1- 简介 客户端获取时间程序--UNIX网络编程

简单来说就是：创建描述符；填充数据；连接服务端；接收数据

sockfd = socket(AF_INET, SOCK_STREAM, 0)


bzero(&servaddr, sizeof(servaddr));


servaddr.sin_family = AF_INET;
servaddr.sin_port   = htons(13)
inet_pton(AF_INET, argv[1], &servaddr.sin_addr)


connect(sockfd, (SA *) &servaddr, sizeof(servaddr))


n = read(sockfd, recvline, MAXLINE)

注意：刚开始创建的listenfd是监听描述符，用于监听特定的端口信息。 后面accept返回的是监听到的服务端socket描述符。

listenfd = Socket(AF_INET, SOCK_STREAM, 0)


bzero(&servaddr, sizeof(servaddr));


servaddr.sin_family      = AF_INET;
servaddr.sin_addr.s_addr = htonl(INADDR_ANY);
servaddr.sin_port        = htons(13);	


Bind(listenfd, (SA *) &servaddr, sizeof(servaddr));


Listen(listenfd, LISTENQ);


connfd = Accept(listenfd, (SA *) NULL, NULL);


Write(connfd, buff, strlen(buff));

#include	"unp.h"

int
main(int argc, char **argv)
{
	int					sockfd, n;
	char				recvline[MAXLINE + 1];
	struct sockaddr_in	servaddr;

	if (argc != 2)
		err_quit("usage: a.out ");

	if ( (sockfd = socket(AF_INET, SOCK_STREAM, 0)) < 0)
		err_sys("socket error");

	bzero(&servaddr, sizeof(servaddr));
	servaddr.sin_family = AF_INET;
	servaddr.sin_port   = htons(13);	
	if (inet_pton(AF_INET, argv[1], &servaddr.sin_addr) <= 0)
		err_quit("inet_pton error for %s", argv[1]);

	if (connect(sockfd, (SA *) &servaddr, sizeof(servaddr)) < 0)
		err_sys("connect error");

	while ( (n = read(sockfd, recvline, MAXLINE)) > 0) {
		recvline[n] = 0;	
		if (fputs(recvline, stdout) == EOF)
			err_sys("fputs error");
	}
	if (n < 0)
		err_sys("read error");

	exit(0);
}

服务端

#include	"unp.h"
#include	

int
main(int argc, char **argv)
{
	int					listenfd, connfd;
	struct sockaddr_in	servaddr;
	char				buff[MAXLINE];
	time_t				ticks;

	listenfd = Socket(AF_INET, SOCK_STREAM, 0);

	bzero(&servaddr, sizeof(servaddr));
	servaddr.sin_family      = AF_INET;
	servaddr.sin_addr.s_addr = htonl(INADDR_ANY);
	servaddr.sin_port        = htons(13);	

	Bind(listenfd, (SA *) &servaddr, sizeof(servaddr));

	Listen(listenfd, LISTENQ);

	for ( ; ; ) {
		connfd = Accept(listenfd, (SA *) NULL, NULL);

        ticks = time(NULL);
        snprintf(buff, sizeof(buff), "%.24srn", ctime(&ticks));
        Write(connfd, buff, strlen(buff));

		Close(connfd);
	}
}

对于TCP/IP指定了某些端口用于特殊服务，参考：TCP/UDP常见端口

我们使用13端口号，就是默认获取时间的端口号是13.

当然我们也可以指定服务端 客户端的端口号为6666。

struct sockaddr_in	servaddr, cliaddr;
Getsockname(sockfd, (SA *) &cliaddr, &len);
printf("local addr: %sn",
		   Sock_ntop((SA *) &cliaddr, sizeof(cliaddr)));



struct sockaddr_in	 cliaddr;
connfd = Accept(listenfd, (SA *) &cliaddr, &len);
printf("connection from %s, port %dn",
			   Inet_ntop(AF_INET, &cliaddr.sin_addr, buff, sizeof(buff)),
			   ntohs(cliaddr.sin_port));