《Windows API巡礼》---listen、accept和connect

listen函数是用来在socket服务器端将套接字置入监听模式并准备接受客户端连接请求：

int listen(

__in SOCKET s, //一个已绑定但尚未连接的套接字

__in int backlog //指定正在等待连接的最大队列长度。如果backlog为3，而有4个客户机

//同时发出连接请求，则前3个放在等待队列中，最后一个将被忽略

);

返回值：

成功时，返回0；

失败时，返回SOCKET_ERROR，调用WSAGetLastError函数查看进一步错误信息。

accept函数用于响应客户端的连接请求：

SOCKET accept(

__in SOCKET s, //处于监听模式的套接字

__out struct sockaddr *addr, //一个有效的sockaddr_in结构的地址，

//函数成功返回时，包含发出连接请求的客户机的IP地址信息

__inout int *addrlen //sockaddr_in结构的长度

);

返回值：

成功时，返回一个新的socket，对应于已经接受的那个客户端连接。对于该客户端所有的后续操作，都使用这个新的套接字；原来的套接字则仍处于监听模式，继续接受其他客户端的连接请求。

失败时，返回INCVALID_SOCKET，调用WSAGetLastError函数查看进一步错误信息。

listen和accept的实例代码如下：

#include <winsock2.h>

#include <stdio.h>

#include <windows.h>

#pragma comment(lib, "wininet.lib")

int main(void) {

//----------------------

// Initialize Winsock.

WSADATA wsaData;

int iResult = WSAStartup(MAKEWORD(2,2), &wsaData);

if (iResult != NO_ERROR) {

printf("Error at WSAStartup()/n");

return 1;

}

//----------------------

// Create a SOCKET for listening for

// incoming connection requests.

SOCKET ListenSocket;

ListenSocket = socket(AF_INET, SOCK_STREAM, IPPROTO_TCP);

if (ListenSocket == INVALID_SOCKET) {

printf("Error at socket(): %ld/n", WSAGetLastError());

WSACleanup();

return 1;

}

//----------------------

// The sockaddr_in structure specifies the address family,

// IP address, and port for the socket that is being bound.

sockaddr_in service;

service.sin_family = AF_INET;

service.sin_addr.s_addr = inet_addr("127.0.0.1");

service.sin_port = htons(27015);

if (bind( ListenSocket,

(SOCKADDR*) &service,

sizeof(service)) == SOCKET_ERROR) {

printf("bind() failed./n");

closesocket(ListenSocket);

WSACleanup();

return 1;

}

//----------------------

// Listen for incoming connection requests.

// on the created socket

if (listen( ListenSocket, 1 ) == SOCKET_ERROR) {

printf("Error listening on socket./n");

closesocket(ListenSocket);

WSACleanup();

return 1;

}

//----------------------

// Create a SOCKET for accepting incoming requests.

SOCKET AcceptSocket;

printf("Waiting for client to connect.../n");

//----------------------

// Accept the connection.

AcceptSocket = accept( ListenSocket, NULL, NULL );

if (AcceptSocket == INVALID_SOCKET) {

printf("accept failed: %d/n", WSAGetLastError());

closesocket(ListenSocket);

WSACleanup();

return 1;

} else

printf("Client connected./n");

// No longer need server socket

closesocket(ListenSocket);

WSACleanup();

return 0;

}

connect函数用于客户端与网络中的服务器建立连接：

int connect(

__in SOCKET s, //进行连接的套接字

__in const struct sockaddr *name, //要连接服务器的套接字地址结构

__in int namelen //name的长度

);

返回值：

成功时，返回0；

失败时，返回SOCKET_ERROR，调用WSAGetLastError函数查看进一步错误信息。

connect的实例代码如下：

#include <stdio.h>

#include "winsock2.h"

#include <windows.h>

#pragma comment(lib, "wininet.lib")

void main() {

//----------------------

// Initialize Winsock

WSADATA wsaData;

int iResult = WSAStartup(MAKEWORD(2,2), &wsaData);

if (iResult != NO_ERROR)

printf("Error at WSAStartup()/n");

//----------------------

// Create a SOCKET for connecting to server

SOCKET ConnectSocket;

ConnectSocket = socket(AF_INET, SOCK_STREAM, IPPROTO_TCP);

if (ConnectSocket == INVALID_SOCKET) {

printf("Error at socket(): %ld/n", WSAGetLastError());

WSACleanup();

return;

}

//----------------------

// The sockaddr_in structure specifies the address family,

// IP address, and port of the server to be connected to.

sockaddr_in clientService;

clientService.sin_family = AF_INET;

clientService.sin_addr.s_addr = inet_addr( "127.0.0.1" );

clientService.sin_port = htons( 27015 );

//----------------------

// Connect to server.

if ( connect( ConnectSocket, (SOCKADDR*) &clientService, sizeof(clientService) ) == SOCKET_ERROR) {

printf( "Failed to connect./n" );

WSACleanup();

return;

}

printf("Connected to server./n");

WSACleanup();

return;

}