linux c下简单实现服务端与多客户端同时连接

参考文章：
http://blog.csdn.net/kangroger/article/details/41753605 http://www.cnblogs.com/xudong-bupt/archive/2013/12/29/3483059.html
       对于服务器端来说，通过bind、listen，之后accept建立新的连接。accept返回的句柄建立的连接包括四部分：源IP、源端口号、目的IP、目的端口号。这样在一个应用程序中，就算和多个客户端建立连接，在收到数据后，应用程序通过目的IP和目的端口号也能区分是哪一条连接。

服务端：

#include <sys/types.h>
#include <sys/socket.h>
#include <stdio.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <unistd.h>
#include <string.h>
#include <stdlib.h>
#include <fcntl.h>
#include <sys/shm.h>

#define PORT  8890
#define QUEUE_SIZE   10
#define BUFFER_SIZE 1024

void str_echo(int sockfd)
{
char buffer[BUFFER_SIZE];
pid_t pid = getpid();
while(1)
{
memset(buffer,0,sizeof(buffer));
int len = recv(sockfd, buffer, sizeof(buffer),0);
if(strcmp(buffer,"exit\n")==0)
{
printf("child process: %d exited.\n",pid);
break;
}
printf("pid:%d receive:\n",pid);
fputs(buffer, stdout);
send(sockfd, buffer, len, 0);
}
close(sockfd);
}

int main(int argc, char **argv)
{
//定义IPV4的TCP连接的套接字描述符
int server_sockfd = socket(AF_INET,SOCK_STREAM, 0);

//定义sockaddr_in
struct sockaddr_in server_sockaddr;
server_sockaddr.sin_family = AF_INET;
server_sockaddr.sin_addr.s_addr = htonl(INADDR_ANY);
server_sockaddr.sin_port = htons(PORT);

//bind成功返回0，出错返回-1
if(bind(server_sockfd,(struct sockaddr *)&server_sockaddr,sizeof(server_sockaddr))==-1)
{
perror("bind");
exit(1);//1为异常退出
}
printf("bind success.\n");

//listen成功返回0，出错返回-1，允许同时帧听的连接数为QUEUE_SIZE
if(listen(server_sockfd,QUEUE_SIZE) == -1)
{
perror("listen");
exit(1);
}
printf("listen success.\n");

for(;;)
{
struct sockaddr_in client_addr;
socklen_t length = sizeof(client_addr);
//进程阻塞在accept上，成功返回非负描述字，出错返回-1
int conn = accept(server_sockfd, (struct sockaddr*)&client_addr,&length);
if(conn<0)
{
perror("connect");
exit(1);
}
printf("new client accepted.\n");

pid_t childid;
if(childid=fork()==0)//子进程
{
printf("child process: %d created.\n", getpid());
close(server_sockfd);//在子进程中关闭监听
str_echo(conn);//处理监听的连接
exit(0);
}
}

printf("closed.\n");
close(server_sockfd);
return 0;
}

客户端：

#include <sys/types.h>
#include <sys/socket.h>
#include <stdio.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <unistd.h>
#include <string.h>
#include <stdlib.h>
#include <fcntl.h>
#include <sys/shm.h>

#define PORT  8890
#define BUFFER_SIZE 1024

int main(int argc, char **argv)
{
if(argc!=2)
{
printf("usage: client IP \n");
exit(0);
}

//定义IPV4的TCP连接的套接字描述符
int sock_cli = socket(AF_INET,SOCK_STREAM, 0);

//定义sockaddr_in
struct sockaddr_in servaddr;
memset(&servaddr, 0, sizeof(servaddr));
servaddr.sin_family = AF_INET;
servaddr.sin_addr.s_addr = inet_addr(argv[1]);
servaddr.sin_port = htons(PORT);  //服务器端口

//连接服务器，成功返回0，错误返回-1
if (connect(sock_cli, (struct sockaddr *)&servaddr, sizeof(servaddr)) < 0)
{
perror("connect");
exit(1);
}
printf("connect server(IP:%s).\n",argv[1]);

char sendbuf[BUFFER_SIZE];
char recvbuf[BUFFER_SIZE];
//客户端将控制台输入的信息发送给服务器端，服务器原样返回信息
while (fgets(sendbuf, sizeof(sendbuf), stdin) != NULL)
{
send(sock_cli, sendbuf, strlen(sendbuf),0); ///发送
if(strcmp(sendbuf,"exit\n")==0)
{
printf("client exited.\n");
break;
}
printf("client receive:\n");
recv(sock_cli, recvbuf, sizeof(recvbuf),0); ///接收
fputs(recvbuf, stdout);

memset(sendbuf, 0, sizeof(sendbuf));
memset(recvbuf, 0, sizeof(recvbuf));
}

close(sock_cli);
return 0;
}

server端起来后，端口情况如下：



client1和client2起来后，端口情况如下：



server运行情况如下：



client1运行情况如下：



client2运行情况如下：