Windows socket之最简单的socket程序

原文:Windows socket之最简单的socket程序

最简单的服务器的socket程序流程如下(面向连接的TCP连接 ):

1. WSAStartup(); 初始化网络库的使用。

2. socket(); 获得一个socket。

3. bind(); 把获得的socket绑定到一个ip 和端口。既然作为服务器, ip通常为本地IP127.0.0.1。

4. listen(); 监听已经绑定了指定端口的socket。

5. accept(); 接受一个来自客户端的连接。

accept()返回一个新的socket,该socket代表着本地服务器与某一个连接过来的客户端的链接。以该socket为参数，可以调用send函数往客户端发送数据，也可以调用recv函数接受客户端发送过来的函数。

最后服务器程序结束的时候调用closesocket()关闭socket, WSACleanup()终止网络库的使用，清理资源。

最简单的客户端的socket程序流程如下(同样是面向连接的TCP连接):

1. WSAStartup();初始化网络库的使用。

2. socket(); 获得一个socket。

3. connect(); 连接到一个 服务器。

连接成功后就可以收发数据了。收发完毕后调用closesocket()关闭socket,最后程序结束前调用 WSACleanup()清理资源。

下面直接上代码

需包含以下头文件和定义

#include <stdlib.h>
#include <stdio.h>
#include <WinSock2.h>
#pragma comment(lib,"ws2_32.lib")

#define SERVE_ADDRESS "127.0.0.1"
#define SERVE_PORT    7001

	// ----------------------------       WSAStartup()         ----------------------------//WSADATA wsd;int resStartup = WSAStartup(MAKEWORD(2,2),&wsd);if(0 != resStartup){printf("failed to WSAStartup!\n");goto Main_End;}//------------------------------------------------------------------------------//// ----------------------------         socket()         ----------------------------//SOCKET serverSocket = socket(AF_INET,SOCK_STREAM,IPPROTO_TCP);if(INVALID_SOCKET == serverSocket){printf("failed to invoke socket, the socket returned is invalid!\n");goto Main_End;}// ------------------------------------------------------------------------------------////----------------------------           bind()          ----------------------------//// 初始化 struct sockaddr 结构体， SOCKADDR_IN就是 struct sockaddr的宏定义SOCKADDR_IN localAddr;localAddr.sin_family = AF_INET;localAddr.sin_addr.S_un.S_addr = inet_addr(SERVE_ADDRESS);	localAddr.sin_port = htons(SERVE_PORT);	memset(localAddr.sin_zero,0x0,sizeof(localAddr.sin_zero));// int resBind = bind(serverSocket,(sockaddr*)&localAddr,sizeof(SOCKADDR_IN));if(0 != resBind){printf("failed to bind ! \n");goto Main_End;}//------------------------------------------------------------------------------------////----------------------------          listen()         ----------------------------//int resListen = listen(serverSocket,5);if(0 != resListen){printf("failed to listen! \n");goto Main_End;}printf("the server is listening now!\n");//------------------------------------------------------------------------------------////----------------------------        accept()         ----------------------------//SOCKADDR_IN clientAddr;int addrLen = sizeof(clientAddr);SOCKET acceptedSocket = accept(serverSocket,(sockaddr*)&clientAddr,&addrLen);if(INVALID_SOCKET == acceptedSocket){printf("accept error!\n");goto Main_End;}printf("a client has connected to the server!\n");//------------------------------------------------------------------------------------//char recvBuffer[256];char sendBuffer[256];strcpy(sendBuffer,"server:Welcome to connect !");int sendBufLen = strlen(sendBuffer);int resSend = send(acceptedSocket,sendBuffer,sendBufLen,0);while(true){if(resSend != sendBufLen)	//发送的长度与需要发送的长度不等{printf("send data error!!\n");break;}int recvLen = recv(acceptedSocket,recvBuffer,sizeof(recvBuffer),0);if(0 == recvLen){printf("a client close the socket!\n");break;}else if(recvLen < 0){printf("an error has happen when receiving\n");break;}recvBuffer[recvLen] = '\0';printf("client:%s\n",recvBuffer);//在客户发过来的数据前面加上server:再发回给客户端strcpy(sendBuffer,"server:");strcat(sendBuffer,recvBuffer);sendBufLen = strlen(sendBuffer);resSend = send(acceptedSocket,sendBuffer,sendBufLen,0);}closesocket(acceptedSocket);closesocket(serverSocket);Main_End:WSACleanup();system("pause");return 0;

