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This example demonstrates the DefinedSize property of a Column. The code will redefine the size of the FirstName column of the Employees table of the Northwind database. Then, the change in the values of the FirstName Field of a Recordset based on the Employees table is displayed. Note that by default, the FirstName field becomes padded with spaces after you redefine the DefinedSize property.
// BeginDefinedSizeCpp.cpp
// compile with: /EHsc
#import "msado15.dll" rename("EOF", "EndOfFile")
#import "msadox.dll" no_namespace
#include "iostream"
using namespace std;
inline void TESTHR(HRESULT x) {if FAILED(x) _com_issue_error(x);};
int main() {
if ( FAILED(::CoInitialize(NULL)) )
return -1;
HRESULT hr = S_OK;
// Define ADOX object pointers, initialize pointers. These are in the ADODB namespace.
_CatalogPtr m_pCatNorthwind = NULL;
_ColumnPtr m_pColFirstName = NULL;
_ColumnPtr m_pColNewFirstName = NULL;
// Define ADODB object pointers
ADODB::_RecordsetPtr m_pRstEmployees = NULL;
// Define string variables.
_bstr_t strCnn("Provider='Microsoft.JET.OLEDB.4.0';data source='c:\\Northwind.mdb';");
_bstr_t aryFirstName[10];
try {
// Open a Recordset for the Employees table.
TESTHR(hr = m_pRstEmployees.CreateInstance(__uuidof(ADODB::Recordset)));
TESTHR(hr = m_pCatNorthwind.CreateInstance(__uuidof (Catalog)));
TESTHR(hr = m_pColNewFirstName.CreateInstance(__uuidof(Column)));
m_pRstEmployees->Open("Employees", strCnn,ADODB::adOpenKeyset, ADODB::adLockReadOnly, ADODB::adCmdTable);
long lngSize = m_pRstEmployees->RecordCount;
aryFirstName[lngSize];
// Open a catalog for the Northwind database, using same connection as rstEmployees.
m_pCatNorthwind->PutActiveConnection(m_pRstEmployees->GetActiveConnection());
// Loop through the recordset displaying the contents, of the FirstName field, the field's defined size,
// and its actual size. Also store FirstName values in aryFirstName array.
m_pRstEmployees->MoveFirst();
printf("\nOriginal Defined Size and Actual Size");
int iCount = 0;
while (!(m_pRstEmployees->EndOfFile)) {
printf("\nEmployee Name:");
printf("%s ", (LPSTR)(_bstr_t)m_pRstEmployees->Fields->GetItem("FirstName")->Value);
printf("%s\n", (LPSTR)(_bstr_t)m_pRstEmployees->Fields->GetItem("LastName")->Value);
printf(" FirstName Defined size: %d\n", m_pRstEmployees->Fields->GetItem("FirstName")->DefinedSize);
printf(" FirstName Actual size: %d\n", m_pRstEmployees->Fields->GetItem("FirstName")->ActualSize);
aryFirstName[iCount] = (_bstr_t) m_pRstEmployees->Fields->GetItem("FirstName")->Value;
m_pRstEmployees->MoveNext();
}
m_pRstEmployees->Close();
// Redefine the DefinedSize of FirstName in the catalog.
m_pColFirstName = m_pCatNorthwind->Tables->GetItem("Employees")->Columns->GetItem("FirstName");
m_pColNewFirstName->Name = m_pColFirstName->Name;
m_pColNewFirstName->Type = m_pColFirstName->Type;
m_pColNewFirstName->DefinedSize = (m_pColFirstName->DefinedSize) + 1;
// Append new FirstName column to catalog.
m_pCatNorthwind->Tables->GetItem("Employees")->Columns->Delete(m_pColFirstName->Name);
m_pCatNorthwind->Tables->GetItem("Employees")->Columns->Append(_variant_t((IDispatch*)m_pColNewFirstName, true),
adVarWChar,
m_pColNewFirstName->DefinedSize);
// Open Employee table in Recordset for updating.
m_pRstEmployees->Open("Employees",
m_pCatNorthwind->GetActiveConnection(),
ADODB::adOpenKeyset,
ADODB::adLockOptimistic,
ADODB::adCmdTable);
// Loop through the recordset displaying the contents of the FirstName field,the field's defined size,
// and its actual size. Also restore FirstName values from aryFirstName.
m_pRstEmployees->MoveFirst();
printf("\n\nNew Defined Size and Actual Size");
iCount = 0;
while (!(m_pRstEmployees->EndOfFile)) {
m_pRstEmployees->Fields->GetItem("FirstName")->Value = aryFirstName[iCount];
printf("\nEmployee Name: ");
printf("%s ", (LPSTR) (_bstr_t)m_pRstEmployees->Fields->GetItem("FirstName")->Value);
printf("%s\n", (LPSTR)(_bstr_t)m_pRstEmployees->Fields->GetItem("LastName")->Value);
printf(" FirstName Defined size: %d\n", m_pRstEmployees->Fields->GetItem("FirstName")->DefinedSize);
printf(" FirstName Actual size: %d\n", m_pRstEmployees->Fields->GetItem("FirstName")->ActualSize);
m_pRstEmployees->MoveNext();
}
m_pRstEmployees->Close();
// Restore original FirstName column to catalog
m_pCatNorthwind->Tables->GetItem("Employees")->Columns->Delete(m_pColNewFirstName->Name);
m_pCatNorthwind->Tables->GetItem("Employees")->Columns->Append(_variant_t((IDispatch*)m_pColFirstName,
true),
adVarWChar,
m_pColFirstName->DefinedSize);
// Restore original FirstName values to Employees table.
m_pRstEmployees->Open("Employees",
m_pCatNorthwind->GetActiveConnection(),
ADODB::adOpenKeyset,
ADODB::adLockOptimistic,
ADODB::adCmdTable);
m_pRstEmployees->MoveFirst();
iCount = 0;
while ( !(m_pRstEmployees->EndOfFile) ) {
m_pRstEmployees->Fields->GetItem("FirstName")->Value = aryFirstName[iCount];
m_pRstEmployees->MoveNext();
iCount++;
}
}
catch(_com_error &e) {
// Notify the user of errors if any.
_bstr_t bstrSource(e.Source());
_bstr_t bstrDescription(e.Description());
printf("\n\tSource : %s \n\tdescription : %s \n ", (LPCSTR)bstrSource, (LPCSTR)bstrDescription);
}
catch(...) {
cout << "Error occurred in DefinedSizeX...." << endl;
}
if (m_pRstEmployees)
if (m_pRstEmployees->State == 1)
m_pRstEmployees->Close();
m_pCatNorthwind = NULL;
::CoUninitialize();
}