Linux网络客户端编程

1. linux下Socket编程 怎样实现客户端之间互相通信

1. 网络的Socket数据传输是一种特殊的I/O，Socket也是一种文件描述符。Socket也具有一个类似于打开文件的函数调用Socket()，该函数返回一个整型的Socket描述符，随后的连接建立、数据传输等操作都是通过该Socket实现的。

2. 下面用Socket实现一个windows下的c语言socket通信例子，这里我们客户端传递一个字符串，服务器端进行接收。

【服务器端】
#include"stdafx.h"
#include<stdio.h>
#include<winsock2.h>
#include<winsock2.h>
#defineSERVER_PORT5208//侦听端口
voidmain()
{
WORDwVersionRequested;
WSADATAwsaData;
intret,nLeft,length;
SOCKETsListen,sServer;//侦听套接字，连接套接字
structsockaddr_insaServer,saClient;//地址信息
char*ptr;//用于遍历信息的指针
//WinSock初始化
wVersionRequested=MAKEWORD(2,2);//希望使用的WinSockDLL的版本
ret=WSAStartup(wVersionRequested,&wsaData);
if(ret!=0)
{
printf("WSAStartup()failed!
");
return;
}
//创建Socket,使用TCP协议
sListen=socket(AF_INET,SOCK_STREAM,IPPROTO_TCP);
if(sListen==INVALID_SOCKET)
{
WSACleanup();
printf("socket()faild!
");
return;
}
//构建本地地址信息
saServer.sin_family=AF_INET;//地址家族
saServer.sin_port=htons(SERVER_PORT);//注意转化为网络字节序
saServer.sin_addr.S_un.S_addr=htonl(INADDR_ANY);//使用INADDR_ANY指示任意地址

//绑定
ret=bind(sListen,(structsockaddr*)&saServer,sizeof(saServer));
if(ret==SOCKET_ERROR)
{
printf("bind()faild!code:%d
",WSAGetLastError());
closesocket(sListen);//关闭套接字
WSACleanup();
return;
}

//侦听连接请求
ret=listen(sListen,5);
if(ret==SOCKET_ERROR)
{
printf("listen()faild!code:%d
",WSAGetLastError());
closesocket(sListen);//关闭套接字
return;
}

printf("Waitingforclientconnecting!
");
printf("Tips:Ctrl+ctoquit!
");
//阻塞等待接受客户端连接
while(1)//循环监听客户端，永远不停止，所以，在本项目中，我们没有心跳包。
{
length=sizeof(saClient);
sServer=accept(sListen,(structsockaddr*)&saClient,&length);
if(sServer==INVALID_SOCKET)
{
printf("accept()faild!code:%d
",WSAGetLastError());
closesocket(sListen);//关闭套接字
WSACleanup();
return;
}
charreceiveMessage[5000];
nLeft=sizeof(receiveMessage);
ptr=(char*)&receiveMessage;
while(nLeft>0)
{
//接收数据
ret=recv(sServer,ptr,5000,0);
if(ret==SOCKET_ERROR)
{
printf("recv()failed!
");
return;
}
if(ret==0)//客户端已经关闭连接
{
printf("Clienthasclosedtheconnection
");
break;
}
nLeft-=ret;
ptr+=ret;
}
printf("receivemessage:%s
",receiveMessage);//打印我们接收到的消息。

}
//closesocket(sListen);
//closesocket(sServer);
//WSACleanup();
}
【客户端】
#include"stdafx.h"
#include<stdio.h>
#include<stdlib.h>
#include<winsock2.h>
#defineSERVER_PORT5208//侦听端口
voidmain()
{
WORDwVersionRequested;
WSADATAwsaData;
intret;
SOCKETsClient;//连接套接字
structsockaddr_insaServer;//地址信息
char*ptr;
BOOLfSuccess=TRUE;
//WinSock初始化
wVersionRequested=MAKEWORD(2,2);//希望使用的WinSockDLL的版本
ret=WSAStartup(wVersionRequested,&wsaData);
if(ret!=0)
{
printf("WSAStartup()failed!
");
return;
}
//确认WinSockDLL支持版本2.2
if(LOBYTE(wsaData.wVersion)!=2||HIBYTE(wsaData.wVersion)!=2)
{
WSACleanup();
printf("InvalidWinSockversion!
");
return;
}
//创建Socket,使用TCP协议
sClient=socket(AF_INET,SOCK_STREAM,IPPROTO_TCP);
if(sClient==INVALID_SOCKET)
{
WSACleanup();
printf("socket()failed!
");
return;
}
//构建服务器地址信息
saServer.sin_family=AF_INET;//地址家族
saServer.sin_port=htons(SERVER_PORT);//注意转化为网络节序
saServer.sin_addr.S_un.S_addr=inet_addr("192.168.1.127");
//连接服务器
ret=connect(sClient,(structsockaddr*)&saServer,sizeof(saServer));
if(ret==SOCKET_ERROR)
{
printf("connect()failed!
");
closesocket(sClient);//关闭套接字
WSACleanup();
return;
}


