DefinedSize-Eigenschaft (Beispiel) (VC++)

In diesem Beispiel wird die eigenschaft DefinedSize eines Columnveranschaulicht. Der Code definiert die Größe der Spalte "Vorname" der Tabelle Employees der Datenbank Northwind neu. Anschließend wird die Änderung der Werte des "FirstName"-Feld- eines Recordset basierend auf der tabelle Employees angezeigt. Beachten Sie, dass das Feld "Vorname" standardmäßig mit Leerzeichen aufgefüllt wird, nachdem Sie die eigenschaft DefinedSize neu definiert haben.

// 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();  
}  

Siehe auch

Column-Objekt (ADOX)
DefinedSize-Eigenschaft (ADOX)