download from the Microsoft SQL Server Samples and Community Projects home page.

Security Note
When possible, use Windows Authentication. If Windows Authentication is not available, prompt users to enter their credentials at run time. Avoid storing credentials in a file. If you must persist credentials, you should encrypt them with the Win32 crypto API.

Example

Description

Compile with ole32.lib oleaut32.lib and execute the following C++ code listing. This application connects to your computer's default SQL Server instance. On some Windows operating systems, you will need to change (localhost) or (local) to the name of your SQL Server instance. To connect to a named instance, change the connection string from L"(local)" to L"(local)\\name" , where name is the named instance. By default, SQL Server Express installs to a named instance. Make sure your INCLUDE environment variable includes the directory that contains sqlncli.h.

Code

// compile with: ole32.lib oleaut32.lib
int InitializeAndEstablishConnection();
int ProcessResultSet();

#define UNICODE
#define _UNICODE
#define DBINITCONSTANTS
#define INITGUID
#define OLEDBVER 0x0250   // to include correct interfaces

#include <stdio.h>
#include <tchar.h>
#include <stddef.h>
#include <windows.h>
#include <iostream>
#include <oledb.h>
#include <sqlncli.h>
#include <msdadc.h>   // for IDataConvert
#include <msdaguid.h>   // for IDataConvert

using namespace std;

IDBInitialize* pIDBInitialize = NULL;
IDBProperties* pIDBProperties = NULL;
IDBCreateSession* pIDBCreateSession = NULL;
IDBCreateCommand* pIDBCreateCommand = NULL;
ICommandText* pICommandText = NULL;
IRowset* pIRowset = NULL;
IColumnsInfo* pIColumnsInfo = NULL;

DBCOLUMNINFO* pDBColumnInfo = NULL;
IAccessor* pIAccessor =  NULL;
DBPROP InitProperties[4];
DBPROPSET rgInitPropSet[1];

ULONG i, j;
HRESULT hr;
DBROWCOUNT cNumRows = 0;
DBORDINAL lNumCols;
WCHAR* pStringsBuffer;
DBBINDING* pBindings;
DBLENGTH ConsumerBufColOffset = 0;
HACCESSOR hAccessor;
DBCOUNTITEM lNumRowsRetrieved;
HROW hRows[10];
HROW* pRows = &hRows[0];

int main() {
   // The command to execute.
   WCHAR* wCmdString = OLESTR("SELECT StandardCost, ListPrice FROM Production.Product WHERE ListPrice > 14.00");

   // Call a function to initialize and establish connection. 
   if (InitializeAndEstablishConnection() == -1) {
      // Handle error.
      cout << "Failed to initialize and connect to the server.\n";
      return -1;
   }

   // Create a session object.
   if (FAILED(pIDBInitialize->QueryInterface( IID_IDBCreateSession,
      (void**) &pIDBCreateSession))) {
         cout << "Failed to obtain IDBCreateSession interface.\n";
         // Handle error.
         return -1;
   }

   if (FAILED(pIDBCreateSession->CreateSession( NULL, 
      IID_IDBCreateCommand, 
      (IUnknown**) &pIDBCreateCommand))) {
         cout << "pIDBCreateSession->CreateSession failed.\n";
         // Handle error.
         return -1;
   }

   // Access the ICommandText interface.
   if (FAILED(pIDBCreateCommand->CreateCommand( NULL, 
      IID_ICommandText, 
      (IUnknown**) &pICommandText))) {
         cout << "Failed to access ICommand interface.\n";
         // Handle error.
         return -1;
   }

   // Use SetCommandText() to specify the command text.
   if (FAILED(pICommandText->SetCommandText(DBGUID_DBSQL, wCmdString))) {
      cout << "Failed to set command text.\n";
      // Handle error.
      return -1;
   }

   // Execute the command.
   if (FAILED(hr = pICommandText->Execute( NULL, 
      IID_IRowset, 
      NULL, 
      &cNumRows, 
      (IUnknown **) &pIRowset))) {
         cout << "Failed to execute command.\n";
         // Handle error.
         return -1;
   }

   // Process the result set.
   ProcessResultSet(); 

   pIRowset->Release();

   // Free up memory.
   pICommandText->Release();
   pIDBCreateCommand->Release();
   pIDBCreateSession->Release();

   if (FAILED(pIDBInitialize->Uninitialize())) {
      // Uninitialize is not required, but it fails if an interface
      // has not been released.  This can be used for debugging.
      cout << "Problem uninitializing.\n";
   }

   pIDBInitialize->Release();
   CoUninitialize();
};

int InitializeAndEstablishConnection() {    
   CoInitialize(NULL);