charsendMessage[]="hellothisisclientmessage!";
ret=send(sClient,(char*)&sendMessage,sizeof(sendMessage),0);
if(ret==SOCKET_ERROR)
{
printf("send()failed!
");
}
else
printf("clientinfohasbeensent!");
closesocket(sClient);//关闭套接字
WSACleanup();
}

2. 现在想把linux网络编程中TCP客户端端口固定了，这个要怎么做才能使客户端固定呢

socket的编程流程为
...
socket()
bind()

//很多人在编客户端的时候没有进行bind（），实际上是可以bind的，不过不bind后就会系统自动分配端口

connect()
...
这样你改改试试，应该是可以的

3. unix/linux网络编程开发和unix/linux服务器开发有什么区别

1、unix/linux网络编程是一类编程技术（一般指socket相关的编程）。
2、unix/linux服务器是一种服务系统（它是指向客户端提供某种服务的一套应用系统，如ftp服务器、http服务器等）。
3、unix/linux服务器的开发（一套应用系统的开发）通常要用到unix/linux网络编程技术。

4. linux下socket 网络编程(客户端向服务器端发送文件) 求源代码 大哥大姐帮帮忙 。。谢谢

server:

#include <stdio.h>
#include <errno.h>
#include <unistd.h>
#include <signal.h>
#include <stdlib.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <arpa/inet.h>
#include <netinet/in.h>
#include <syslog.h>
#include <sys/time.h>
#include <string.h>
#include <fcntl.h>
#include <sys/wait.h>

#define MAXDATASIZE 1024
#define SERVPORT 19999
#define BACKLOG 10

int SendFileToServ(const char *path, const char *FileName, const char *ip)
{
#define PORT 20002
int sockfd;
int recvbytes;
char buf[MAXDATASIZE];
char send_str[MAXDATASIZE];
char filepath[128] = {0};
struct sockaddr_in serv_addr;
FILE *fp;
sprintf(filepath, "%s%s", path, FileName);

if((sockfd=socket(AF_INET,SOCK_STREAM,0))==-1)
{
perror("socket");
return 1;
}
bzero(&serv_addr,sizeof(struct sockaddr_in));
serv_addr.sin_family=AF_INET;
serv_addr.sin_port=htons(PORT);
inet_aton(ip, &serv_addr.sin_addr);
int IErrCount = 0;
again:
if(connect(sockfd,(struct sockaddr *)&serv_addr,sizeof(struct sockaddr))==-1)
{
if (5 == IErrCount)
return 1;
IErrCount++;
perror("connect");
sleep(2);
goto again;
}
//if ((fp = fopen(FileName, "rb")) == NULL)
if ((fp = fopen(filepath, "rb")) == NULL)
{
perror("fopen ");
return 1;
}
recvbytes = write(sockfd, FileName, strlen(FileName));
recvbytes = read(sockfd, buf, MAXDATASIZE);
if (!memcmp(buf, "sendmsg", 7))
{
while(fgets(send_str, MAXDATASIZE, fp))
{
recvbytes = write(sockfd, send_str, strlen(send_str));
recvbytes = read(sockfd, buf, MAXDATASIZE);
if (recvbytes <= 0)
{
fclose(fp);
close(sockfd);
return 1;
}
if (memcmp(buf, "goon", 4))
{
fclose(fp);
close(sockfd);
return 1;
}
}
recvbytes = write(sockfd, "end", 3);
}
else
{
fclose(fp);
close(sockfd);
return 1;
}
memset(buf, 0, MAXDATASIZE);
if (read(sockfd, buf, MAXDATASIZE) <= 0)
{
close(sockfd);
return 2;
}
char *Eptr = "nginx reload error";
//printf("bf[%s]\n", buf);
int ret;
ret = strncmp(buf, Eptr, strlen(Eptr));
//printf("%d\n", ret);
if (!ret)
{
close(sockfd);
return 2;
}

