GetRows 方法示例 (VC++)
此示例使用 GetRows 方法从 Recordset 中检索指定数量的行，并使用结果数据填充数组。 在以下两种情况下，GetRows 方法将返回少于所需的行数：已到达 EOF，或者 GetRows 尝试检索已被其他用户删除的记录。 仅当出现第二种情况时，该函数才返回 False。 此过程需要 GetRowsOK 函数才能运行。
示例
// BeginGetRowsCpp.cpp
// compile with: /EHsc
#import "msado15.dll" no_namespace rename("EOF", "EndOfFile")
#include <stdio.h>
#include <ole2.h>
#include <conio.h>
// Function Declarations
inline void TESTHR(HRESULT x) { if FAILED(x) _com_issue_error(x); };
void GetRowsX();
bool GetRowsOK(_RecordsetPtr pRstTemp, int intNumber, _variant_t& avarData);
void PrintProviderError(_ConnectionPtr pConnection);
void PrintComError(_com_error &e);
int main() {
if (FAILED(::CoInitialize(NULL)))
return -1;
GetRowsX();
::CoUninitialize();
}
void GetRowsX() {
HRESULT hr = S_OK;
// Define string variables.
_bstr_t strCnn("Provider='sqloledb'; Data Source='My_Data_Source'; Initial Catalog='pubs'; Integrated Security='SSPI';");
// Define ADO object pointers, initialize pointers on define.
// These are in the ADODB:: namespace.
_RecordsetPtr pRstEmployees = NULL;
try {
// Open recordset with names and hire dates from employee table.
TESTHR(pRstEmployees.CreateInstance(__uuidof(Recordset)));
pRstEmployees->Open("SELECT fName, lName, hire_date "
"FROM Employee ORDER BY lName",strCnn, adOpenStatic, adLockReadOnly, adCmdText);
while (true) { // continuous loop
int intLines = 0;
// Get user input for number of rows.
printf("Enter number of rows to retrieve (0 to exit): ");
int intRows;
scanf_s("%d", &intRows);
if (intRows <= 0)
break;
// If GetRowsOK is successful, print the results,
// noting if the end of the file was reached.
_variant_t avarRecords;
if (GetRowsOK(pRstEmployees, intRows, avarRecords)) {
long lUbound;
HRESULT hr = SafeArrayGetUBound(avarRecords.parray, 2, &lUbound);
if (hr == 0) {
if (intRows > lUbound + 1) {
printf("\n(Not enough records in Recordset to retrieve %d rows)\n", intRows);
}
}
printf("%d record(s) found.\n", lUbound + 1);
// Print the retrieved data.
for (int intRecords = 0 ; intRecords < lUbound+1 ; intRecords++) {
long rgIndices[2];
rgIndices[0] = 0;
rgIndices[1] = intRecords;
_variant_t result;
result.vt = VT_BSTR;
hr = SafeArrayGetElement(avarRecords.parray, rgIndices, &result);
if (hr == 0)
printf("%s ",(LPCSTR)(_bstr_t)result);
rgIndices[0] = 1;
hr = SafeArrayGetElement(avarRecords.parray, rgIndices, &result);
if (hr == 0)
printf("%s, ",(LPCSTR)(_bstr_t)result);
rgIndices[0] = 2;
hr = SafeArrayGetElement(avarRecords.parray, rgIndices, &result);
if (hr == 0)
printf("%s\n", (LPCSTR)(_bstr_t)result);
intLines ++;
if (intLines % 10 == 0) {
printf("\nPress any key to continue...");
_getch();
intLines = 0;
system("cls");
}
}
printf("\n");
}
else {
// Assume GetRows error caused by another user's data changes,
// use Requery to refresh the Recordset and start over.
printf("GetRows failed--retry?\n");
char chKey;
do {
chKey = _getch();
} while (toupper(chKey) != 'Y' && toupper(chKey) != 'N');
if (toupper(chKey) == 'Y')
pRstEmployees->Requery(adOptionUnspecified);
else {
printf("GetRows failed!\n");
break;
}
}
// Because using GetRows leaves the current record pointer at the last record
// accessed, move the pointer back to the beginning of the Recordset before
// looping back for another search.
pRstEmployees->MoveFirst();
}
}
catch(_com_error &e) {
// Notify the user of errors if any.
// Pass a connection pointer accessed from the Recordset.
_variant_t vtConnect = pRstEmployees->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.
if (pRstEmployees)
if (pRstEmployees->State == adStateOpen)
pRstEmployees->Close();
}
bool GetRowsOK(_RecordsetPtr pRstTemp,int intNumber, _variant_t& avarData) {
// Store results of GetRows method in array.
avarData = pRstTemp->GetRows(intNumber);
// Return False only if fewer than the desired number of rows were returned,
// but not because the end of the Recordset was reached.
long lUbound;
HRESULT hr = SafeArrayGetUBound(avarData.parray, 2, &lUbound);
if (hr == 0) {
if ((intNumber > lUbound + 1) && (!(pRstTemp->EndOfFile)))
return false;
else
return true;
}
else {
printf ("\nUnable to Get the Array's Upper Bound\n");
return false;
}
}
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, (LPCSTR) 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);
}
输入
2
0
示例输出
2 record(s) found.
Paolo Accorti, 8/27/1992
Pedro Afonso, 12/24/1990