客户端代码：

	//----------------------------       WSAStartup()        ----------------------------//WSADATA wsd;int resStartup = WSAStartup(MAKEWORD(2,2),&wsd);if(0 != resStartup){printf("failed to WSAStartup!\n");goto Main_End;}//------------------------------------------------------------------------------------////----------------------------       socket()           ----------------------------//SOCKET connSocket = socket(AF_INET,SOCK_STREAM,IPPROTO_TCP);if(INVALID_SOCKET == connSocket){printf("the socket returned is invalid!\n");goto Main_End;}//------------------------------------------------------------------------------------////----------------------------       connect()         ----------------------------////初始化struct sockaddr 结构体 SOCKADDR_IN serverAddr;serverAddr.sin_family = AF_INET;serverAddr.sin_addr.S_un.S_addr = inet_addr(SERVE_ADDRESS);serverAddr.sin_port = htons(SERVE_PORT);memset(serverAddr.sin_zero,0x0,sizeof(serverAddr.sin_zero));//connectint resConn = connect(connSocket,(sockaddr*)&serverAddr,sizeof(serverAddr));if(0 != resConn){printf("failed to connect to server!!\n");goto Main_End;}//------------------------------------------------------------------------------------//char sendBuffer[256];char recvBuffer[256];while(true){int recvLen = recv(connSocket,recvBuffer,256,0);if(recvLen < 0){printf("receive error!!\n");break;}else if(0 == recvLen){printf("the server close the socket!\n");}recvBuffer[recvLen] = '\0';printf("the data recv:%s\n\n\n",recvBuffer);printf("please input what you want to send:\n");gets(sendBuffer);if(0 == strcmp(sendBuffer,"exit")){break;}int sendDataLen = strlen(sendBuffer);int nDataSent = send(connSocket,sendBuffer,sendDataLen,0);if(nDataSent != sendDataLen){printf("failed to send data!!\n");break;}}closesocket(connSocket);printf("the connection is closed!\n");Main_End:WSACleanup();system("pause");return 0;

客户端连接到服务端后，每次给服务端发送一段内容，服务器在内容前面加上server:再发送给客户端。

当客户端发送的内容是exit时，客户端程序跳出循环，关闭socket断开连接。服务端发现客户端断开连接后也关闭套接字结束程序。

当然上面程序只为了演示最简单的网络编程。有若干漏洞。

1. 服务器只能接受一个客户端连接。当然加一个循环语句进去可以重复地接受客户端的连接，但是仍然是每次只处理一个客户端连接。

2.accept, connect,send,recv函数默认均是阻塞函数。当没有客户连接到服务端时，服务端阻塞在accept函数，无法退出程序。当服务器在接受客户端的数据时，如果客户端不发送数据，也不断开连接，那么服务端阻塞在recv函数，无法退出程序。

改进该程序，使得服务端随时都可以停止服务退出程序，无论有多少个用户已经在连接。

为了多个客户端可以同时连接，最容易理解的便是利用多线程。每一个连接的客户端都用一个线程去处理它的通信。

至于为了随时可以退出服务端，不能再调用永久阻塞的函数了。利用select函数，可以阻塞指定的时间，阻塞期间不占CPU。

int select( __in int nfds, __in_out fd_set*readfds, __in_out fd_set*writefds, __in_out fd_set*exceptfds, __in const struct timeval*timeout);

nfds

用于兼容Berkeley sockets.不用理会，随便给个0值就OK。

readfds

用于检查是否存在可读socket的的一个socket集合。可为空。

writefds

用于检查是否存在可写socket的一个socket集合。可为空。

exceptfds

用于检查是否存在有错误的socket的一个 socket集合，可为空。

timeout

TIMEVAL结构体，用于指定该函数阻塞多长时间。

在 调用select时，当readfds不为空时，当readfds中任何一个socket就绪可读时，或者当writefds不为空且writefds中任何一个socket准备就绪可写，或者当exceptfds不为空且任何一个socket发生socket错误时，select就立即返回。否则，直到timeout指定的时间过去以后才返回。

返回值，返回准备就绪的socket的个数。如果为0，说明该函数超时了，如果大于0，说明至少有一个socket就绪。如果小于0，说明发生错误了。

fd_set 是一种集合类型。

typedef struct fd_set {
        u_int fd_count;               /* how many are SET? */
        SOCKET  fd_array[FD_SETSIZE];   /* an array of SOCKETs */
} fd_set;

记录着一个socket数组，以及里面的socket个数。

struct timeval是一个表示等待时间的结构体。

struct timeval {
        long    tv_sec;         /* seconds */
        long    tv_usec;        /* and microseconds */
};

