Visual C++ 扩展示例
此程序显示如何从字段检索值并将其转换为 C/C++ 变量。
此示例还利用“智能指针”,该指针自动处理调用 QueryInterface
和 IADORecordBinding 接口的引用计数的特定于 COM 的详细信息。
如果没有智能指针,可以编写以下代码:
IADORecordBinding *picRs = NULL;
...
TESTHR(pRs->QueryInterface(
__uuidof(IADORecordBinding), (LPVOID*)&picRs));
...
if (picRs) picRs->Release();
通过智能指针,可以使用以下语句从 IADORecordBinding
接口派生 IADORecordBindingPtr
类型:
_COM_SMARTPTR_TYPEDEF(IADORecordBinding, __uuidof(IADORecordBinding));
并按如下所示实例化指针:
IADORecordBindingPtr picRs(pRs);
由于 Visual C++ 扩展由 Recordset 对象实现,因此智能指针 picRs
的构造函数采用 _RecordsetPtr
指针 pRs
。 构造函数使用 pRs
调用 QueryInterface
以查找 IADORecordBinding
接口。
// Visual_Cpp_Extensions_Example.cpp
// compile with: /EHsc
#import "msado15.dll" no_namespace rename("EOF", "EndOfFile")
#include <icrsint.h>
_COM_SMARTPTR_TYPEDEF(IADORecordBinding, __uuidof(IADORecordBinding));
inline void TESTHR(HRESULT _hr) { if FAILED(_hr) _com_issue_error(_hr); }
class CCustomRs : public CADORecordBinding {
BEGIN_ADO_BINDING(CCustomRs)
ADO_VARIABLE_LENGTH_ENTRY2(2, adVarChar, m_ch_fname, sizeof(m_ch_fname), m_ul_fnameStatus, false)
ADO_VARIABLE_LENGTH_ENTRY2(4, adVarChar, m_ch_lname, sizeof(m_ch_lname), m_ul_lnameStatus, false)
END_ADO_BINDING()
public:
CHAR m_ch_fname[22];
CHAR m_ch_lname[32];
ULONG m_ul_fnameStatus;
ULONG m_ul_lnameStatus;
};
int main() {
::CoInitialize(NULL);
try {
_RecordsetPtr pRs("ADODB.Recordset");
CCustomRs rs;
IADORecordBindingPtr picRs(pRs);
pRs->Open(L"SELECT * FROM Employee ORDER BY lname", L"dsn=DataPubs;Trusted_Connection=yes;", adOpenStatic, adLockOptimistic, adCmdText);
TESTHR(picRs->BindToRecordset(&rs));
while (!pRs->EndOfFile) {
// Process data in the CCustomRs C++ instance variables.
printf("Name = %s %s\n",
(rs.m_ul_fnameStatus == adFldOK ? rs.m_ch_fname: "<Error>"),
(rs.m_ul_lnameStatus == adFldOK ? rs.m_ch_lname: "<Error>") );
// Move to the next row of the Recordset. Fields in the new row will
// automatically be placed in the CCustomRs C++ instance variables.
pRs->MoveNext();
}
}
catch (_com_error &e ) {
printf("Error:\n");
printf("Code = %08lx\n", e.Error());
printf("Meaning = %s\n", e.ErrorMessage());
printf("Source = %s\n", (LPCSTR) e.Source());
printf("Description = %s\n", (LPCSTR) e.Description());
}
::CoUninitialize();
}