Seek (méthode) et Index (propriété), exemple (VC++)

Cet exemple utilise la méthode Chercher de l’objet Recordset et la propriété Index conjointement avec un ID d’employé donné pour localiser le nom de l’employé dans la table Employés de la base de données Nwind.mdb.

// BeginSeekCpp.cpp  
// compile with: /EHsc  
#import "msado15.dll" no_namespace rename("EOF", "EndOfFile")  
  
#include <stdio.h>  
#include <ole2.h>  
#include <conio.h>  
#include <string.h>  
#include "icrsint.h"  
  
// Class extracts only EmployeeId,FirstName and LastName from employees table  
class CEmployeeRs : public CADORecordBinding {  
   BEGIN_ADO_BINDING(CEmployeeRs)  
  
   // Column hiredate is the 1st field in the table.  
   ADO_VARIABLE_LENGTH_ENTRY2(1, adInteger,m_ie_empid, sizeof(m_ie_empid),   
                              le_empidStatus, FALSE)  
  
   // Column LastName is the 2nd field in the table.  
   ADO_VARIABLE_LENGTH_ENTRY2(2, adVarChar, m_sze_lname, sizeof(m_sze_lname),   
                             le_lnameStatus, FALSE)  
  
   // Column FirstName is the 3rd field in the table.  
   ADO_VARIABLE_LENGTH_ENTRY2(2, adVarChar, m_sze_fname, sizeof(m_sze_fname),   
                             le_fnameStatus, FALSE)  
   END_ADO_BINDING()  
  
public:  
   INT m_ie_empid;  
   ULONG le_empidStatus;  
   CHAR m_sze_fname[11];  
   ULONG le_fnameStatus;  
   CHAR m_sze_lname[21];  
   ULONG le_lnameStatus;      
};  
  
// Function declarations  
inline void TESTHR(HRESULT x) { if FAILED(x) _com_issue_error(x); };  
void SeekX();  
void PrintProviderError(_ConnectionPtr pConnection);  
void PrintComError(_com_error &e);  
  
inline char* mygets(char* strDest, int n) {      
   char strExBuff[10];  
   char* pstrRet = fgets(strDest, n, stdin);  
  
   if (pstrRet == NULL)  
      return NULL;  
  
   if (!strrchr(strDest, '\n'))  
      // Exhaust the input buffer.  
      do {  
         fgets(strExBuff, sizeof(strExBuff), stdin);  
      } while (!strrchr(strExBuff, '\n'));  
   else  
      // Replace '\n' with '\0'  
      strDest[strrchr(strDest, '\n') - strDest] = '\0';  
  
   return pstrRet;  
}  
  
int main() {  
   if (FAILED(::CoInitialize(NULL)))  
      return -1;  
  
   SeekX();  
   ::CoUninitialize();  
}  
  
void SeekX() {  
   HRESULT hr = S_OK;  
  
   // Define ADO object pointers, initialize pointers on define. These are in the ADODB::  namespace.  
   _RecordsetPtr pRstEmp = NULL;  
  
   IADORecordBinding *picRs = NULL;   // Interface Pointer declared  
   CEmployeeRs EmpRs;   // C++ class object  
  
   // Definitions of other variables  
   _bstr_t strPrompt("Enter an EmployeeID (e.g., 1 to 9)");  
   char strEmpId[2];  
  
   try {  
      TESTHR(pRstEmp.CreateInstance(__uuidof(Recordset)));  
      pRstEmp->CursorLocation = adUseServer;  
      pRstEmp->Open("employees", "Provider='Microsoft.Jet.OLEDB.4.0';"   
         "Data Source='C:\\Program Files\\Microsoft Office\\Office\\"  
         "Samples\\Northwind.mdb';",  
         adOpenKeyset,adLockReadOnly,adCmdTableDirect);  
  
      // Open an IADORecordBinding interface pointer which   
      // we'll use for binding Recordset to a Class    
      TESTHR(pRstEmp->QueryInterface(__uuidof(IADORecordBinding), (LPVOID*)&picRs));  
  
      // Bind the Recordset to a C++ Class  
      TESTHR(picRs->BindToRecordset(&EmpRs));  
  
