setsockopt()设置TTL问题

[white3snow]

int bread=setsockopt(sockraw,IPPROTO_IP,IP_TTL,(char*)&ttl,sizeof(int));

为什么编译会出现：'IP_TTL' : undeclared identifier

[Wenxy1]

Requirements
Windows NT/2000/XP: Included in Windows NT 3.1 and later.
Windows 95/98/Me: Included in Windows 95 and later.
Header: Declared in Winsock2.h.
Library: Use Ws2_32.lib.

[UDX协议]

#include "ws2tcpip.h"
int ttl = 255;
int ret = setsockopt(m_socket, IPPROTO_IP,IP_TTL, (char*)&ttl, sizeof(ttl));