1.确保服务端在相应的端口监听；
2.关闭防火墙（ubuntu下面的命令：sudo ufw disable）;
3.而且server端要 sudo 运行；
UNP第一个小程序（有些异常没有捕获）：
客户端：
int
main(int argc, char **argv)
{
int sockfd, n;
char recvline[MAXLINE + 1];
struct sockaddr_in servaddr;
if (argc != 2)
{printf("usage: a.out <IPaddress>");exit(-1);}
if ( (sockfd = socket(AF_INET, SOCK_STREAM, 0)) < 0)
{printf("socket error");exit(-1);}
bzero(&servaddr, sizeof(servaddr));
servaddr.sin_family = AF_INET;
servaddr.sin_port = htons(1000); /* daytime server */
if (inet_pton(AF_INET, argv[1], &servaddr.sin_addr) <= 0)
{printf("inet_pton error for %s", argv[1]);exit(-1);}
if (connect(sockfd, (struct sockaddr *) &servaddr, sizeof(servaddr)) < 0)
{perror("connect error");exit(-1);}
while ( (n = read(sockfd, recvline, MAXLINE)) > 0) {
recvline[n] = 0; /* null terminate */
if (fputs(recvline, stdout) == EOF)
{printf("fputs error!");exit(-1);};
}
if (n < 0)
{printf("client read error");exit(-1);}
exit(0);
}
服务器端：
#include<time.h>
#include<stdio.h>
#include<stdlib.h>
#include<netinet/in.h>
#include<arpa/inet.h>
#include<sys/socket.h>
#include<string.h>
#define MAXLINE 100
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(1000); /* daytime server */
bind(listenfd, (struct sockaddr *) &servaddr, sizeof(servaddr));
listen(listenfd,3);
for ( ; ; ) {
connfd = accept(listenfd, (struct sockaddr *) NULL, NULL);
ticks = time(NULL);
snprintf(buff, sizeof(buff), "%.24s\r\n", ctime(&ticks));
if(write(connfd, buff, strlen(buff)) != strlen(buff))
{printf("server write error!");exit(-1);}
close(connfd);
}
}
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