      // Does this provider support Seek and Index?  
      if (pRstEmp->Supports(adIndex) && pRstEmp->Supports(adSeek)) {  
         pRstEmp->Index = "PrimaryKey";  
  
         // Display all the employees.  
         pRstEmp->MoveFirst();  
         while (!pRstEmp->EndOfFile) {  
            printf("%d : %s %s\n",    
               EmpRs.le_empidStatus == adFldOK ?   
               EmpRs.m_ie_empid : 0,   
               EmpRs.le_fnameStatus == adFldOK ?   
               EmpRs.m_sze_fname : "<NULL>",   
               EmpRs.le_lnameStatus == adFldOK ?   
               EmpRs.m_sze_lname : "<NULL>");  
  
            pRstEmp->MoveNext();  
         }  
         // Prompt the user for an EmployeeID between 1 and 9.  
         do {  
            pRstEmp->MoveFirst();  
            printf("\n\n%s\t",(LPCSTR) strPrompt);  
            mygets(strEmpId, 2);  
  
            // Quit if strEmpID is a zero-length string (CANCEL, null, etc.)  
            char *strTemp = strtok_s(strEmpId," \t", NULL);  
            if (strTemp == NULL) break;  
            if (strlen(strTemp) == 1 && atoi(strTemp) >= 1 && atoi(strTemp) <= 9) {  
               _variant_t strEmployeeId(strTemp);  
               pRstEmp->Seek(strEmployeeId, adSeekAfterEQ);  
               if (pRstEmp->EndOfFile)  
                  printf("Employee not found.\n");  
               else {  
                  printf("%d : Employee='%s %s'\n",    
                     EmpRs.le_empidStatus == adFldOK ?   
                     EmpRs.m_ie_empid : 0,  
                     EmpRs.le_fnameStatus == adFldOK ?   
                     EmpRs.m_sze_fname : "<NULL>",   
                     EmpRs.le_lnameStatus == adFldOK ?   
                     EmpRs.m_sze_lname : "<NULL>");  
               }  
            }  
         } while(true);  
      }    
   }  
   catch(_com_error &e) {  
      // Notify the user of errors if any.  
      // Pass a connection pointer accessed from the Recordset.  
      _variant_t vtConnect = pRstEmp->GetActiveConnection();  
  
      // GetActiveConnection returns connect string if connection  
      // is not open, else returns Connection object.  
      switch(vtConnect.vt) {  
         case VT_BSTR:  
            PrintComError(e);  
            break;  
         case VT_DISPATCH:  
            PrintProviderError(vtConnect);  
            break;  
         default:  
            printf("Errors occurred.");  
            break;  
      }  
   }  
  
   // Clean up objects before exit.  Release the IADORecordset Interface here     
   if (picRs)  
      picRs->Release();  
  
   if (pRstEmp)  
      if (pRstEmp->State == adStateOpen)  
         pRstEmp->Close();  
}  
  
void PrintProviderError(_ConnectionPtr pConnection) {  
   // Print Provider Errors from Connection object.  
   // pErr is a record object in the Connection's Error collection.  
   ErrorPtr pErr = NULL;  
  
   if ( (pConnection->Errors->Count) > 0) {  
      long nCount = pConnection->Errors->Count;  
  
      // Collection ranges from 0 to nCount -1.  
      for (long i = 0 ; i < nCount ; i++) {  
         pErr = pConnection->Errors->GetItem(i);  
         printf("\t Error number: %x\t%s", pErr->Number, pErr->Description);  
      }  
   }  
}  
  
void PrintComError(_com_error &e) {  
   _bstr_t bstrSource(e.Source());  
   _bstr_t bstrDescription(e.Description());  
  
   // Print COM errors.   
   printf("Error\n");  
   printf("\tCode = %08lx\n", e.Error());  
   printf("\tCode meaning = %s\n", e.ErrorMessage());  
   printf("\tSource = %s\n", (LPCSTR) bstrSource);  
   printf("\tDescription = %s\n", (LPCSTR) bstrDescription);  
}  

Voir aussi

Index, propriété
Recordset, objet (ADO)
Seek, méthode