close(sockfd);
return 0;
}

int mysyslog(const char * msg)
{
FILE *fp;
if ((fp = fopen("/tmp/tmp.log", "a+")) == NULL)
{
return 0;
}
fprintf(fp, "[%s]\n", msg);
fclose(fp);
return 0;
}
static void quit_handler(int signal)
{
kill(0, SIGUSR2);
syslog( LOG_NOTICE, "apuserv quit...");
// do something exit thing ,such as close socket ,close mysql,free list
// .....
//i end
exit(0);
}
static int re_conf = 0;
static void reconf_handler(int signal)
{
re_conf=1;
syslog(LOG_NOTICE,"apuserv reload configure file .");
// 请在循环体中判断，如果re_conf == 1，请再次加载配置文件。
}
static int isrunning(void)
{
int fd;
int ret;
struct flock lock;
lock.l_type = F_WRLCK;
lock.l_whence = 0;
lock.l_start = 0;
lock.l_len = 0;
const char *lckfile = "/tmp/apuserv.lock";
fd = open(lckfile,O_WRONLY|O_CREAT);
if (fd < 0) {
syslog(LOG_ERR,"can not create lock file: %s\n",lckfile);
return 1;
}
if ((ret = fcntl(fd,F_SETLK,&lock)) < 0) {
ret = fcntl(fd,F_GETLK,&lock);
if (lock.l_type != F_UNLCK) {
close(fd);
return lock.l_pid;
}
else {
fcntl(fd,F_SETLK,&lock);
}
}
return 0;
}

int MyHandleBuff(const char *buf, char *str, char *FileName, char *pth)
{
sscanf(buf, "%s %s %s", pth, FileName, str);
printf("path=%s\nfilename=%s\nip=%s\n", pth, FileName, str);
return 0;
}

int main(int argc, char **argv)
{
int sockfd,client_fd;
socklen_t sin_size;
struct sockaddr_in my_addr,remote_addr;
char buff[MAXDATASIZE];
int recvbytes;
#if 1
int pid ;
char ch ;
int ret;
int debug = 0;
signal(SIGUSR1, SIG_IGN);
signal(SIGUSR2, SIG_IGN);
signal(SIGHUP, SIG_IGN);
signal(SIGTERM, quit_handler);
syslog(LOG_NOTICE,"apuserver start....");
while ((ch = getopt(argc, argv, "dhV")) != -1) {
switch (ch) {
case 'd':
debug = 1;
break;
case 'V':
printf("Version:%s\n","1.0.0");
return 0;
case 'h':
printf(" -d use daemon mode\n");
printf(" -V show version\n");
return 0;
default:
printf(" -d use daemon mode\n");
printf(" -V show version\n");
}
}
if (debug && daemon(0,0 ) ) {
return -1;
}
if (isrunning()) {
fprintf(stderr, "apuserv is already running\n");
syslog(LOG_INFO,"apuserv is already running\n");
exit(0);
}
while (1) {
pid = fork();
if (pid < 0)
return -1;
if (pid == 0)
break;
while ((ret = waitpid(pid, NULL, 0)) != pid) {
syslog(LOG_NOTICE, "waitpid want %d, but got %d", pid, ret);
if (ret < 0)
syslog(LOG_NOTICE, "waitpid errno:%d", errno);
}
kill(0, SIGUSR2);
sleep(1);
syslog(LOG_NOTICE,"restart apuserver");
}
signal(SIGHUP, reconf_handler);
signal(SIGPIPE, SIG_IGN);
signal(SIGUSR1,SIG_IGN);
signal(SIGUSR2, SIG_DFL);
signal(SIGTERM, SIG_DFL);
#endif
if((sockfd=socket(AF_INET,SOCK_STREAM,0))==-1)
{
perror("socket");
exit(1);
}

