使用套接字socket实现服务器和客户端之间的TCP通信。

流程如下：

实现代码：

/* server.c */
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
#include <arpa/inet.h>
#include <sys/types.h>          /* See NOTES */
#include <sys/socket.h>
#include <errno.h>
#include <ctype.h>#define SERV_PORT 9527void sys_err(const char *str)
{perror(str);exit(1);
}int main(int argc, char *argv[])
{struct sockaddr_in serv_addr, client_addr;socklen_t client_addr_len;char buf[BUFSIZ], client_IP[1024];//1. 创建监听套接字int lfd = socket(AF_INET,  //IPV4SOCK_STREAM, 0);if(lfd == -1) //check RETURN VALUE{sys_err("socket error");}//2. 绑定本地的IP地址和端口号serv_addr.sin_family = AF_INET;serv_addr.sin_port = htons(SERV_PORT);serv_addr.sin_addr.s_addr = htonl(INADDR_ANY);int ret = bind(lfd,  (struct sockaddr *)&serv_addr, sizeof(serv_addr));if(ret == -1){sys_err("bind error");}//3. 设置监听int ret_listen = listen(lfd, 128);if(ret_listen == -1){sys_err("listen error");}//4. 阻塞等待，连接的到达，连接成功后返回通信用的套接字client_addr_len = sizeof(client_addr);int cfd = accept(lfd, (struct sockaddr*)&client_addr, &client_addr_len);if(cfd == -1){sys_err("accept error");}printf("client ip is %s, port is %d\n",inet_ntop(AF_INET, &client_addr.sin_addr.s_addr, client_IP, sizeof(client_IP)),ntohs(client_addr.sin_port));//5. 开始通信while(1){ssize_t ret_acc = read(cfd, buf, sizeof(buf));write(STDOUT_FILENO, buf, ret_acc);for(int i = 0; i < ret_acc; i++){buf[i] = toupper(buf[i]);}write(cfd, buf, ret_acc);}close(lfd);close(cfd);return 0;
}

/* client.c */
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
#include <arpa/inet.h>
#include <sys/types.h>          /* See NOTES */
#include <sys/socket.h>
#include <errno.h>
#include <ctype.h>#define SERV_PORT 9527void sys_err(const char *str)
{perror(str);exit(1);
}int main(int argc, char *argv[])
{int cfd;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);char buf[BUFSIZ];int cnt = 10;//1. 创建监听套接字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(cnt--){write(cfd, "hello\n", 6);ret = read(cfd, buf, sizeof(buf));write(STDERR_FILENO, buf, ret);sleep(1);}close(cfd);return 0;
}

实验现象
客户端向服务器发送10次hello，接收到服务器发来的10次大写HELLO；服务器首先打印IP地址和端口号，随后打印收到的10次由客户端传来的hello。