Server端:

#include<stdio.h>
#include<stdlib.h>
#include<string.h>
#include<unistd.h>
#include<errno.h>
#include<pthread.h>
#include<ctype.h>
#include<sys/socket.h>
#include<arpa/inet.h>

#define SERV_PORT 9527

void sys_err(const char *str)
{
    perror(str);
    exit(
 
1);
}

int main(int argc,char *argv[])
{
    int lfd = 0,cfd = 0;
    int ret,i;
    char buf[BUFSIZ],client_IP[BUFSIZ];

    struct sockaddr_in serv_addr,clit_addr;
    socklen_t clit_addr_len;

    serv_addr.sin_family = AF_INET;
    serv_addr.sin_port = htons(SERV_PORT);
    serv_addr.sin_addr.s_addr 
 
= htonl(INADDR_ANY);


    lfd = socket(AF_INET,SOCK_STREAM,0);
    if(lfd==-1){
        sys_err("socket error");
    }

    bind(lfd,(struct sockaddr *)&serv_addr,sizeof(serv_addr));

    listen(lfd,128);

    clit_addr_len = sizeof(clit_addr);

    cfd = accept(lfd,(struct sockaddr *)&clit_addr,&clit_addr_len);
    
 
if(cfd==-1){
        sys_err("accept error");
    }
    printf("client ip:%s port:%d\n",
            inet_ntop(AF_INET, &clit_addr.sin_addr.s_addr,client_IP,sizeof(client_IP)),
            ntohs(clit_addr.sin_port));

    while(1){
        ret = read(cfd,buf,sizeof(buf));
        write(STDOUT_FILENO,buf,ret);

        for(i=0;i<ret;i++)
            buf[i]=toupper(buf[i]);

        write(cfd,buf,ret);
    }
    close(lfd);
    close(cfd);
    return 0;
}

Client端：

#include<stdio.h>
#include<stdlib.h>
#include<string.h>
#include<unistd.h>
#include<arpa/inet.h>
#include<sys/socket.h>

#define SERV_PORT 9527

void sys_err(const char *str)
{
    perror(str);
    exit(1);
}

int main(int argc,char *argv[])
{
    int cfd;
    int conter=10;
    char buf[BUFSIZ];
        
    struct sockaddr_in serv_addr;
    serv_addr.sin_family = AF_INET;
    serv_addr.sin_port = htons(SERV_PORT);

    inet_pton(AF_INET,"127.0.0.1",&serv_addr.sin_addr.s_addr);

    cfd = socket(AF_INET,SOCK_STREAM,0);
    if(cfd==-1)
        sys_err("socket error");

    int ret = connect(cfd,(struct sockaddr *)&serv_addr,sizeof(serv_addr));
    if(ret!=0)
        sys_err("connect error");

    while(conter--)
    {
        write(cfd,"hello\n",6);
        ret = read(cfd,buf,sizeof(buf));
        write(STDOUT_FILENO,buf,ret);
        sleep(1);
    }
    close(cfd);

    return 0;
}

執行的時候，開2個視窗，一個視窗跑server端，./server即可，另一個跑client端，./client即可。注意要先編譯。