how to use Readvariable() to read opc server data to client side

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C++

Visual-Studio

VS2010

After connecting with opc server, i m trying to directly use the defined function Readvariable() below to read server data to client side. Anyone know how to achieve this? Especially how to define the State pointer?

long COPCData::ReadVariable(LPCTSTR VariableName, VARIANT* Value, long* State, long TimeOut)
{
	long result;
	static BYTE parms[] =
		VTS_BSTR VTS_PVARIANT VTS_PI4 VTS_I4;
	InvokeHelper(0x10, DISPATCH_METHOD, VT_I4, (void*)&result, parms,
		VariableName, Value, State, TimeOut);
	return result;
}

long COPCData::WriteVariable(LPCTSTR VariableName, const VARIANT& Value, long TimeOut)
{
	long result;
	static BYTE parms[] =
		VTS_BSTR VTS_VARIANT VTS_I4;
	InvokeHelper(0x11, DISPATCH_METHOD, VT_I4, (void*)&result, parms,
		VariableName, &Value, TimeOut);
	return result;
}