The following code example demonstrates how to retreive data.
Create a Command object:
ICommandText* pICommandText; hr = pIDBCreateCommand->CreateCommand( NULL, IID_ICommandText, (IUnknown**)&pICommandText);
Set the SQL statement:
hr = pICommandText->SetCommandText( DBGUID_DBSQL, L"SELECT * FROM testReadStringData");
Create and describe the rowset data structure. This structure contains fields for each column you want accessed, as shown:
IAccessor* pIAccessor;
hr = pICommandText->QueryInterface(IID_IAccessor, (void**)&pIAccessor);
static DBBINDING ExactBindings [1] = {
{
1, // iOrdinal
offsetof (ExactlyTheSame,s), // obValue
0, // No length binding
0, // No Status binding
NULL, // No TypeInfo
NULL, // No Object
NULL, // No Extensions
DBPART_VALUE,
DBMEMOWNER_CLIENTOWNED, // Ignored
DBPARAMIO_NOTPARAM,
sizeof(mystr), // number of bytes
0,
DBTYPE_WSTR | DBTYPE_BYREF,
0, // No Precision
0 // No Scale
}
};
DBBINDSTATUS status[1];
HACCESSOR hAccessor;
HRESULT hr = pIAccessor->CreateAccessor(
DBACCESSOR_ROWDATA, 1, ExactBindings,
sizeof(ExactlyTheSame), &hAccessor, status);
pIAccessor->Release();
Execute the rowset:
DBROWCOUNT cRowsAffected; IRowset* pIRowset; hr = pICommandText->Execute( NULL, IID_IRowset, params, &cRowsAffected, (IUnknown**)&pIRowset);
The following code demonstrates getting the rows one at a time:
DBCOUNTITEM cRowsReturned; HROW hRow[1]; HROW* pRow = hRow; hr = pIRowset->GetNextRows(NULL, 0, 1, &cRowsReturned, &pRow);
Use IMalloc to free the memory allocated by GetData:
CComPtr<IMalloc> pIMalloc = NULL;
hr = CoGetMalloc( MEMCTX_TASK, &pIMalloc );
while (hr == S_OK)
{
Retrieve the data for the specified row:
ExactlyTheSame pData[1] = { {NULL} };
hr = pIRowset->GetData(hRow[0], hAccessor, pData);
wchar_t* value = pData[0].s;
Free the allocated memory:
// client owned memory must be freed by the client pIMalloc->Free(pData[0].s); pData[0].s = NULL;
Release the rows:
hr = pIRowset->ReleaseRows(1, pRow, NULL, NULL, NULL);
Get the next row:
hr = pIRowset->GetNextRows(NULL, 0, 1, &cRowsReturned, &pRow); } pIRowset->Release(); pICommandText->Release();
To retrieve rows from a database, execute a SELECT statement using ICommandText::Execute. This opens a cursor on the statement. You then use IRowset::GetNextRows to fetch rows through the cursor. When an application frees the statement by releasing the rowset, it closes the cursor.