bzero(&my_addr,sizeof(struct sockaddr_in));
my_addr.sin_family=AF_INET;
my_addr.sin_port=htons(SERVPORT);
my_addr.sin_addr.s_addr = htonl(INADDR_ANY);
if(bind(sockfd,(struct sockaddr *)&my_addr,sizeof(struct sockaddr))==-1)
{
perror("bind");
exit(1);
}
if(listen(sockfd,BACKLOG)==-1)
{
perror("listen");
exit(1);
}
int nret;
while(1)
{
sin_size = sizeof(struct sockaddr_in);
if((client_fd = accept(sockfd, (struct sockaddr *)&remote_addr, &sin_size))==-1)
{
perror("falied accept");
continue;
}
memset(buff, 0, MAXDATASIZE);
recvbytes = read(client_fd, buff, MAXDATASIZE);
char str[16] = {0};
char FileName[128] = {0};
char path[128] = {0};
MyHandleBuff(buff, str, FileName, path);
if (recvbytes > 0)
{
nret = SendFileToServ(path, FileName, str);
printf("nret[%d]\n", nret);
if (1 == nret)
write(client_fd, "send file error", 15);
else if(2 == nret)
write(client_fd, "reload nginx error", 18);
else
write(client_fd, "succ", 4);
}
close(client_fd);
}
}
_________________________________________________
client:
#include <stdio.h>
#include <errno.h>
#include <unistd.h>
#include <signal.h>
#include <stdlib.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <arpa/inet.h>
#include <netinet/in.h>
#include <syslog.h>
#include <sys/time.h>
#include <string.h>
#include <fcntl.h>
#include <sys/wait.h>

#define MAXDATASIZE 1024
#define SERVPORT 20002
#define BACKLOG 10

int mysyslog(const char * msg)
{
FILE *fp;
if ((fp = fopen("/tmp/tmp.log", "a+")) == NULL)
{
return 0;
}
fprintf(fp, "[%s]\n", msg);
fclose(fp);
return 0;
}
static void quit_handler(int signal)
{
kill(0, SIGUSR2);
syslog( LOG_NOTICE, "apuserv quit...");
// do something exit thing ,such as close socket ,close mysql,free list
// .....
//i end
exit(0);
}
static int re_conf = 0;
static void reconf_handler(int signal)
{
re_conf=1;
syslog(LOG_NOTICE,"apuserv reload configure file .");
// ????·???????1nf == 1￡???′μ?????

static int isrunning(void)
{
int fd;
int ret;
struct flock lock;
lock.l_type = F_WRLCK;
lock.l_whence = 0;
lock.l_start = 0;
lock.l_len = 0;
const char *lckfile = "/tmp/dstserver.lock";
fd = open(lckfile,O_WRONLY|O_CREAT);
if (fd < 0) {
syslog(LOG_ERR,"can not create lock file: %s\n",lckfile);
return 1;
}
if ((ret = fcntl(fd,F_SETLK,&lock)) < 0) {
ret = fcntl(fd,F_GETLK,&lock);
if (lock.l_type != F_UNLCK) {
close(fd);
return lock.l_pid;
}
else {
fcntl(fd,F_SETLK,&lock);
}
}
return 0;
}

int main(int argc, char **argv)
{
int sockfd,client_fd;
socklen_t sin_size;
struct sockaddr_in my_addr,remote_addr;
char buff[MAXDATASIZE];
int recvbytes;
#if 1
int pid ;
char ch ;
int ret;
int debug = 0;
signal(SIGUSR1, SIG_IGN);
signal(SIGUSR2, SIG_IGN);
signal(SIGHUP, SIG_IGN);
signal(SIGTERM, quit_handler);
syslog(LOG_NOTICE,"dstserver start....");

while ((ch = getopt(argc, argv, "dhV")) != -1) {
switch (ch) {
case 'd':
debug = 1;
break;
case 'V':
printf("Version:%s\n","1.0.0");
return 0;
case 'h':
printf(" -d use daemon mode\n");
printf(" -V show version\n");
return 0;
default:
printf(" -d use daemon mode\n");
printf(" -V show version\n");
}
}
if (debug && daemon(0,0 ) ) {
return -1;
}
if (isrunning()) {
fprintf(stderr, "dstserver is already running\n");
syslog(LOG_INFO,"dstserver is already running\n");
exit(0);
}
while (1) {
pid = fork();
if (pid < 0)
return -1;
if (pid == 0)
break;
while ((ret = waitpid(pid, NULL, 0)) != pid) {
syslog(LOG_NOTICE, "waitpid want %d, but got %d", pid, ret);
if (ret < 0)
syslog(LOG_NOTICE, "waitpid errno:%d", errno);
}
kill(0, SIGUSR2);
sleep(1);
syslog(LOG_NOTICE,"restart apuserver");
}
signal(SIGHUP, reconf_handler);
signal(SIGPIPE, SIG_IGN);
signal(SIGUSR1,SIG_IGN);
signal(SIGUSR2, SIG_DFL);
signal(SIGTERM, SIG_DFL);
#endif
if((sockfd=socket(AF_INET,SOCK_STREAM,0))==-1)
{
perror("socket");
exit(1);
}