tv_sec表示有多少秒，tv_usec表示有多少毫秒。

对于fd_set类型，用到几个宏定义函数。

FD_ZERO(fd_set*), 清空fd_set集合

FD_SET(SOCKET,fd_set*),把socket加入fd_set集合。

FD_ISSET(SOCKET,fd_set*),判断socket是否在集合fd_set中，并且socket准备就绪。

FD_CLR(SOCKET,fd_set*),如果fd_set存在该SOCKET，则移除它。

下面是改进后的服务端代码

typedef struct _ThreadInfo
{HANDLE hThread;bool bRunning;SOCKET sock;
}ThreadInfo;typedef struct _AcceptThreadParam
{bool bRunning;SOCKET listeningSocket;
}AcceptThreadParam;std::list<ThreadInfo*> g_threadInfoList;
CRITICAL_SECTION g_csForList;DWORD WINAPI ListeningThread(LPVOID lpParameter);
DWORD WINAPI CommunicationThread(LPVOID lpParameter);int _tmain(int argc, _TCHAR* argv[])
{_CrtSetDbgFlag(_CRTDBG_ALLOC_MEM_DF | _CRTDBG_LEAK_CHECK_DF);// ----------------------------       WSAStartup()         ----------------------------//WSADATA wsd;int resStartup = WSAStartup(MAKEWORD(2,2),&wsd);if(0 != resStartup){printf("failed to WSAStartup!\n");return -1;}//------------------------------------------------------------------------------//InitializeCriticalSection(&g_csForList);// ----------------------------         socket()         ----------------------------//SOCKET serverSocket = socket(AF_INET,SOCK_STREAM,IPPROTO_TCP);if(INVALID_SOCKET == serverSocket){printf("failed to invoke socket, the socket returned is invalid!\n");goto Main_End;}// ------------------------------------------------------------------------------------////----------------------------           bind()          ----------------------------//// 初始化 struct sockaddr 结构体， SOCKADDR_IN就是 struct sockaddr的宏定义SOCKADDR_IN localAddr;localAddr.sin_family = AF_INET;localAddr.sin_addr.S_un.S_addr = inet_addr(SERVE_ADDRESS);	localAddr.sin_port = htons(SERVE_PORT);	memset(localAddr.sin_zero,0x0,sizeof(localAddr.sin_zero));// int resBind = bind(serverSocket,(sockaddr*)&localAddr,sizeof(SOCKADDR_IN));if(0 != resBind){printf("failed to bind ! \n");goto Main_End;}//------------------------------------------------------------------------------------////----------------------------          listen()         ----------------------------//int resListen = listen(serverSocket,5);if(0 != resListen){printf("failed to listen! \n");goto Main_End;}//------------------------------------------------------------------------------------//AcceptThreadParam threadParam;threadParam.bRunning = true;threadParam.listeningSocket = serverSocket;HANDLE hListeningThread = CreateThread(0,0,ListeningThread,&threadParam,0,0);if(0 == hListeningThread){printf("failed to create the listening thread!\n");goto Main_End;}else{printf("the server is listening now!pass any key to close the server!\n");}while(true){char ch = getchar();threadParam.bRunning = false;DWORD resWait = WaitForSingleObject(hListeningThread,3000);if(WAIT_TIMEOUT == resWait){printf("failed to wait for the listening thread exiting!\n");}else{printf("the listening thread has exited!\n");}break;}Main_End:if(INVALID_SOCKET != serverSocket){closesocket(serverSocket);serverSocket = INVALID_SOCKET;}WSACleanup();DeleteCriticalSection(&g_csForList);system("pause");return 0;
}DWORD WINAPI ListeningThread(LPVOID lpParameter)
{AcceptThreadParam* pAcceptThreadParam = (AcceptThreadParam*)lpParameter;SOCKET serverSocket = pAcceptThreadParam->listeningSocket;while(pAcceptThreadParam->bRunning){//----------------------------        accept()         ----------------------------//fd_set fdAccept;FD_ZERO(&fdAccept);FD_SET(serverSocket,&fdAccept);TIMEVAL acceptTimeVal;acceptTimeVal.tv_sec = 1;acceptTimeVal.tv_usec = 0;int selRes = select(0,&fdAccept,0,0,&acceptTimeVal);if(selRes > 0){SOCKADDR_IN clientAddr;int addrLen = sizeof(clientAddr);SOCKET acceptedSocket = accept(serverSocket,(sockaddr*)&clientAddr,&addrLen);if(INVALID_SOCKET == acceptedSocket){printf("accept error!\n");break;}printf("a client has connected to the server!\n");ThreadInfo* pTI = new ThreadInfo;pTI->bRunning = true;pTI->sock = acceptedSocket;pTI->hThread = CreateThread(0,0,CommunicationThread,(LPVOID)pTI,0,0);if(0 == pTI->hThread){printf("failed to create a thread!\n");delete pTI;pTI = 0;}else{EnterCriticalSection(&g_csForList);g_threadInfoList.push_back(pTI);LeaveCriticalSection(&g_csForList);}}else if(selRes < 0){printf("an error has occured when listening !\n");break;}}std::list<ThreadInfo*> tempList;EnterCriticalSection(&g_csForList);std::list<ThreadInfo*>::iterator listIter;for(listIter = g_threadInfoList.begin(); listIter != g_threadInfoList.end(); listIter++){(*listIter)->bRunning = false;tempList.push_back(*listIter);}g_threadInfoList.clear();LeaveCriticalSection(&g_csForList);int nSuccessfullyExit = 0;for(listIter = tempList.begin(); listIter != tempList.end(); listIter++){DWORD resWait = WaitForSingleObject((*listIter)->hThread,2000);if(WAIT_TIMEOUT == resWait){printf("failed to wait for a communication thread exiting!\n");}else{nSuccessfullyExit++;}delete (*listIter);}printf("succeed waiting for %d thread exiting!\n",nSuccessfullyExit);tempList.clear();printf("listening thread is exiting!\n");return 0;
}DWORD WINAPI CommunicationThread(LPVOID lpParameter)
{ThreadInfo* pThreadInfo = (ThreadInfo*)lpParameter;SOCKET clientSocket = pThreadInfo->sock;fd_set fdRead,fdWrite;FD_ZERO(&fdRead);FD_ZERO(&fdWrite);FD_SET(clientSocket,&fdRead);FD_SET(clientSocket,&fdWrite);TIMEVAL sendTimeVal;sendTimeVal.tv_sec = 0;sendTimeVal.tv_usec = 500;int selRes = select(0,0,&fdWrite,0,&sendTimeVal);if(selRes <= 0){goto ThreadOver;}char recvBuffer[256];char sendBuffer[256];strcpy(sendBuffer,"server:Welcome to connect !");int sendBufLen = strlen(sendBuffer);int resSend = send(clientSocket,sendBuffer,sendBufLen,0);if(resSend != sendBufLen){printf("there are %d bytes to send, but it just succeeded sending %d bytes!\n",sendBufLen,resSend);goto ThreadOver;}while(pThreadInfo->bRunning){	FD_ZERO(&fdRead);FD_SET(pThreadInfo->sock,&fdRead);TIMEVAL recvTimeVal;recvTimeVal.tv_sec = 0;recvTimeVal.tv_usec = 500;int recvSelRes = select(0,&fdRead,0,0,&recvTimeVal);if(recvSelRes < 0){printf("socket error when receiving!\n");break;}else if(recvSelRes > 0){int recvLen = recv(clientSocket,recvBuffer,sizeof(recvBuffer),0);if(0 == recvLen){printf("a client close the socket!\n");break;}else if(recvLen < 0){printf("an error has happen when recving\n");break;}else{recvBuffer[recvLen] = '\0';printf("a client:%s\n",recvBuffer);strcpy(sendBuffer,"server:");strcat(sendBuffer,recvBuffer);sendBufLen = strlen(sendBuffer);FD_ZERO(&fdWrite);FD_SET(pThreadInfo->sock,&fdWrite);sendTimeVal.tv_sec = 0;sendTimeVal.tv_usec = 500;int sendSelRes = select(0,0,&fdWrite,0,&sendTimeVal);if(sendSelRes > 0){int bytesSent = send(clientSocket,sendBuffer,sendBufLen,0);if(bytesSent != sendBufLen){printf("there are %d bytes to be sent,but only %d bytes are sent!\n",sendBufLen,bytesSent);break;}}else{printf("failed to send in 500 ms!\n");break;}}}}ThreadOver:closesocket(pThreadInfo->sock);bool bMainThreadWaiting = true;EnterCriticalSection(&g_csForList);std::list<ThreadInfo*>::iterator listIter;for(listIter = g_threadInfoList.begin(); listIter != g_threadInfoList.end(); listIter++){if(pThreadInfo == (*listIter)){bMainThreadWaiting = false;g_threadInfoList.erase(listIter);break;}}LeaveCriticalSection(&g_csForList);if(false == bMainThreadWaiting){CloseHandle(pThreadInfo->hThread);delete pThreadInfo;pThreadInfo = 0;}return 0;
}

