select模型的一个问题

select模型的一个简单程序，读套接口集合中包括监听套接口，但只有第一次connect到来时select返回，后来的connect到来select不返回。当时把代码中FD_SET(clientfd, &read) 代码注释都返回，不知是什么原因。源码如下：

#include <stdio.h>

#include <WinSock2.h>

#include <Windows.h>

#pragma  comment(lib, "ws2_32.lib")

// select(),  fd_set  FD_CLR FD_SET  FD_ISSET  FD_ZERO

int main(int argc, char *argv[])

{
WORD ver = MAKEWORD(2, 2);
WSADATA data;
int nRet = WSAStartup(ver, &data);
if (0 != nRet)
{
return -1;
}

int nError = 0;
SOCKET fd = socket(AF_INET, SOCK_STREAM, IPPROTO_TCP);
if (INVALID_SOCKET == fd)
{
nError = WSAGetLastError();
return -2;
}

sockaddr_in addr;
addr.sin_family = AF_INET;
addr.sin_addr.s_addr = inet_addr("192.168.1.103");
addr.sin_port = htons(10000);
nRet = bind(fd, (sockaddr *)&addr, sizeof(addr));
if (SOCKET_ERROR == nRet)
{
nError = WSAGetLastError();
return -2;
}

nRet = listen(fd, 5);
if (SOCKET_ERROR == nRet)
{
nError = WSAGetLastError();
return -2;
}

fd_set  read;
FD_ZERO(&read);
FD_SET(fd, &read);

fd_set write;
FD_ZERO(&write);

fd_set  except;
FD_ZERO(&except);

while (1)
{
//nRet = select(0, &read, NULL, &except, NULL);
nRet = select(0, &read, &write, &except, NULL);
printf("selet come on...!\n");
if (SOCKET_ERROR == nRet)   //?
{
nError = WSAGetLastError();
return -2;
}
else if (0 == nRet)
{
printf("time out!\n");
continue;
}

for (int j = 0; j < write.fd_count; ++j)
{
if (FD_ISSET(write.fd_array[j], &write))
{
printf("enable write!\n");
}
}

for (int k = 0; k < except.fd_count; ++k)
{
if (FD_ISSET(except.fd_array[k], &except))
{
printf("enable exception!\n");
nError = WSAGetLastError();
}
}

for (int i = 0; i < read.fd_count; ++i)
{
if (FD_ISSET(read.fd_array[i], &read))
{
if (fd == read.fd_array[i])
{
sockaddr_in  addr;
int nSize = sizeof(addr);
SOCKET clientfd = accept(fd, (sockaddr *)&addr, &nSize);
if (SOCKET_ERROR != clientfd)
{
FD_SET(clientfd, &read);
/*FD_SET(clientfd, &except);
FD_SET(clientfd, &write);*/

nRet = getsockname(fd, (sockaddr *)&addr, &nSize);
if (SOCKET_ERROR == nRet)
{
nError = WSAGetLastError();
continue;
}
}
}
else
{
char szRevBuff[4]={0};  //接收缓存区少,待接收的数据量大的情况
int nLen = sizeof(szRevBuff);
nRet = recv(read.fd_array[i], szRevBuff, nLen, 0);
if (SOCKET_ERROR == nRet)
{
nError = WSAGetLastError();
return -5;
}
else if (0 == nRet)   //gracefully closed
{
closesocket(read.fd_array[i]);
}
else
{
printf("recv data: %s!\n", szRevBuff);
}

nRet = send(read.fd_array[i], szRevBuff, nRet, 0);
if (SOCKET_ERROR == nRet)
{
nError = WSAGetLastError();
printf("send data fail: %s!\n", szRevBuff);
}
}
}
}
}

getchar();
return 0;

};