C语言简单的客户端和服务端程序

服务端程序

#include<stdio.h>
#include<string.h>
#include<stdlib.h>
#include<unistd.h>
#include<sys/types.h>
#include<sys/socket.h>    
#include<netinet/in.h>
#include<arpa/inet.h>
#define PORT 1234
#define BACKLOG 1
main()
{
int listenfd,connectfd;
struct sockaddr_in server;
struct sockaddr_in client;
int sin_size;
if((listenfd = socket(AF_INET,SOCK_STREAM,0)) == -1){
  perror("Creating socket failed.");
  exit(1);
}
  int  opt = SO_REUSEADDR;
setsockopt(listenfd , SOL_SOCKET, SO_REUSEADDR , &opt, sizeof(opt));
bzero(&server,sizeof(server));
server.sin_family=AF_INET;
server.sin_port=htons(PORT);
server.sin_addr.s_addr = htonl(INADDR_ANY);
if(bind(listenfd,(struct sockaddr *)&server,sizeof(struct sockaddr)) == -1){
perror("Bind error.");
exit(1);
}

if(listen(listenfd ,BACKLOG) == -1){
perror("listen() error \n");
exit(1);
}
sin_size = sizeof(struct sockaddr_in);
if((connectfd = accept(listenfd,(struct sockaddr *) &client, &sin_size)) == -1){
perror("accept() error \n");
exit(1);
}
printf("You got a connection from %s \n" ,inet_ntoa(client.sin_addr));
send(connectfd,"welcome to my server.\n",22,0);
close(connectfd);
close(listenfd);
}

客户端程序

#include<stdio.h>
#include<stdlib.h>
#include<strings.h>
#include<sys/types.h>
#include<sys/socket.h>
#include<netinet/in.h>
#include<netdb.h>
#define PORT 1234
#define MAXDATASIZE 100
int main(int argc,char *argv[])
{
int fd,numbytes;
char buf[MAXDATASIZE];
struct hostent *he;
struct sockaddr_in server;
if(argc !=2){
printf("Usage: %s <IP Address> \n",argv[0]);
exit(1);
}


if((he = gethostbyname(argv[1]))==NULL){
/*调用gethostbyname()函数*/
printf("gethostbyname()  error \n");
exit(1);
}

if((fd=socket(AF_INET,SOCK_STREAM,0)) == -1){
/*调用socket（）函数*/
printf("socket() error \n");
exit(1);
}
bzero(&server,sizeof(server));
server.sin_family=AF_INET;
server.sin_port=htons(PORT);
server.sin_addr=*((struct in_addr *)he -> h_addr);
if(connect(fd,(struct sockaddr *)&server,sizeof(struct sockaddr))==-1){/*调用connect()函数*/
printf("connect() error \n");
exit(1);
}
if((numbytes=recv(fd,buf,MAXDATASIZE,0))== -1){
/*调用recv（）函数*/
printf("recv() error\n");
exit(1);
}
buf[numbytes] = '\0';
printf("Server Message:%s \n",buf);/*显示服务器端的欢迎信息*/
close(fd);
}