winSocket下有4个非阻塞的方式；
select模型是winSocket下最常见的i/o模型,通过select可以判断是否存在一个或多个有效的socket连接状态，判断套接字是否可以读取或者写入。他既能防止socket处于阻塞状态下时候，最后一次io操作以后进入阻塞状态，也可以套接字处于非阻塞状态下出现的wsaewouldblock错误，
select 函数原型：
int select ( int nfds, //用来与Berkely socket兼容， 通常写0 fd_set* readfds, //检查可读性的socket集合 fd_set* writefds, //检查可写性的socket集合 fd_set* exceptfds,//检查异常的socket集合 const struct timeval* timeout // 设置超时时间
);
返回值：
readfds, writefds, exceptfds中被检查复合条件的socket总数。
注意：
由于select每次返回时，readfds, writefds, exceptfds都会被改变，所以，下次调用select前，要重新初始化fds。
对于三种检查各自如下：
readfds:
> 若当前socket处在listen状态，则有个连接到来，调用accept将成功建立连接
>若连接已经建立，则意味着有新数据到来，此时可以调用recv接收数据
>对方连接终止，调用recv，根据返回值判断是否是正常终止： 0 对方正常终止， ErrorCode 对方重置连接或强制断开连接
writefds:
>当前socket调用了connect， 则成功连接
>当前socket调用了send，则能成功发送出去
exceptfds:
>当前socket调用connect，则连接失败
>OOB 数据可读（暂时没研究，OOB是什么个东东）
以下附上简单的测试代码：
设置socket为非阻塞模式的时候要先设置
int status = ioctlsocket（socket s，FIOBIO，&cmd）；
如果status 不等于socket_error表示非阻塞模式设置成功
server端代码：
#include "SocketInit.h"
#include "iostream"
using namespace std;
CInitSock sockInit;
int main()
{
SOCKET s = SocketFactory::getTCPSocket();
hostent *thisHost = gethostbyname("");
char *localIP = inet_ntoa (*(struct in_addr *)*thisHost->h_addr_list);
const int localIPInt = inet_addr(localIP);
const unsigned short linkPort = ntohs(4001);//本地监听
sockaddr_in servAddr;
servAddr.sin_family = AF_INET;
servAddr.sin_port = linkPort;
servAddr.sin_addr.S_un.S_addr = localIPInt;
::bind(s, (sockaddr *)&servAddr, sizeof(servAddr));
::listen(s, 1);
sockaddr_in clientAddr;
int lenC = sizeof(clientAddr);
cout<<"TCP server: "<<endl;
SOCKET clientSocket = ::accept(s, (sockaddr *)&clientAddr, &lenC);
cout<<"Recv a connection..."<<endl;
timeval waitTime;
waitTime.tv_sec=2;
waitTime.tv_usec=0;
while(true)
{
fd_set fdSocket;
FD_ZERO(&fdSocket);
FD_SET(clientSocket, &fdSocket);
int nRet = ::select(0, &fdSocket, 0, 0, &waitTime);
if(nRet<0)
{
cout<<"Faild Select()"<<endl;
exit(-1);
}
else if(nRet ==0)
{
cout<<"time out()"<<endl;
continue;
}
else
{
if(FD_ISSET(clientSocket, &fdSocket))
{
char rBuff[100];
int nRec=::recv(clientSocket, rBuff, 100, 0);
cout<<"Recv from client data: "<<nRec<<endl;
if(nRec < 0)
{
cout<<"Not normal close: "<<::GetLastError()<<endl;
break;
}
else if(nRec == 0)
{
cout<<"Normal close"<<endl;
break;
}
else
{
rBuff[nRec]=0;
cout<<"Data : "<<rBuff<<endl;
}
}
}
}
::closesocket(clientSocket);
::closesocket(s);
return 0;
}
客户端代码；
#include "SocketInit.h"
#include "iostream"
using namespace std;
CInitSock sockInit;
int main()
{
SOCKET s = SocketFactory::getTCPSocket();
hostent *thisHost = gethostbyname("");
char *localIP = inet_ntoa (*(struct in_addr *)*thisHost->h_addr_list);
const int localIPInt = inet_addr(localIP);
const unsigned short linkPort = ntohs(4001);//本地监听
sockaddr_in servAddr;
servAddr.sin_family = AF_INET;
servAddr.sin_port = linkPort;
servAddr.sin_addr.S_un.S_addr = localIPInt;
cout<<"Client : "<<endl;
if(::connect(s, (sockaddr *)&servAddr, sizeof(servAddr)) == -1)
{
printf("Faild connect(): %d\n", ::GetLastError());
return 0;
}
char sendStr[100];
while(true)
{
cout<<"Input send data('q' to normal quit): ";
cin.getline(sendStr, 100);
if(sendStr[0]=='q') break;
::send(s, sendStr, strlen(sendStr), 0);
}
::closesocket(s);
return 0;
}
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