如何获取服务器时间

如何使用C++程序获取一个固定的服务器的时间，比如www.baidu.com的时间

// 思路是发送一个http请求，然后从response字符串里截取出Date部分，这样得到的时间是GMT格式的，不过转本地时间也很容易了

#include <winsock2.h>
#include <ws2tcpip.h>
#include <stdio.h>

#pragma comment(lib, "ws2_32.lib")

int main()
{
WSADATA wsaData;
addrinfo hints, *rs;
sockaddr_in serveraddr;
SOCKET s;
char host[256], hostIP[256], request[1024], *p;
int rc, nBytes;

WSAStartup(MAKEWORd(2, 2), &wsaData);
s = socket(AF_INET, SOCK_STREAM, IPPROTO_TCP);

printf("plz input host name(eg.www.example.com):");
gets(host);
ZeroMemory(&hints, sizeof(addrinfo));
hints.ai_flags = AI_PASSIVE;
hints.ai_family = AF_UNSPEC;
hints.ai_socktype = SOCK_STREAM;
hints.ai_protocol = IPPROTO_TCP;

rc = getaddrinfo(host, "80", &hints, &rs);

if(rc != 0) {
printf("getaddrinfo failed with error code:%d\n", WSAGetLastError());
goto clean;
}

getnameinfo(rs->ai_addr, rs->ai_addrlen, hostIP, NI_MAXHOST, NULL, 0, NI_NUMERICHOST);
printf("server ip is: %s\n", hostIP);
freeaddrinfo(rs);

serveraddr.sin_family = AF_INET;
serveraddr.sin_addr.s_addr = inet_addr(hostIP);
serveraddr.sin_port = htons(80);

rc = connect(s, (SOCKADDR*) &serveraddr, sizeof(serveraddr));
if(rc != 0) {
printf("connect to server failed.");
goto clean;
}

strcpy(request, "GET / HTTP/1.1\r\n");
strcat(request, "Host: ");
strcat(request, host);
strcat(request, "\r\nConnection: close\r\n\r\n");
send(s, request, strlen(request), 0);
while(1)
{
nBytes = recv(s, request, 1024, 0);
if(nBytes == SOCKET_ERROR)
{
printf("recv failed with error %d\n",WSAGetLastError());
goto clean;
} else {
p = strstr(request, "Date:");
p += 5;
while(*p == ' ') ++p;
printf("server time: ");
while(*p != '\r')
putchar(*p++);
putchar('\n');
break;
}

}
clean:
closesocket(s);
WSACleanup();
return 0;
}

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