bzero(&my_addr,sizeof(struct sockaddr_in));
my_addr.sin_family=AF_INET;
my_addr.sin_port=htons(SERVPORT);
my_addr.sin_addr.s_addr = htonl(INADDR_ANY);
if(bind(sockfd,(struct sockaddr *)&my_addr,sizeof(struct sockaddr))==-1)
{
perror("bind");
exit(1);
}
if(listen(sockfd,BACKLOG)==-1)
{
perror("listen");
exit(1);
}

char filepath[MAXDATASIZE]= {0};
FILE *fp;
while(1)
{
sin_size = sizeof(struct sockaddr_in);
if((client_fd = accept(sockfd, (struct sockaddr *)&remote_addr, &sin_size))==-1)
{
perror("falied accept");
continue;
}
memset(buff, 0, MAXDATASIZE);
recvbytes = read(client_fd, buff, MAXDATASIZE);
sprintf(filepath, "/etc/nginx/url_rule/%s", buff);
if ((fp = fopen(filepath, "wb")) == NULL)
{
perror("fopen");
close(client_fd);
continue;
}
write(client_fd, "sendmsg", 7);
while(read(client_fd, buff, MAXDATASIZE))
{
if (!memcmp(buff, "end", 3))
{
fclose(fp);
break;
}
else
{
fprintf(fp, "%s", buff);
write(client_fd, "goon", 4);
}
}
//system("nginx -s reload");
char *Sptr = "nginx reload succ";
char *Eptr = "nginx reload error";
int ret;
ret = system("nginx -s reload");
printf("ret[%d]\n", ret);
if (ret != 0)
{
write(client_fd, Eptr, strlen(Eptr));
}
else
{
write(client_fd, Sptr, strlen(Sptr));
}
close(client_fd);
}
}

以前写的：内容忘记了。不是很复杂你可以自己看！

5. linux tcp/ip 网络通信编程

/*************************************
文件名：server.c
linux下socket网络编程简例-服务端程序
服务器端口设为0x8888（端口和地址可根据实际情况更改，或者使用参数传入）
服务器地址设为192.168.1.104
作者:kikilizhm#163.com(将#换为@)
*/
#include<stdlib.h>
#include<sys/types.h>
#include<stdio.h>
#include<sys/socket.h>
#include<linux/in.h>
#include<string.h>
intmain()
{
intsfp,nfp;/*定义两个描述符*/
structsockaddr_ins_add,c_add;
intsin_size;
unsignedshortportnum=0x8888;/*服务端使用端口*/
printf("Hello,welcometomyserver!
");
sfp=socket(AF_INET,SOCK_STREAM,0);
if(-1==sfp)
{
printf("socketfail!
");
return-1;
}
printf("socketok!
");
/*填充服务器端口地址信息，以便下面使用此地址和端口监听*/
bzero(&s_add,sizeof(structsockaddr_in));
s_add.sin_family=AF_INET;
s_add.sin_addr.s_addr=htonl(INADDR_ANY);/*这里地址使用全0，即所有*/
s_add.sin_port=htons(portnum);
/*使用bind进行绑定端口*/
if(-1==bind(sfp,(structsockaddr*)(&s_add),sizeof(structsockaddr)))
{
printf("bindfail!
");
return-1;
}
printf("bindok!
");
/*开始监听相应的端口*/
if(-1==listen(sfp,5))
{
printf("listenfail!
");
return-1;
}
printf("listenok
");
while(1)
{
sin_size=sizeof(structsockaddr_in);
/*accept服务端使用函数，调用时即进入阻塞状态，等待用户进行连接，在没有客户端进行连接时，程序停止在此处，
不会看到后面的打印，当有客户端进行连接时，程序马上执行一次，然后再次循环到此处继续等待。
此处accept的第二个参数用于获取客户端的端口和地址信息。
*/
nfp=accept(sfp,(structsockaddr*)(&c_add),&sin_size);
if(-1==nfp)
{
printf("acceptfail!
");
return-1;
}
printf("acceptok!
Serverstartgetconnectfrom%#x:%#x
",ntohl(c_add.sin_addr.s_addr),ntohs(c_add.sin_port));
/*这里使用write向客户端发送信息，也可以尝试使用其他函数实现*/
if(-1==write(nfp,"hello,welcometomyserver
",32))
{
printf("writefail!
");
return-1;
}
printf("writeok!
");
close(nfp);
}
close(sfp);
return0;
}