前面的代码与之前的一样，改变的地方在于accept的地方。对于一个监听的socket,如果该socket可读，说明有用户连接过来了。

全局维护了一个纪录创建的线程的信息的链表，每创建一个线程都有一个标识该线程是否应该继续循环执行的bool变量。当bRunning变为false的时候，线程函数跳出循环，返回。

当需要停止服务端运行时，服务端只需要按任何一个键和回车，就会通知线程退出，并且调用WaitForSingleObject(),来确认线程已退出。还有利用了 EnterCriticalSection()和LeaveCriticalSection()临界区函数来保证只有一个线程在操作全局的链表。

使用多线程要消耗一定的资源。对于fd_set，默认最多可以容纳64个socket.所以可以用1个线程去处理64个客户端的连接。而不必每个客户端都创建一个线程。

代码如下：

typedef struct _AcceptThreadParam
{bool bRunning;SOCKET listeningSocket;
}AcceptThreadParam;#define SOCKET_ARRAY_SIZE 64SOCKET g_socketArray[SOCKET_ARRAY_SIZE];
int g_socketCount = 0;
CRITICAL_SECTION g_csForSocketArray;DWORD WINAPI ListeningThread(LPVOID lpParameter);
DWORD WINAPI CommunicationThread(LPVOID lpParameter);int _tmain(int argc, _TCHAR* argv[])
{_CrtSetDbgFlag(_CRTDBG_ALLOC_MEM_DF | _CRTDBG_LEAK_CHECK_DF);// ----------------------------       WSAStartup()         ----------------------------//WSADATA wsd;int resStartup = WSAStartup(MAKEWORD(2,2),&wsd);if(0 != resStartup){printf("failed to WSAStartup!\n");return -1;}//------------------------------------------------------------------------------//InitializeCriticalSection(&g_csForSocketArray);g_socketCount = 0;// ----------------------------         socket()         ----------------------------//SOCKET serverSocket = socket(AF_INET,SOCK_STREAM,IPPROTO_TCP);if(INVALID_SOCKET == serverSocket){printf("failed to invoke socket, the socket returned is invalid!\n");goto Main_End;}// ------------------------------------------------------------------------------------////----------------------------           bind()          ----------------------------//// 初始化 struct sockaddr 结构体， SOCKADDR_IN就是 struct sockaddr的宏定义SOCKADDR_IN localAddr;localAddr.sin_family = AF_INET;localAddr.sin_addr.S_un.S_addr = inet_addr(SERVE_ADDRESS);	localAddr.sin_port = htons(SERVE_PORT);	memset(localAddr.sin_zero,0x0,sizeof(localAddr.sin_zero));// int resBind = bind(serverSocket,(sockaddr*)&localAddr,sizeof(SOCKADDR_IN));if(0 != resBind){printf("failed to bind ! \n");goto Main_End;}//------------------------------------------------------------------------------------////----------------------------          listen()         ----------------------------//int resListen = listen(serverSocket,5);if(0 != resListen){printf("failed to listen! \n");goto Main_End;}//------------------------------------------------------------------------------------//AcceptThreadParam threadParam;threadParam.bRunning = true;threadParam.listeningSocket = serverSocket;bool bCommunicationThreadRunning = true;HANDLE hListeningThread = CreateThread(0,0,ListeningThread,&threadParam,0,0);HANDLE hCommunicationThread = CreateThread(0,0,CommunicationThread,&bCommunicationThreadRunning,0,0);if(0 == hListeningThread || 0 == hCommunicationThread){printf("failed to create a thread!\n");if(0 != hListeningThread){threadParam.bRunning = false;WaitForSingleObject(hListeningThread,2000);CloseHandle(hListeningThread);}if(0 != hCommunicationThread){bCommunicationThreadRunning = false;WaitForSingleObject(hCommunicationThread,2000);CloseHandle(hCommunicationThread);}goto Main_End;}else{printf("the server is listening now!pass any key to close the server!\n");}while(true){char ch = getchar();threadParam.bRunning = false;bCommunicationThreadRunning = false;DWORD resWait = WaitForSingleObject(hListeningThread,3000);if(WAIT_TIMEOUT == resWait){printf("failed to wait for the listening thread exiting!\n");}else{printf("the listening thread has exited!\n");}CloseHandle(hListeningThread);resWait = WaitForSingleObject(hCommunicationThread,3000);if(WAIT_TIMEOUT == resWait){printf("failed to wait for the communication thread exiting!\n");}else{printf("the communication thread has exited!\n");}CloseHandle(hCommunicationThread);break;}Main_End:if(INVALID_SOCKET != serverSocket){closesocket(serverSocket);serverSocket = INVALID_SOCKET;}WSACleanup();DeleteCriticalSection(&g_csForSocketArray);system("pause");return 0;
