server.c

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

int main(int argc, char *argv[])
{
        int sockfd,new_fd;
        struct sockaddr_in server_addr;
        struct sockaddr_in client_addr;
        int sin_size,portnumber;
        char hello[1000]="Hello! Are You Fine?\n";

        if(argc!=2)
        {
                fprintf(stderr,"Usage:%s portnumber\a\n",argv[0]);
                exit(1);
        }

        if((portnumber=atoi(argv[1]))<0)
        {
                fprintf(stderr,"Usage:%s portnumber\a\n",argv[0]);
                exit(1);
        }

        /* server端開始建立socket描写叙述符 */
        if((sockfd=socket(AF_INET,SOCK_STREAM,0))==-1)
        {
                fprintf(stderr,"Socket error:%s\n\a",strerror(errno));
                exit(1);
        }

        /* server端填充 sockaddr结构  */
        bzero(&server_addr,sizeof(struct sockaddr_in));
        server_addr.sin_family=AF_INET;
        server_addr.sin_addr.s_addr=htonl(INADDR_ANY);
        server_addr.sin_port=htons(portnumber);

        /* 捆绑sockfd描写叙述符  */
        if(bind(sockfd,(struct sockaddr *)(&server_addr),sizeof(struct sockaddr))==-1)
        {
                fprintf(stderr,"Bind error:%s\n\a",strerror(errno));
                exit(1);
        }

        /* 监听sockfd描写叙述符  */
        if(listen(sockfd,5)==-1)
        {
                fprintf(stderr,"Listen error:%s\n\a",strerror(errno));
                exit(1);
        }

        while(1)
        {
                /* server堵塞,直到客户程序建立连接  */
                sin_size=sizeof(struct sockaddr_in);
                if((new_fd=accept(sockfd,(struct sockaddr *)(&client_addr),&sin_size))==-1)
                {
                        fprintf(stderr,"Accept error:%s\n\a",strerror(errno));
                        exit(1);
                }

                fprintf(stderr,"Server get connection from %s\n",
                inet_ntoa(client_addr.sin_addr));

                fscanf(stdin,"%s",hello);
                if(write(new_fd,hello,strlen(hello))==-1)
                {
                        fprintf(stderr,"Write Error:%s\n",strerror(errno));
                        exit(1);
                }
                /* 这个通讯已经结束     */
                close(new_fd);
                /* 循环下一个     */
        }
        close(sockfd);
        exit(0);
}

client.c

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

int main(int argc, char *argv[])
{
        int sockfd;
        char buffer[1024];
        struct sockaddr_in server_addr;
        struct hostent *host;
        int portnumber,nbytes;

        if(argc!=3)
        {
                fprintf(stderr,"Usage:%s hostname portnumber\a\n",argv[0]);
                exit(1);
        }

        if((host=gethostbyname(argv[1]))==NULL)
        {
                fprintf(stderr,"Gethostname error\n");
                exit(1);
        }

        if((portnumber=atoi(argv[2]))<0)
        {
                fprintf(stderr,"Usage:%s hostname portnumber\a\n",argv[0]);
                exit(1);
        }

        /* 客户程序開始建立 sockfd描写叙述符  */
        if((sockfd=socket(AF_INET,SOCK_STREAM,0))==-1)
        {
                fprintf(stderr,"Socket Error:%s\a\n",strerror(errno));
                exit(1);
        }

        /* 客户程序填充服务端的资料       */
        bzero(&server_addr,sizeof(server_addr));
        server_addr.sin_family=AF_INET;
        server_addr.sin_port=htons(portnumber);
        server_addr.sin_addr=*((struct in_addr *)host->h_addr);

        /* 客户程序发起连接请求         */
        if(connect(sockfd,(struct sockaddr *)(&server_addr),sizeof(struct sockaddr))==-1)
        {
                fprintf(stderr,"Connect Error:%s\a\n",strerror(errno));
                exit(1);
        }

        /* 连接成功了           */
        if((nbytes=read(sockfd,buffer,1024))==-1)
        {
                fprintf(stderr,"Read Error:%s\n",strerror(errno));
                exit(1);
        }
        buffer[nbytes]='\0';
        printf("I have received:%s\n",buffer);
        /* 结束通讯     */
        close(sockfd);
        exit(0);
}

Makefile

all:server client
server:server.c
            gcc $^ -o $@
client:client.c
            gcc $^ -o $@