How to use ?

I have this class

#include "WebSocket.h"


WebSocket::WebSocket(void) {
     WINHTTP_WEB_SOCKET_BUFFER_TYPE eBufferType;
}


WebSocket::~WebSocket(void) {
}

and the header file

#pragma once
#include <WinSock2.h>
#include <windows.h>
#include <winhttp.h>

#pragma once
class WebSocket {
public:
	WebSocket(void);
	~WebSocket(void);
};

when I try to complile it in Visual Sudio 2010 I have this error:

1>WebSocket.cpp(6): error C2065: 'WINHTTP_WEB_SOCKET_BUFFER_TYPE' : undeclared identifier

I have Win SDK and the file itself installed.

Can anyone please explain me how to fix it?

Thank you!