/*************************************
文件名：client.c
linux下socket网络编程简例-客户端程序
服务器端口设为0x8888（端口和地址可根据实际情况更改，或者使用参数传入）
服务器地址设为192.168.1.104
作者:kikilizhm#163.com(将#换为@)
*/
#include<stdlib.h>
#include<sys/types.h>
#include<stdio.h>
#include<sys/socket.h>
#include<linux/in.h>
#include<string.h>
intmain()
{
intcfd;/*文件描述符*/
intrecbytes;
intsin_size;
charbuffer[1024]={0};/*接受缓冲区*/
structsockaddr_ins_add,c_add;/*存储服务端和本端的ip、端口等信息结构体*/
unsignedshortportnum=0x8888;/*服务端使用的通信端口，可以更改，需和服务端相同*/
printf("Hello,welcometoclient!
");
/*建立socket使用因特网，TCP流传输*/
cfd=socket(AF_INET,SOCK_STREAM,0);
if(-1==cfd)
{
printf("socketfail!
");
return-1;
}
printf("socketok!
");
/*构造服务器端的ip和端口信息，具体结构体可以查资料*/
bzero(&s_add,sizeof(structsockaddr_in));
s_add.sin_family=AF_INET;
s_add.sin_addr.s_addr=inet_addr("192.168.1.104");/*ip转换为4字节整形，使用时需要根据服务端ip进行更改*/
s_add.sin_port=htons(portnum);/*这里htons是将short型数据字节序由主机型转换为网络型，其实就是
将2字节数据的前后两个字节倒换，和对应的ntohs效果、实质相同，只不过名字不同。htonl和ntohl是
操作的4字节整形。将0x12345678变为0x78563412，名字不同，内容两两相同，一般情况下网络为大端，
PPC的cpu为大端，x86的cpu为小端，arm的可以配置大小端，需要保证接收时字节序正确。
*/
printf("s_addr=%#x,port:%#x
",s_add.sin_addr.s_addr,s_add.sin_port);/*这里打印出的是小端
和我们平时看到的是相反的。*/
/*客户端连接服务器，参数依次为socket文件描述符，地址信息，地址结构大小*/
if(-1==connect(cfd,(structsockaddr*)(&s_add),sizeof(structsockaddr)))
{
printf("connectfail!
");
return-1;
}
printf("connectok!
");
/*连接成功,从服务端接收字符*/
if(-1==(recbytes=read(cfd,buffer,1024)))
{
printf("readdatafail!
");
return-1;
}
printf("readok
REC:
");
buffer[recbytes]='';
printf("%s
",buffer);
getchar();/*此句为使程序暂停在此处，可以使用netstat查看当前的连接*/
close(cfd);/*关闭连接，本次通信完成*/
return0;
}

6. LINUX网络编程TCP服务器 客户端 有乱码怎么解决

解决办法:
1.在客户端n=read(socketfd,buff,1023);代码之前加上memset(buff,0,sizeof(buff));，这是保证收到较短数据(使用TCP你不能保证每次接收的数据和发送的数据时等长的)，打印也是正确的;
2.将客户端buff[n+1]+='\0';修改为buff[n]='\0';，这是因为n是下标，已经是最后一个位置了;
3.将服务器端buff[n+1]+='\0';修改为buff[n]='\0';，这是因为n是下标，已经是最后一个位置了，而且和第2)一样，那个加号也要去掉，应该是笔误吧;
4.最大的问题，将服务器端write(connectfd,buff,1023);，你怎么能够保证收到1023个字符呢?也应该将while中条件移出作为WHILE中的一条语句，而且加上前面所述的memset语句，而将这里的write(connectfd,buff,1023);修改为write(connectfd,buff,strlen(buff))。
祝共同进步!

