WinSock初学入门：实现TCP服务器

（一）介绍：

　　本文主要采用Winsock API实现了一个Tcp服务器。对初学者而言，相当实用。

　　（二）准备工作：

　　1、使用vc6向导建立控制台工程（console application），并选择支持MFC。

　　2、在stdafx.h中加入头文件conio.h和winsock2.h。

　　3、在头文件中加入：#pragma comment(lib, "ws2_32.lib")。

　　（三）主程序：主要是启动服务器线程并等待用户退出的命令。

int _tmain(int argc, TCHAR* argv[], TCHAR* envp[]) { int nRetCode = 0; cout << "Press ESCAPE to terminate program\r\n"; AfxBeginThread(ServerThread,0); //启动一条线程 while(_getch()!=27); //用户按ESC键则退出 return nRetCode; }

　　（四）线程代码：一个简单的tcp服务器，返回客户的ip地址。

UINT ServerThread(LPVOID pParam) { cout << "Starting up TCP server\r\n"; //A SOCKET is simply a typedef for an unsigned int. //In Unix, socket handles were just about same as file //handles which were again unsigned ints. //Since this cannot be entirely true under Windows //a new data type called SOCKET was defined. //定义一个socket句柄作为服务器 SOCKET server; //WSADATA is a struct that is filled up by the call //to WSAStartup //这是一个结构体，用于调用函数WSAStartup时作为参数 WSADATA wsaData; //The sockaddr_in specifies the address of the socket //for TCP/IP sockets. Other protocols use similar structures. //存放ip地址的结构体 sockaddr_in local; //WSAStartup initializes the program for calling WinSock. //The first parameter specifies the highest version of the //WinSock specification, the program is allowed to use. //初始化winsock，每次必须最先调用 int wsaret=WSAStartup(0x101,&wsaData); //WSAStartup returns zero on success. //If it fails we exit. //测试初始化是否成功 if(wsaret!=0) { return 0; } //Now we populate the sockaddr_in structure //填充服务器的ip地址和端口号 local.sin_family=AF_INET; //Address family local.sin_addr.s_addr=INADDR_ANY; //Wild card IP address local.sin_port=htons((u_short)8888); //port to use //the socket function creates our SOCKET //建立一个tcp socket server=socket(AF_INET,SOCK_STREAM,0); //If the socket() function fails we exit if(server==INVALID_SOCKET) { return 0; } //bind links the socket we just created with the sockaddr_in //structure. Basically it connects the socket with //the local address and a specified port. //If it returns non-zero quit, as this indicates error //绑定服务器的ip地址和端口号 if(bind(server,(sockaddr*)&local,sizeof(local))!=0) { return 0; } //listen instructs the socket to listen for incoming //connections from clients. The second arg is the backlog //监听客户端请求，最大同时连接数10 if(listen(server,10)!=0) { return 0; } //we will need variables to hold the client socket. //thus we declare them here. //接受请求后，实际同客户端socket进行交互的SOCKET client SOCKET client; sockaddr_in from; int fromlen=sizeof(from); while(true)//we are looping endlessly { char temp[512]; //accept() will accept an incoming //client connection //接受一个连接请求，并返回一个同客户端交互的socket给变量client client=accept(server, (struct sockaddr*)&from,&fromlen); //得到客户端的ip地址，并写入缓冲区 sprintf(temp,"Your IP is %s\r\n",inet_ntoa(from.sin_addr)); //we simply send this string to the client // 发送回缓冲中的内容（即：客户端的ip地址） send(client,temp,strlen(temp),0); cout << "Connection from " << inet_ntoa(from.sin_addr) <<"\r\n"; //close the client socket //关闭连接 closesocket(client); } //closesocket() closes the socket and releases the socket descriptor //释放socket资源 closesocket(server); //originally this function probably had some use //currently this is just for backward compatibility //but it is safer to call it as I still believe some //implementations use this to terminate use of WS2_32.DLL //必须作的最后的事 WSACleanup(); return 0; }

　　（五）运行：

　　服务器端：

E:\work\Server\Debug>server Press ESCAPE to terminate program Starting up TCP server Connection from 203.200.100.122 Connection from 127.0.0.1 E:\work\Server\Debug>

　　客户端：

E:\work\Server\Debug>telnet 202.89.211.88 8888 Trying 202.89.211.88... Connected to 202.89.211.88. Escape character is ’^]’. Your IP is 203.200.100.122 Connection closed by foreign host.

　　（六）说明：

　　这只是一个极为简单的tcp server程序，目的是帮助初学者学习winsock编程。因此，程序本着简单的原则，对于很多方面考虑都较少。比如，退出时候可能有socket句柄未释放的危险；只有一条线程，客户端很多时不够实用等等。这些都需要进一步的考虑。

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