}DWORD WINAPI ListeningThread(LPVOID lpParameter)
{AcceptThreadParam* pAcceptThreadParam = (AcceptThreadParam*)lpParameter;SOCKET serverSocket = pAcceptThreadParam->listeningSocket;while(pAcceptThreadParam->bRunning){//----------------------------        accept()         ----------------------------//fd_set fdAccept;FD_ZERO(&fdAccept);FD_SET(serverSocket,&fdAccept);TIMEVAL acceptTimeVal;acceptTimeVal.tv_sec = 1;acceptTimeVal.tv_usec = 0;int selRes = select(0,&fdAccept,0,0,&acceptTimeVal);if(selRes > 0){SOCKADDR_IN clientAddr;int addrLen = sizeof(clientAddr);SOCKET acceptedSocket = accept(serverSocket,(sockaddr*)&clientAddr,&addrLen);if(INVALID_SOCKET == acceptedSocket){printf("accept error!\n");break;}printf("a client has connected to the server!\n");fd_set fdWrite;FD_ZERO(&fdWrite);FD_SET(acceptedSocket,&fdWrite);TIMEVAL writeTimeVal;writeTimeVal.tv_sec = 0;writeTimeVal.tv_usec = 500;int writeSelRes = select(0,0,&fdWrite,0,&writeTimeVal);if(writeSelRes > 0){int sendBufferLen = strlen("server:Welcome to connect!");int bytesSent = send(acceptedSocket,"server:Welcome to connect!",sendBufferLen,0);if(bytesSent == sendBufferLen){EnterCriticalSection(&g_csForSocketArray);if(g_socketCount < 64){g_socketArray[g_socketCount] = acceptedSocket;g_socketCount++;}else{printf("the server has accepted more than 64 clients!\n");closesocket(acceptedSocket);}LeaveCriticalSection(&g_csForSocketArray);}else{printf("send error, there are %d bytes to be sent, but only %d bytes are sent!\n",sendBufferLen,bytesSent);closesocket(acceptedSocket);}}else{printf("select error of can not wait for sending data when select!\n");closesocket(acceptedSocket);}}else if(selRes < 0){printf("an error has occured when listening !\n");break;}}printf("listening thread is exiting!\n");return 0;
}DWORD WINAPI CommunicationThread(LPVOID lpParameter)
{bool* pBRunning = (bool*)lpParameter;char recvBuffer[256];char tempBuffer[256];while(true == *pBRunning){int currentSocketCount = 0;EnterCriticalSection(&g_csForSocketArray);if(0 == g_socketCount){LeaveCriticalSection(&g_csForSocketArray);Sleep(200);continue;}currentSocketCount = g_socketCount;LeaveCriticalSection(&g_csForSocketArray);fd_set fdRead;FD_ZERO(&fdRead);for(int i = 0; i < currentSocketCount; i++){FD_SET(g_socketArray[i],&fdRead);}TIMEVAL readTimeVal;readTimeVal.tv_sec = 1;readTimeVal.tv_usec = 0;int selRes = select(0,&fdRead,0,0,&readTimeVal);if(selRes > 0){for(int i = 0; i < currentSocketCount; i++){if(FD_ISSET(g_socketArray[i],&fdRead) != 0){int bytesRecv = recv(g_socketArray[i],recvBuffer,sizeof(recvBuffer),0);if(bytesRecv > 0){recvBuffer[bytesRecv] = '\0';printf("the %d client: %s\n",i + 1,recvBuffer);sprintf(tempBuffer,"the server:%s",recvBuffer);fd_set fdWrite;FD_ZERO(&fdWrite);FD_SET(g_socketArray[i],&fdWrite);TIMEVAL writeTimeVal;writeTimeVal.tv_sec = 0;writeTimeVal.tv_usec = 500;int writeSelRes = select(g_socketArray[i],0,&fdWrite,0,&writeTimeVal);if(writeSelRes > 0){int sendBufLen = strlen(tempBuffer);int bytesSent = send(g_socketArray[i],tempBuffer,sendBufLen,0);if(bytesSent == sendBufLen){break;}else{printf("there are %d bytes to be sent,but only %d bytes are sent!\n",sendBufLen,bytesSent);}}else{printf("select error!\n");}}else if(0 == bytesRecv){printf("the %d client has closed the socket!\n",i + 1);}else{printf("recv error!\n");}closesocket(g_socketArray[i]);EnterCriticalSection(&g_csForSocketArray);g_socketArray[i] = g_socketArray[g_socketCount - 1];g_socketCount--;LeaveCriticalSection(&g_csForSocketArray);}}}else if(selRes < 0){printf("select error in communication thread!\n");}}EnterCriticalSection(&g_csForSocketArray);for(int i = 0; i < g_socketCount; i++){closesocket(g_socketArray[i]);}LeaveCriticalSection(&g_csForSocketArray);printf("the communication thread is exiting!\n");return 0;
}

