Question

MFC使用ADO数据集指针,如何遍历所有字段?如果我不知道字段名的情况下.

我想要获取的内容，该数据集的列数，以及当前记录行下各字段中的值。比如，我定义一个_RecordSetPtr 的指针precord1。可不可以由索引号什么的来访问各个字段的值呢？

Answer 1

Value 属性范例 (VC++)

本范例通过显示 Employees 表的字段和属性值来演示 Field 和 Property 对象的 Value 属性。

#import "c:\Program Files\Common Files\System\ADO\msado15.dll" \
no_namespace rename("EOF", "EndOfFile")

#include <ole2.h>
#include <stdio.h>
#include <conio.h>

// Function declarations
inline void TESTHR(HRESULT x) {if FAILED(x) _com_issue_error(x);};
void ValueX(void);
void PrintProviderError(_ConnectionPtr pConnection);
void PrintComError(_com_error &e);

//////////////////////////////////////////////////////////
// //
// Main Function //
// //
//////////////////////////////////////////////////////////

void main()
{
if(FAILED(::CoInitialize(NULL)))
return;

ValueX();

::CoUninitialize();
}

//////////////////////////////////////////////////////////
// //
// ValueX Function //
// //
//////////////////////////////////////////////////////////
void ValueX(void)
{
HRESULT hr = S_OK;

// Define string variables.
_bstr_t strCnn("Provider=sqloledb;Data Source=srv;"
"Initial Catalog=Pubs;User Id=sa;Password=;");

// Define ADO object pointers.
// Initialize pointers on define.
// These are in the ADODB:: namespace.
_RecordsetPtr pRstEmployees = NULL;
FieldsPtr pFldLoop = NULL;
PropertiesPtr pPrpLoop = NULL;
_variant_t vtIndex;
vtIndex.vt = VT_I2;

try
{
// Open recordset with data from Employees table.
TESTHR(pRstEmployees.CreateInstance(__uuidof(Recordset)));
pRstEmployees->Open ("Employees",strCnn ,
adOpenForwardOnly, adLockReadOnly, adCmdTable);

printf("Field values in rstEmployees\n\n");

// Enumerate the Fields collection of the Employees table.
pFldLoop = pRstEmployees->GetFields();

for (int intFields = 0; intFields < (int)pFldLoop->
GetCount(); intFields++)
{
vtIndex.iVal = intFields;

// Because Value is the default property of a
// Field object,the use of the actual keyword
// here is optional.
printf(" %s = %s\n\n" ,
(LPCSTR) pFldLoop->GetItem(vtIndex)->GetName(),
(LPCSTR) (_bstr_t) pFldLoop->GetItem(vtIndex)->Value);
}

printf("Press any key to continue...\n\n");
getch();
printf("Property values in rstEmployees\n\n");

// Enumerate the Properties collection of the Recordset object.
pPrpLoop = pRstEmployees->GetProperties();
int intLine = 0;

for (int intProperties = 0; intProperties < (int)pPrpLoop->
GetCount(); intProperties++)
{
vtIndex.iVal = intProperties;

// Because Value is the default property of a
// Property object,the use of the actual keyword
// here is optional.
_variant_t propValue = pPrpLoop->GetItem(vtIndex)->Value;
switch(propValue.vt)
{

case (VT_BOOL):
if(propValue.boolVal)
{
printf(" %s = True\n\n",(LPCSTR) pPrpLoop->
GetItem(vtIndex)->GetName());
}
else
{
printf(" %s = False\n\n",(LPCSTR) pPrpLoop->
GetItem(vtIndex)->GetName());
}
break;

case (VT_I4):
printf(" %s = %d\n\n",(LPCSTR) pPrpLoop->
GetItem(vtIndex)->GetName(),
pPrpLoop->GetItem(vtIndex)->Value.lVal);
break;

case (VT_EMPTY):
printf(" %s = \n\n",(LPCSTR) pPrpLoop->
GetItem(vtIndex)->GetName());
break;

default:
break;
}

intLine++;
if (intLine % 10 == 0)
{
printf("\nPress any key to continue...");
getch();

//Clear the screen for the next display
system("cls");
}
}

pRstEmployees->Close();
}

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 occured.");
break;
}
}
}

//////////////////////////////////////////////////////////
// //
// PrintProviderError Function //
// //
//////////////////////////////////////////////////////////
void PrintProviderError(_ConnectionPtr pConnection)
{
// Print Provider Errors from Connection object.
// pErr is a record object in the Connection’s Errors 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("Error number: %x\t%s\n", pErr->Number,
(LPCSTR) pErr->Description);
}
}
}

//////////////////////////////////////////////////////////
// //
// PrintComError Function //
// //
//////////////////////////////////////////////////////////
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);
}