Use HRESULT_FROM_WIN32.
Jun 262007
Jun 222007
Here is a sample to create an array of BSTR’s…
const long lCount = 100;
_bstr_t bstrArray[lCount];
COleSafeArray cosaSafeArray;
cosaSafeArray.CreateOneDim( VT_BSTR, lCount )
// Fill out this array
for( long lIndex = 0; lIndex < lCount; ++lIndex )
{
cosaSafeArray.PutElement( &lIndex,
static_cast<bstr>( bstrArray[lIndex] );
}
// Now you have a safe array of bstr's and since COleSafeArray
// is inherited from VARIANT you can directly use this safearray
// in COM calls with no overhead for freeing safe array
Use StringFromCLSID and CLSIDFromString.
Jun 042007
To enable the use of CLSID_MyClsid/IID_ISomeInterface while importing type libraries use…
#import "MyTypeLib.tlb" named_guids
Jun 042007
When importing a type library it could be at times cumbersome to use the default namespace name.
#import provides a nice option called rename_namespace.
Use…
#import "SomeTypelib.tlb" rename_namespace( "NibuNamespace" )
Using no_namespace is lazy programming 
. Namespaces reduces name collision hence usage should be encouraged.
Jun 042007
Sometime back I was wondering about whether there was a way to transfer our good ol’ NULL terminated strings using COM apart from using BSTR’s.
That’s how I bumped into “string” attribute provided by MIDL.
Here is how we use it…
typedef [string] char NormalString[1024]; [id(1), helpstring( "Displays null terminated UNICODE strings" )] HRESULT ShowMsgUnicodeString( [in,string] wchar_t* wCharString_i ); [id(2), helpstring( "Displays null terminated ANSI strings" )] HRESULT ShowMsgAnsiString( [in,string] char* cString_i );
Well if we don’t specify “string” then MIDL treats the parameter as an address of a wchar/char.
Callers can invoke the call as they would normally do with a function.
May 302007
Easiest way to construct a COM interface from it’s co class.
ISomeInterfacePtr sipPtr;
HRESULT hRes =
CComCreator< CComObject< CSomeCoClass > >::CreateInstance( 0,
IID_ISomeInterface,
reinterpret_cast( void**, &sipPtr ));
ASSERT( SUCCEEDED( hRes ));
Must be an ATL/COM Project.
