C / C++ / MFC

try {
		_CommandPtr pCommand;
		_ParameterPtr pRetVal;

		pCommand.CreateInstance(__uuidof(Command));
		pCommand->ActiveConnection = m_pConn;
		pCommand->CommandText = "p_YourProc";
		pCommand->CommandType = adCmdStoredProc;
	
		// Create and add return value param
		pRetVal = pCommand->CreateParameter ( _bstr_t ("RETURN_VALUE"), adInteger, adParamReturnValue, 0);
		pCommand->Parameters->Append(pRetVal);

		// create and add taskid param
		pCommand->Parameters->Append ( pCommand->CreateParameter( _bstr_t ("YourParamIn"),adInteger,adParamInput,0 ,_variant_t(lTicketId)));
		pCommand->Execute(NULL, NULL, adCmdStoredProc);

                // this is the bit you're interested in
		lSuccess = (DWORD) pRetVal->GetValue();
	} catch (_com_error e)
	{
		//handle error
	}

Create Procedure MyProc 
@Param1 Integer,
@ParamRet varchar(100) output
AS
...
Select @ParamRect = "Hello World"
Go

Select @ParamRect = 'Hello World'