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。
