ATL uses CComPtr and CComQIPtr to manage COM interface pointers. Both are derived from CComPtrBase, and both perform automatic reference counting.
The CComPtr and CComQIPtr classes can help eliminate memory leaks by performing automatic reference counting. The following functions both perform the same logical operations; however, note how the second version may be less error-prone by using the CComPtr class:
// Error-checking routine that performs manual lifetime management
// of a COM IErrorInfo object
HRESULT CheckComError_Manual()
{
HRESULT hr;
CComBSTR bstrDescription;
CComBSTR bstrSource;
CComBSTR bstrHelpFile;
IErrorInfo* pErrInfo = NULL; // naked COM interface pointer
hr = ::GetErrorInfo( 0, &pErrInfo );
if( hr != S_OK )
return hr;
hr = pErrInfo->GetDescription( &bstrDescription );
if( FAILED( hr ) )
{
pErrInfo->Release(); // must release interface pointer before returning
return hr;
}
hr = pErrInfo->GetSource( &bstrSource );
if( FAILED( hr ) )
{
pErrInfo->Release(); // must release interface pointer before returning
return hr;
}
hr = pErrInfo->GetHelpFile( &bstrHelpFile );
if( FAILED( hr ) )
{
pErrInfo->Release(); // must release interface pointer before returning
return hr;
}
pErrInfo->Release(); // must release interface pointer before returning
return S_OK;
}// Error-checking routine that performs automatic lifetime management
// of a COM IErrorInfo object through a CComPtr smart pointer object
HRESULT CheckComError_SmartPtr()
{
HRESULT hr;
CComBSTR bstrDescription;
CComBSTR bstrSource;
CComBSTR bstrHelpFile;
CComPtr<IErrorInfo> pErrInfo;
hr = ::GetErrorInfo( 0, &pErrInfo );
if( hr != S_OK )
return hr;
hr = pErrInfo->GetDescription( &bstrDescription );
if( FAILED( hr ) )
return hr;
hr = pErrInfo->GetSource( &bstrSource );
if( FAILED( hr ) )
return hr;
hr = pErrInfo->GetHelpFile( &bstrHelpFile );
if( FAILED( hr ) )
return hr;
return S_OK;
} // CComPtr will auto-release underlying IErrorInfo interface pointer as neededIn Debug builds, link atlsd.lib for code tracing.