C++ 简易scoket Server

//     #include <stdio.h>  #include <stdlib.h>  #include <unistd.h>  #include <string.h>  #include <sys/types.h>  #include <sys/socket.h>  #include <netinet/in.h>  #include <arpa/inet.h>  #include <errno.h>  #include <sys/select.h>        #define MAXUSERS 5  #define BUFFER_SIZE 64  #define FD_LIMIT 65535     int USERS[MAXUSERS];  int user_count = 0;        void showclient()  {      int i;      printf("user_count: %d\n", user_count);      for (i = 0; i < MAXUSERS; i++) {          printf("[%d]:%d  ", i, USERS[i]);      }      printf("\n\n");  }     int main(int argc, const char * argv[])  {             struct sockaddr_in server_addr;      struct sockaddr_in client_addr;             socklen_t client_addrlength = sizeof(client_addr);                    bzero(&server_addr, sizeof(server_addr));      server_addr.sin_family = AF_INET;      server_addr.sin_port = htons(33333);      server_addr.sin_addr.s_addr = htonl(INADDR_ANY);             //创建      int sock_fd = socket( PF_INET, SOCK_STREAM, 0 );      if (sock_fd<0) {          printf("socket error:%d",errno);          close(sock_fd);          exit(1);      }                    int yes = 1;      if (setsockopt(sock_fd, SOL_SOCKET, SO_REUSEADDR, &yes, sizeof(int)) == -1) {          perror("setsockopt");          exit(1);      }                    int sret;             //绑定      sret = bind( sock_fd, (struct sockaddr *)&server_addr, sizeof(server_addr) );      if (sret<0) {          printf("bind error:%d",errno);          close(sock_fd);          exit(2);      }             //监听      sret = listen(sock_fd, MAXUSERS);      if (sret<0) {          printf("listen error:%d",errno);          close(sock_fd);          exit(3);      }      printf("start ok, listen port:%d\n", ntohs(server_addr.sin_port));             char buf[1024];      int maxsock = sock_fd;                    fd_set read_fds;        //可读      ssize_t ret;             while (1) {                     FD_ZERO(&read_fds);          FD_SET(sock_fd, &read_fds);                     //需要监听的集合          for (int i =0; i<user_count; i++) {              if (USERS[i] != 0) {                  FD_SET(USERS[i], &read_fds);              }          }                     //注册监听事件          ret = select(maxsock+1, &read_fds, NULL, NULL, NULL);          if (ret<0) {              printf("select error\n");              continue;          }else if (ret==0){              printf("select timeout\n");              continue;          }                     //读取客户端发来的数据          for (int i =0; i<user_count; i++) {              if (FD_ISSET(USERS[i], &read_fds)) {                  ret = recv(USERS[i], buf, sizeof(buf), 0);                  printf("client[%d] send:%s\n", i, buf);              }          }                     //处理新用户链接          if (FD_ISSET(sock_fd, &read_fds)) {              printf("new client\n");              int new_fd = accept(sock_fd, (struct sockaddr *)&client_addr, &client_addrlength);              if (new_fd<0) {                  printf("accept error\n");                  close(new_fd);                  continue;              }                             USERS[user_count] = new_fd;              printf("new connection client[%d] %s:%d\n", user_count,                     inet_ntoa(client_addr.sin_addr), ntohs(client_addr.sin_port));              user_count++;              if (new_fd > maxsock){                  maxsock = new_fd;              }          }                     showclient();      }                                  close(sock_fd);      return 0;  }