完成的功能一样。只需要一个线程就可以处理多个客户端了。

还可以用异步IO来实现该服务器，以下是用完成端口来实现同样功能的服务器。

typedef struct _RepeatAcceptingThreadParam
{SOCKET listeningSocket;bool* pBRunning;
}RepeatAcceptingThreadParam;typedef struct _CompletionPortWorkerThreadParam
{HANDLE hCompletionPort;bool* pBRunning;
}CompletionPortWorkerThreadParam;#define MESSAGE_BUF_SIZE 1024enum OPERATION_TYPE
{OPERATION_SEND,OPERATION_RECV
};typedef struct
{SOCKET sock;WSAOVERLAPPED overlap;WSABUF wsaBuf;char message[1024];DWORD bytesRecv;DWORD flags;OPERATION_TYPE operationType;
}PER_IO_OPERATION_DATA;//global vector, which saves the information of the client sockets connected to the server
std::vector<PER_IO_OPERATION_DATA*> g_perIoDataPointerVec;//accept sockets connected to the server's listening socket in a recycle - while
DWORD WINAPI RepeatAcceptingThread(LPVOID lpParameter);	//the worker thread that deal with the communications between the server and the clients.
DWORD WINAPI CompletionPortWorkerThread(LPVOID lpParameter);int _tmain(int argc,_TCHAR* argv[])
{_CrtSetDbgFlag(_CRTDBG_ALLOC_MEM_DF | _CRTDBG_LEAK_CHECK_DF);// ----------------------------       WSAStartup()         ----------------------------//WSADATA wsd;int resStartup = WSAStartup(MAKEWORD(2,2),&wsd);if(0 != resStartup){printf("failed to WSAStartup!\n");return -1;}//------------------------------------------------------------------------------//// ----------------------------         socket()         ----------------------------//SOCKET serverSocket = socket(AF_INET,SOCK_STREAM,IPPROTO_TCP);if(INVALID_SOCKET == serverSocket){printf("failed to invoke socket, the socket returned is invalid!\n");return -1;}// ------------------------------------------------------------------------------------////----------------------------           bind()          ----------------------------//// 初始化 struct sockaddr 结构体， SOCKADDR_IN就是 struct sockaddr的宏定义SOCKADDR_IN localAddr;localAddr.sin_family = AF_INET;localAddr.sin_addr.S_un.S_addr = inet_addr(SERVE_ADDRESS);	localAddr.sin_port = htons(SERVE_PORT);	memset(localAddr.sin_zero,0x0,sizeof(localAddr.sin_zero));// int resBind = bind(serverSocket,(sockaddr*)&localAddr,sizeof(SOCKADDR_IN));if(0 != resBind){printf("failed to bind ! \n");closesocket(serverSocket);return -1;}//------------------------------------------------------------------------------------////----------------------------          listen()         ----------------------------//int resListen = listen(serverSocket,5);if(0 != resListen){printf("failed to listen! \n");closesocket(serverSocket);return -1;}//------------------------------------------------------------------------------------//bool bRepeatAcceptingThreadRunning = true;	// a bool variable that take control of terminating the RepeatAcceptingThread.//init the parameter for the RepeatAcceptingThread.RepeatAcceptingThreadParam rtp;rtp.listeningSocket = serverSocket;rtp.pBRunning = &bRepeatAcceptingThreadRunning;HANDLE hRepeatAcceptingThread = CreateThread(0,0,RepeatAcceptingThread,&rtp,0,0);if(0 == hRepeatAcceptingThread){printf("failed to create the repeat-accepting thread!\n");closesocket(serverSocket);return -1;}printf("the repeat-accepting thread has run!\n");while(true){// pass any key char ch = getchar();bRepeatAcceptingThreadRunning = false;//to notify the RepeatAcceptingThread to exit safely DWORD waitRes = WaitForSingleObject(hRepeatAcceptingThread,3000);if(WAIT_TIMEOUT == waitRes){printf("failed to wait for the repeatAcceptingThread exiting!\n");}else{printf("the repeat accepting thread has exited!\n");}CloseHandle(hRepeatAcceptingThread);break;}system("pause");return 0;
}DWORD WINAPI RepeatAcceptingThread(LPVOID lpParameter)