7. linux下socket 网络编程(客户端向服务器端发送文件) 求源代码 大哥大姐帮帮忙 ,。。谢谢

源代码奉上，流程图。。。这个太简单了，你自己看看。。。。。。。

//TCP
//服务器端程序
#include< stdio.h >
#include< stdlib.h >
#include< windows.h >
#include< winsock.h >
#include< string.h >

#pragma comment( lib, "ws2_32.lib" )

#define PORT 2046
#define BACKLOG 10
#define TRUE 1

void main( void )
{
int iServerSock;
int iClientSock;

char *buf = "hello, world!\n";

struct sockaddr_in ServerAddr;
struct sockaddr_in ClientAddr;

int sin_size;

WSADATA WSAData;

if( WSAStartup( MAKEWORD( 1, 1 ), &WSAData ) )//初始化
{
printf( "initializationing error!\n" );
WSACleanup( );
exit( 0 );
}

if( ( iServerSock = socket( AF_INET, SOCK_STREAM, 0 ) ) == INVALID_SOCKET )
{
printf( "创建套接字失败!\n" );
WSACleanup( );
exit( 0 );
}

ServerAddr.sin_family = AF_INET;
ServerAddr.sin_port = htons( PORT );//监视的端口号
ServerAddr.sin_addr.s_addr = INADDR_ANY;//本地IP
memset( & ( ServerAddr.sin_zero ), 0, sizeof( ServerAddr.sin_zero ) );

if( bind( iServerSock, ( struct sockaddr * )&ServerAddr, sizeof( struct sockaddr ) ) == -1 )
{
printf( "bind调用失败!\n" );
WSACleanup( );
exit( 0 );
}

if( listen( iServerSock, BACKLOG ) == -1 )
{
printf( "listen调用失败!\n" );
WSACleanup( );
exit( 0 );
}

while( TRUE )
{
sin_size = sizeof( struct sockaddr_in );
iClientSock = accept( iServerSock, ( struct sockaddr * )&ClientAddr, &sin_size );

if( iClientSock == -1 )
{
printf( "accept调用失败!\n" );
WSACleanup( );
exit( 0 );
}

printf( "服务器连接到%s\n", inet_ntoa( ClientAddr.sin_addr ) );
if( send( iClientSock, buf, strlen( buf ), 0 ) == -1 )
{
printf( "send调用失败!" );
closesocket( iClientSock );
WSACleanup( );
exit( 0 );
}
}
}

/////客户端程序
#include< stdio.h >
#include< stdlib.h >
#include< windows.h >
#include< winsock.h >
#include< string.h >

#pragma comment( lib, "ws2_32.lib" )

#define PORT 2046
#define BACKLOG 10
#define TRUE 1
#define MAXDATASIZE 100

void main( void )
{

int iClientSock;
char buf[ MAXDATASIZE ];
struct sockaddr_in ServerAddr;
int numbytes;
// struct hostent *he;
WSADATA WSAData;

// int sin_size;

/* if( ( he = gethostbyname( "liuys" ) ) == NULL )
{
printf( "gethostbyname调用失败!" );
WSACleanup( );
exit( 0 );
}
*/

if( WSAStartup( MAKEWORD( 1, 1 ), &WSAData ) )//初始化
{
printf( "initializationing error!\n" );
WSACleanup( );
exit( 0 );
}

if( ( iClientSock = socket( AF_INET, SOCK_STREAM, 0 ) ) == INVALID_SOCKET )
{
printf( "创建套接字失败!\n" );
WSACleanup( );
exit( 0 );
}

ServerAddr.sin_family = AF_INET;
ServerAddr.sin_port = htons( PORT );
// ServerAddr.sin_addr = *( ( struct in_addr * )he->h_addr );
ServerAddr.sin_addr.s_addr = inet_addr( "192.168.2.194" );//记得换IP
memset( &( ServerAddr.sin_zero ), 0, sizeof( ServerAddr.sin_zero ) );

if( connect( iClientSock, ( struct sockaddr * ) & ServerAddr, sizeof( struct sockaddr ) ) == -1 )
{
printf( "connect失败!" );
WSACleanup( );
exit( 0 );
}

numbytes = recv( iClientSock, buf, MAXDATASIZE, 0 );

if( numbytes == -1 )
{
printf( "recv失败!" );
WSACleanup( );
exit( 0 );
}

buf[ numbytes ] = '\0';

printf( "Received: %s", buf );

closesocket( iClientSock );
WSACleanup( );
}

/////UDP
//服务器
#include< stdio.h >
#include< string.h >
#include< winsock.h >
#include< windows.h >

