#include <stdio.h>
#include <netinet/in.h>
#include <sys/socket.h>
#include <arpa/inet.h>

#define IPADDRESS   "0.0.0.0"
#define PORT        8787
#define LISTENQ     5
#define MAXLINE     1024

int main() {
      // int socket (int domain, int type, int protocol)
      int listenfd = socket(AF_INET, SOCK_STREAM, 0);

      if(listenfd == -1){
            printf("socket error");
            return -1;
      }

      // int bind (int fd, sockaddr * addr, socklen_t len)
      struct sockaddr_in servaddr;
      
      servaddr.sin_family = AF_INET;
      servaddr.sin_port = htons(PORT);
      // servaddr.sin_addr.s_addr = htonl(INADDR_ANY);
      inet_pton(AF_INET, IPADDRESS, &servaddr.sin_addr);

      if (bind(listenfd, (struct sockaddr*)&servaddr, sizeof(servaddr)) == -1) {
            printf("bind error");
            return -1;
      }

      // int listen (int socketfd, int backlog)
      if (listen(listenfd,LISTENQ) == -1) {
            printf("listen error");
            return -1;
      }

      // int accept(int listensockfd, struct sockaddr *cliaddr, socklen_t *addrlen)
      struct sockaddr_in cliaddr;
      socklen_t cliaddrlen = sizeof(cliaddr);
      int connfd;

      if ((connfd = accept(listenfd, (struct sockaddr*)&cliaddr, &cliaddrlen)) == -1) {
            perror("accept error:");
            return 1;
      }else{
            printf("start up: sleep 3s");
            sleep(3);
      }

      printf("accept a new client: %s:%d\n", inet_ntoa(cliaddr.sin_addr), cliaddr.sin_port);

      // ssize_t read (int socketfd, void *buffer, size_t size)
      // ssize_t write (int socketfd, const void *buffer, size_t size)
      int n;
      char buf[MAXLINE];

      for (; ;) {
            n = read(connfd,buf,MAXLINE);
            if (n==0) {
                  break;
            }
            // printf("read msg is: ");
            // write(STDOUT_FILENO,buf,n);
            //向客户端发送buf
            write(connfd,buf,n);
      }

      close(connfd);
      close(listenfd);
}

• 若没加入 <arpa/inet.h>， 执行 printf("accept a new client: %s:%d\n", inet_ntoa(cliaddr.sin_addr), cliaddr.sin_port); 这行语句时，会报Segmentation fault (core dumped)的错误