   // Obtain access to the SQLNCLI provider.
   hr = CoCreateInstance( CLSID_SQLNCLI11,
      NULL,
      CLSCTX_INPROC_SERVER,
      IID_IDBInitialize,
      (void **) &pIDBInitialize);


   if (FAILED(hr)) {
      printf("Failed to get IDBInitialize interface.\n");
      // Handle errors here.
      return -1;
   }

   // Initialize the property values needed to establish the connection.
   for ( i = 0 ; i < 4 ; i++ )
      VariantInit(&InitProperties[i].vValue);

   // Server name.
   InitProperties[0].dwPropertyID = DBPROP_INIT_DATASOURCE;
   InitProperties[0].vValue.vt = VT_BSTR;

   InitProperties[0].vValue.bstrVal= SysAllocString(L"(local)");
   InitProperties[0].dwOptions = DBPROPOPTIONS_REQUIRED;
   InitProperties[0].colid = DB_NULLID;

   // Database.
   InitProperties[1].dwPropertyID = DBPROP_INIT_CATALOG;
   InitProperties[1].vValue.vt = VT_BSTR;
   InitProperties[1].vValue.bstrVal = SysAllocString(L"AdventureWorks");
   InitProperties[1].dwOptions = DBPROPOPTIONS_REQUIRED;
   InitProperties[1].colid = DB_NULLID;

   InitProperties[2].dwPropertyID = DBPROP_AUTH_INTEGRATED;
   InitProperties[2].vValue.vt = VT_BSTR;
   InitProperties[2].vValue.bstrVal = SysAllocString(L"SSPI");
   InitProperties[2].dwOptions = DBPROPOPTIONS_REQUIRED;
   InitProperties[2].colid = DB_NULLID;

   // Properties are set, now construct the DBPROPSET structure (rgInitPropSet) used to pass 
   // an array of DBPROP structures (InitProperties) to the SetProperties method.
   rgInitPropSet[0].guidPropertySet = DBPROPSET_DBINIT;
   rgInitPropSet[0].cProperties = 4;
   rgInitPropSet[0].rgProperties = InitProperties;

   // Set initialization properties.
   hr = pIDBInitialize->QueryInterface(IID_IDBProperties, (void **)&pIDBProperties);
   if (FAILED(hr)) {
      cout << "Failed to get IDBProperties interface.\n";
      // Handle errors here.
      return -1;
   }

   hr = pIDBProperties->SetProperties(1, rgInitPropSet); 
   if (FAILED(hr)) {
      cout << "Failed to set initialization properties.\n";
      // Handle errors here.
      return -1;
   }

   pIDBProperties->Release();

   // Now establish the connection to the data source.
   if (FAILED(pIDBInitialize->Initialize())) {
      cout << "Problem in establishing connection to the data"
         "source.\n";
      // Handle errors here.
      return -1;
   }
   return 0;
}

// Retrieve and display data resulting from a query.
int ProcessResultSet() {
   // Obtain access to the IColumnInfo interface, from the Rowset object.
   hr = pIRowset->QueryInterface(IID_IColumnsInfo, (void **)&pIColumnsInfo);
   if (FAILED(hr)) {
      cout << "Failed to get IColumnsInfo interface.\n";
      // Handle errors here.
      return -1;
   } 

   // Retrieve the column information.
   pIColumnsInfo->GetColumnInfo(&lNumCols, &pDBColumnInfo, &pStringsBuffer);

   // Free the column information interface.
   pIColumnsInfo->Release();

   // Create a DBBINDING array.
   DBBINDING * p = (pBindings = new DBBINDING[lNumCols]);
   if (!(p /* pBindings = new DBBINDING[lNumCols] */ ))
      return -1;

   // Using the ColumnInfo structure, fill out the pBindings array.
   for ( j = 0 ; j < lNumCols ; j++ ) {
      pBindings[j].iOrdinal = j+1;
      pBindings[j].obValue = ConsumerBufColOffset;
      pBindings[j].pTypeInfo = NULL;
      pBindings[j].pObject = NULL;
      pBindings[j].pBindExt = NULL;
      pBindings[j].dwPart = DBPART_VALUE;
      pBindings[j].dwMemOwner = DBMEMOWNER_CLIENTOWNED;
      pBindings[j].eParamIO = DBPARAMIO_NOTPARAM;
      pBindings[j].cbMaxLen = (pDBColumnInfo[j].wType == DBTYPE_WSTR) ? pDBColumnInfo[j].ulColumnSize * 2 : pDBColumnInfo[j].ulColumnSize;
      pBindings[j].dwFlags = 0;
      pBindings[j].wType = pDBColumnInfo[j].wType;
      pBindings[j].bPrecision = pDBColumnInfo[j].bPrecision;
      pBindings[j].bScale = pDBColumnInfo[j].bScale;