#pragma comment( lib, "ws2_32.lib" )

#define PORT 2046
#define BACKLOG 10
#define TRUE 1
#define MAXDATASIZE 1000

void main( void )
{
int iServerSock;
// int iClientSock;

int addr_len;
int numbytes;

char buf[ MAXDATASIZE ];

struct sockaddr_in ServerAddr;
struct sockaddr_in ClientAddr;

WSADATA WSAData;
if( WSAStartup( MAKEWORD( 1, 1 ), &WSAData ) )
{
printf( "initializationing error!\n" );
WSACleanup( );
exit( 0 );
}

iServerSock = socket( AF_INET, SOCK_DGRAM, 0 );
if( iServerSock == INVALID_SOCKET )
{
printf( "创建套接字失败!\n" );
WSACleanup( );
exit( 0 );
}

ServerAddr.sin_family = AF_INET;
ServerAddr.sin_port = htons( PORT );//监视的端口号
ServerAddr.sin_addr.s_addr = INADDR_ANY;//本地IP
memset( & ( ServerAddr.sin_zero ), 0, sizeof( ServerAddr.sin_zero ) );

if( bind( iServerSock, ( struct sockaddr * )&ServerAddr, sizeof( struct sockaddr ) ) == -1 )
{
printf( "bind调用失败!\n" );
WSACleanup( );
exit( 0 );
}

addr_len = sizeof( struct sockaddr );
numbytes = recvfrom( iServerSock, buf, MAXDATASIZE, 0, ( struct sockaddr * ) & ClientAddr, &addr_len );
if( numbytes == -1 )
{
printf( "recvfrom调用失败!\n" );
WSACleanup( );
exit( 0 );
}

printf( "got packet from %s\n", inet_ntoa( ClientAddr.sin_addr ) );
printf( "packet is %d bytes long\n", numbytes );
buf[ numbytes ] = '\0';
printf( "packet contains \"%s\"\n", buf );

closesocket( iServerSock );
WSACleanup( );

}
//客户端
#include< stdio.h >
#include< stdlib.h >
#include< windows.h >
#include< winsock.h >
#include< string.h >

#pragma comment( lib, "ws2_32.lib" )

#define PORT 2046
#define MAXDATASIZE 100

void main( void )
{

int iClientSock;
struct sockaddr_in ServerAddr;

int numbytes;
char buf[ MAXDATASIZE ] = { 0 };

WSADATA WSAData;
if( WSAStartup( MAKEWORD( 1, 1 ), &WSAData ) )
{
printf( "initializationing error!\n" );
WSACleanup( );
exit( 0 );
}

if( ( iClientSock = socket( AF_INET, SOCK_DGRAM, 0 ) ) == -1 )
{
printf( "创建套接字失败!\n" );
WSACleanup( );
exit( 0 );
}

ServerAddr.sin_family = AF_INET;
ServerAddr.sin_port = htons( PORT );
ServerAddr.sin_addr.s_addr = inet_addr( "192.168.2.194" );//记得换IP
memset( &( ServerAddr.sin_zero ), 0, sizeof( ServerAddr.sin_zero ) );

numbytes = sendto( iClientSock, buf, strlen( buf ), 0, ( struct sockaddr * ) & ServerAddr, sizeof( struct sockaddr ) );
if( numbytes == -1 )
{
printf( "sendto调用失败!\n" );
WSACleanup( );
exit( 0 );
}

printf( "sent %d bytes to %s\n", numbytes, inet_ntoa( ServerAddr.sin_addr ) );

closesocket( iClientSock );
WSACleanup( );
}

8. 我想学习linux下的网络编程。

分别些一个客户端和服务端程序， 客户端和服务器端通过socket连接上后， 客户端接收用户输入，然后把用户输入发送到服务器端，服务器端再把这些信息打印/存盘。当用户输入某个特定单词（比如quit)，客户端结束与服务端的连结。

通过这个简单的程序，你就掌握了最基本的网络编程了。 :)

9. linux网络编程中如何实现服务器端多个read（）和客户端write( )

TCP通信的模式如下图，比较固定，对着图编代码就可以了：

因为客户端没有指定IP地址和端口，所以其IP和端口都是内核随机分配的。

10. 网络编程Linux如何实现客户端回射

这个可以用python写个程序，让服务器端一直监听某个端口，比如监听在9527端口上，然后用客户端去访问指定的ip+端口，就能连接到服务器上