{//get the parameters passed by the creator of the thread.RepeatAcceptingThreadParam* pParam = (RepeatAcceptingThreadParam*)lpParameter;SOCKET listeningSocket = pParam->listeningSocket;bool* pStillRun = pParam->pBRunning;// create a completion portHANDLE hCompletionPort = CreateIoCompletionPort(INVALID_HANDLE_VALUE,0,0,0);if(0 == hCompletionPort){printf("failed to CreateIoCompletionPort!\n");return -1;}// a bool variable for notifying the worker threads of exiting.bool bWorkThreadRunning = true;// a vector of HANDLEs,which will be used for synchronization of waiting the worker threads to exit.std::vector<HANDLE> threadHandlesVec;SYSTEM_INFO systemInfo;GetSystemInfo(&systemInfo);//the parameter to be passed to the worker thread.CompletionPortWorkerThreadParam cpwtp;cpwtp.pBRunning = &bWorkThreadRunning;cpwtp.hCompletionPort = hCompletionPort;for(int i = 0; i < systemInfo.dwNumberOfProcessors; i++){HANDLE hThread = CreateThread(0,0,CompletionPortWorkerThread,&cpwtp,0,0);if(0 == hThread)	{printf("failed to create a completion port worker thread!\n");bWorkThreadRunning = false;// terminate all threads created safely.std::vector<HANDLE>::iterator vecIter;for(vecIter = threadHandlesVec.begin(); vecIter != threadHandlesVec.end(); vecIter++){DWORD waitRes = WaitForSingleObject(*vecIter,2000);if(WAIT_TIMEOUT == waitRes){printf("failed the wait for the completion port worker thread!\n");}CloseHandle(*vecIter);}threadHandlesVec.clear();CloseHandle(hCompletionPort);return -1;}else{threadHandlesVec.push_back(hThread);	//add the handle to the vector}}printf("succeed creating completion port worker threads!\n");while(true == *pStillRun){fd_set fdAccept;FD_ZERO(&fdAccept);FD_SET(listeningSocket,&fdAccept);TIMEVAL acceptTimeVal;acceptTimeVal.tv_sec = 1;acceptTimeVal.tv_usec = 0;int selRes = select(0,&fdAccept,0,0,&acceptTimeVal);if(selRes > 0)	// a client connected{SOCKADDR_IN clientAddr;int addrLen = sizeof(clientAddr);SOCKET acceptedSocket = WSAAccept(listeningSocket,(struct sockaddr*)&clientAddr,&addrLen,0,0);if(0 == acceptedSocket){printf("failed to accept a connection!\n");}else{printf("a clent %s:%d has connected!\n",inet_ntoa(clientAddr.sin_addr),ntohs(clientAddr.sin_port));PER_IO_OPERATION_DATA* perIoData = new PER_IO_OPERATION_DATA;if(0 == perIoData){closesocket(acceptedSocket);printf("failed to new a struct! there is not enough memory!\n\n");}else{//associate the newly connected client socket with the completion port.if(0 == CreateIoCompletionPort((HANDLE)acceptedSocket,hCompletionPort,(ULONG_PTR)perIoData,0)){printf("failed to associate the newly connected client socket with the completion port!\n");closesocket(acceptedSocket);delete perIoData;perIoData = 0;}else{//associated successfully, Set the information of the client socket in A PER_IO_OPERATION_DATA struct.//when a IO operation is completed, we can get notified with the struct to be one of the parameters.perIoData->sock = acceptedSocket;perIoData->operationType = OPERATION_SEND;perIoData->wsaBuf.buf = perIoData->message;perIoData->overlap.hEvent = INVALID_HANDLE_VALUE;strcpy(perIoData->message,"Welcome to connect to the server!");perIoData->wsaBuf.len = strlen(perIoData->message);int sendRes = WSASend(acceptedSocket,&(perIoData->wsaBuf),1,&(perIoData->bytesRecv),0,0,0);if(0 == sendRes)	//finished immediately{// asynchronously invoke a receive operation. When the reception finished,we can get its information by// invoking GetQueuedCompletionStatus()perIoData->wsaBuf.buf = perIoData->message;perIoData->wsaBuf.len = MESSAGE_BUF_SIZE;perIoData->flags = 0;perIoData->operationType = OPERATION_RECV;ZeroMemory(&perIoData->overlap,sizeof(perIoData->overlap));int recvRes = WSARecv(acceptedSocket,&perIoData->wsaBuf,1,&perIoData->bytesRecv,&perIoData->flags,&perIoData->overlap,0);if(0 == recvRes)	//the receiving operation finished immediately , the information of the operation has been queued.{g_perIoDataPointerVec.push_back(perIoData);}else if(SOCKET_ERROR == recvRes && WSA_IO_PENDING == WSAGetLastError())	//the receiving operation will finish later{g_perIoDataPointerVec.push_back(perIoData);}else{printf("failed to WSARecv!\n");closesocket(acceptedSocket);delete perIoData;perIoData = 0;}}else if(SOCKET_ERROR == sendRes && WSA_IO_PENDING == WSAGetLastError())		//the sending operation will finish later{g_perIoDataPointerVec.push_back(perIoData);}else{//int lastErr = WSAGetLastError();printf("send data error!\n");closesocket(acceptedSocket);delete perIoData;perIoData = 0;}}}}}else if(selRes < 0){printf("select error!