socket连接超时判断

select 方式
判断m_server的m_port端口是否可以连上，超时限制为nTimeOut秒
BOOL ConnectTest(char * m_server,int m_port)
{

struct hostent* host = NULL;
struct sockaddr_in saddr;
unsigned int s = 0;
BOOL ret;
time_t start;
int error;
host = gethostbyname (m_server);
if (host==NULL)return FALSE;

saddr.sin_family = AF_INET;
saddr.sin_port = htons(m_port);
saddr.sin_addr = *((struct in_addr*)host->h_addr);

if( (s=socket(AF_INET, SOCK_STREAM, 0))<0){
return FALSE;
}

fcntl(s,F_SETFL, O_NONBLOCK);

if(connect(s,(struct sockaddr*)&saddr, sizeof(saddr)) == -1) {
if (errno == EINPROGRESS){// it is in the connect process
struct timeval tv;
fd_set writefds;
tv.tv_sec = m_nTimeOut;
tv.tv_usec = 0;
FD_ZERO(&writefds);
FD_SET(s, &writefds);
if(select(s+1,NULL,&writefds,NULL,&tv)>0){
int len=sizeof(int);
//下面的一句一定要，主要针对防火墙
getsockopt(s, SOL_SOCKET, SO_ERROR, &error, &len);
if(error==0) ret=TRUE;
else ret=FALSE;
}else ret=FALSE;//timeout or error happen
}else ret=FALSE;
}
else ret=TRUE;

close(s);
return ret;
}