對于socket編程一直有一種誤解：socket的阻塞連接下應該調用send/recv來發送和接收數據，而無阻塞連接下應該用WSASend/WSARecv函數來發送和接收數據。其實socket工作模式與調用哪個收發函數沒有任何關系，自己寫段簡單的代碼測試下就知道了。無阻塞模式下，send/recv都是立即返回的。并不會等待發送或接收完成才返回。測試還發現選擇模式下無阻塞連接，調用connect函數會立即返回，隨后調用select，在連接建立時會設置fdWrite。
SOCKET s = ::socket(AF_INET, SOCK_STREAM, IPPROTO_TCP);
if (s == INVALID_SOCKET)
{
return -1;
}
// Set the connection to non-blocking mode
unsigned long ulMode = 1;
if (::ioctlsocket(s, FIONBIO, &ulMode) != 0)
{
s = INVALID_SOCKET;
return -1;
}
char szHost[128] = "www.myhost.com";
int nPort = 8000;
char szBuffer[1024] = "test socket function.\n"
addrinfo aiHints;
addrinfo *aiList = NULL;
memset(&aiHints, 0, sizeof(aiHints));
aiHints.ai_family = AF_INET;
aiHints.ai_socktype = SOCK_STREAM;
aiHints.ai_protocol = IPPROTO_TCP;
if (0 != ::getaddrinfo(szHost, NULL, &aiHints, &aiList))
{
//m_nLastError = WSAGetLastError();
::WSASetLastError(WSAEINVAL);
return -1;
}
fd_set fdRead, fdWrite;
FD_ZERO(&fdRead);
FD_ZERO(&fdWrite);
FD_SET(s, &fdRead);
FD_SET(s, &fdWrite);
struct timeval tv;
tv.tv_sec = 3;
tv.tv_usec = 0;
SOCKADDR_IN hostAddr;
hostAddr = *((SOCKADDR_IN*)aiList->ai_addr);
hostAddr.sin_port = ::htons(nPort);
int retCode = ::connect(s, (SOCKADDR*) &hostAddr, sizeof(hostAddr));
if (retCode == SOCKET_ERROR)
{
int errCode = WSAGetLastError();
if (errCode != WSAEWOULDBLOCK)
{
::closesocket(s);
s = INVALID_SOCKET;
return -1;
}
}
retCode = ::select(0, &fdRead, &fdWrite, NULL, &tv);
if (retCode > 0)
{
if (FD_ISSET(s, &fdRead))
{
printf("error!\n");
}
if (FD_ISSET(s, &fdWrite))
{
//connection has succeeded.
printf("connect success!\n");
FD_SET(s, &fdWrite);
FD_ZERO(&fdRead);
retCode = ::select(0, &fdRead, &fdWrite, NULL, &tv);
if (retCode > 0)
{
if (FD_ISSET(s, &fdRead))
{
printf("error!\n");
}
if (FD_ISSET(s, &fdWrite))
{
retCode = send(s, szBuffer, strlen(szBuffer), 0);
if (retCode > 0)
{
retCode = recv(s, buf, 1023, 0);
if (retCode == SOCKET_ERROR)
{
retCode = WSAGetLastError();
}
else if (retCode > 0)
{
printf("recv %d bytes.\n", retCode);
}
}
}
}
}
}
return 0;很多問題要想深入理解最好的方法就是寫一段短的測試程序驗證一下，既不要想當然也不要道聽途說。