      // Compute the next buffer offset.
      ConsumerBufColOffset = 
         ConsumerBufColOffset + pBindings[j].cbMaxLen;
   };

   // Get the IAccessor interface.
   hr = pIRowset->QueryInterface(IID_IAccessor, (void **) &pIAccessor);
   if (FAILED(hr)) {
      cout << "Failed to obtain IAccessor interface.\n";
      // Handle errors here.
      return -1;
   }

   // Create an accessor from the set of bindings (pBindings).
   pIAccessor->CreateAccessor(DBACCESSOR_ROWDATA, lNumCols, pBindings, 0, &hAccessor, NULL);

   // Print column names.
   for ( j = 0 ; j < lNumCols ; j++ )
      printf("%-40S", pDBColumnInfo[j].pwszName);

   printf("\n");   // new line after the column names

   // Get a set of 10 rows.
   pIRowset->GetNextRows( NULL, 0, 10, &lNumRowsRetrieved, &pRows);

   // Allocate space for the row buffer.
   BYTE * pBuffer = new BYTE[ConsumerBufColOffset];
   if (!(pBuffer /* = new BYTE[ConsumerBufColOffset] */ )) {
      // Free up all allocated memory.
      pIAccessor->ReleaseAccessor(hAccessor, NULL);
      pIAccessor->Release();
      delete [] pBindings;

      return 0;
   }

   // Create an instance of the data conversion library to convert DBTYPE_CY to string for display
   IDataConvert* pIDataConvert;
   CoCreateInstance(CLSID_OLEDB_CONVERSIONLIBRARY,
      NULL,
      CLSCTX_INPROC_SERVER,
      IID_IDataConvert,
      (void**)&pIDataConvert);

   // variables used in DataConvert
   DBLENGTH cbDstLength;
   DBSTATUS dbsStatus;
   char strCurrency0[25];
   char strCurrency1[25];

   // Display the rows.
   while ( lNumRowsRetrieved > 0 ) {
      // For each row, print the column data.
      for ( j = 0 ; j < lNumRowsRetrieved ; j++ ) {
         // Clear the buffer.
         memset(pBuffer, 0, ConsumerBufColOffset);

         // Get the row data values.
         pIRowset->GetData(hRows[j], hAccessor, pBuffer);

         // Convert DBTYPE_CY values to string 
         pIDataConvert->DataConvert(DBTYPE_CY,   // wSrcType
            DBTYPE_STR,   // wDstType
            sizeof(LARGE_INTEGER),   // cbSrcLength 
            &cbDstLength,   // pcbDstLength
            &pBuffer[pBindings[0].obValue],   // pSrc
            strCurrency0,   // pDst
            sizeof(strCurrency0),   //cbDstMaxLength
            DBSTATUS_S_OK,   // dbsSrcStatus
            &dbsStatus,   // pdbsStatus
            0,   // bPrecision (used for DBTYPE_NUMERIC only)
            0,   // bScale (used for DBTYPE_NUMERIC only)
            DBDATACONVERT_DEFAULT);   // dwFlags

         pIDataConvert->DataConvert(DBTYPE_CY,   // wSrcType
            DBTYPE_STR,   // wDstType
            sizeof(LARGE_INTEGER),   // cbSrcLength 
            &cbDstLength,   // pcbDstLength
            &pBuffer[pBindings[1].obValue],   // pSrc
            strCurrency1,   // pDst
            sizeof(strCurrency1),   // cbDstMaxLength
            DBSTATUS_S_OK,   // dbsSrcStatus
            &dbsStatus,   // pdbsStatus
            0,   // bPrecision (used for DBTYPE_NUMERIC only)
            0,   // bScale (used for DBTYPE_NUMERIC only)
            DBDATACONVERT_DEFAULT); // dwFlags

         // Print cost and price values.
         printf("%-40s%s\n", strCurrency0, strCurrency1); //sparra
      };

      // Release the rows retrieved.
      pIRowset->ReleaseRows(lNumRowsRetrieved, hRows, NULL, NULL, NULL);

      // Get the next set of 10 rows.
      pIRowset->GetNextRows(NULL, 0, 10, &lNumRowsRetrieved, &pRows);
   }

   // Free up all allocated memory.
   delete [] pBuffer;
   pIAccessor->ReleaseAccessor(hAccessor, NULL);
   pIAccessor->Release();
   delete [] pBindings;

   return 0;
}

Fetch Rows from a Result Set (OLE DB)

Example

Description

Code

See Also

Concepts

Additional resources