\n");}}bWorkThreadRunning = false;	//notifies the worker threads of exiting// terminate all threads created safely.std::vector<HANDLE>::iterator vecIter;for(vecIter = threadHandlesVec.begin(); vecIter != threadHandlesVec.end(); vecIter++){DWORD waitRes = WaitForSingleObject(*vecIter,2000);if(WAIT_TIMEOUT == waitRes){printf("failed the wait for the completion port worker thread!\n");}CloseHandle(*vecIter);}threadHandlesVec.clear();CloseHandle(hCompletionPort);//delete the structs of PER_IO_OPERATION_DATA newed for clients connected.std::vector<PER_IO_OPERATION_DATA*>::iterator pIoDataPointerIter;for(pIoDataPointerIter = g_perIoDataPointerVec.begin(); pIoDataPointerIter != g_perIoDataPointerVec.end(); pIoDataPointerIter++){closesocket((*pIoDataPointerIter)->sock);delete (*pIoDataPointerIter);*pIoDataPointerIter = 0;}g_perIoDataPointerVec.clear();printf(" the repeat accepting thread is exiting!\n");return 0;
}bool ReleaseIOOperationData(PER_IO_OPERATION_DATA* & pDataToBeDeleted)
{bool retVal = false;std::vector<PER_IO_OPERATION_DATA*>::iterator vecIter;for(vecIter = g_perIoDataPointerVec.begin(); vecIter != g_perIoDataPointerVec.end(); vecIter++){if(pDataToBeDeleted == (*vecIter)){g_perIoDataPointerVec.erase(vecIter);closesocket(pDataToBeDeleted->sock);delete pDataToBeDeleted;pDataToBeDeleted = 0;retVal = true;break;}}return retVal;
}DWORD WINAPI CompletionPortWorkerThread(LPVOID lpParameter)
{CompletionPortWorkerThreadParam* pParam = (CompletionPortWorkerThreadParam*)lpParameter;bool* pStillRun = pParam->pBRunning;HANDLE hCompletionPort = pParam->hCompletionPort;DWORD dwBytesTransfered;PER_IO_OPERATION_DATA* pIoData;WSAOVERLAPPED* pOverlap;while(true == *pStillRun){dwBytesTransfered = 0;pIoData = 0;pOverlap = 0;BOOL bGetStatus = GetQueuedCompletionStatus(hCompletionPort,&dwBytesTransfered,(PULONG_PTR)&pIoData,&pOverlap,500);if(FALSE == bGetStatus){if(0 == pOverlap)	//did not get a packet from the queue.{continue;	}else{//get a packet for a failed I/O operation.}}if(OPERATION_SEND == pIoData->operationType){if(0 == dwBytesTransfered)	//a packet for a failed I/O operation.{printf("the client %d has close the socket!\n",pIoData->sock);ReleaseIOOperationData(pIoData);}else{// receive operation.pIoData->operationType = OPERATION_RECV;pIoData->wsaBuf.buf = pIoData->message;pIoData->wsaBuf.len = MESSAGE_BUF_SIZE;pIoData->flags = 0;ZeroMemory(&pIoData->overlap,sizeof(pIoData->overlap));int recvRes = WSARecv(pIoData->sock,&pIoData->wsaBuf,1,&pIoData->bytesRecv,&pIoData->flags,&pIoData->overlap,0);if(0 != recvRes && WSA_IO_PENDING != WSAGetLastError()){printf("recv error, may be the client %d has close the socket!\n",pIoData->sock);ReleaseIOOperationData(pIoData);}}}else if(OPERATION_RECV == pIoData->operationType){if(0 == dwBytesTransfered)	//a packet for a failed I/O operation.{printf("the client %d has close the socket!\n",pIoData->sock);ReleaseIOOperationData(pIoData);}else{// show the data receivedpIoData->message[dwBytesTransfered] = '\0';printf("the client %d:%s \n",pIoData->sock,pIoData->message);//send back the data received add a "server:" in the frontchar tempBuf[MESSAGE_BUF_SIZE];sprintf(tempBuf,"server:%s",pIoData->message);strcpy(pIoData->message,tempBuf);pIoData->operationType = OPERATION_SEND;pIoData->wsaBuf.buf = pIoData->message;pIoData->wsaBuf.len = strlen(pIoData->message);int sendRes = WSASend(pIoData->sock,&pIoData->wsaBuf,1,&pIoData->bytesRecv,0,0,0);if(0 == sendRes){pIoData->operationType = OPERATION_RECV;pIoData->wsaBuf.buf = pIoData->message;pIoData->wsaBuf.len = MESSAGE_BUF_SIZE;pIoData->flags = 0;ZeroMemory(&pIoData->overlap,sizeof(pIoData->overlap));int recvRes = WSARecv(pIoData->sock,&pIoData->wsaBuf,1,&pIoData->bytesRecv,&pIoData->flags,&pIoData->overlap,0);if(0 != recvRes && WSA_IO_PENDING != WSAGetLastError()){printf("recv error, may be the client %d has close the socket!\n",pIoData->sock);ReleaseIOOperationData(pIoData);}}else if(SOCKET_ERROR == sendRes && WSA_IO_PENDING == WSAGetLastError()){}else{printf("send error, maybe the client %d has close the socket!\n",pIoData->sock);ReleaseIOOperationData(pIoData);}}}}printf("a completion port thread is exiting!\n");return 0;
}