请优化这段代码，执行ioctl报错无效的参数：#include <stdio.h> #include <stdlib.h> #include <string.h> #include <unistd.h> #include <sys/socket.h> #include <sys/ioctl.h> #include <netinet/in.h> #include <net/if.h> #include <arpa/inet.h> #include <linux/route.h> int main() { int fd; struct rtentry route; struct sockaddr_in *addr; memset(&route, 0, sizeof(route)); route.rt_dst.sa_family = AF_INET; addr = (struct sockaddr_in *)&route.rt_gateway; addr->sin_family = AF_INET; fd = socket(AF_INET, SOCK_DGRAM, 0); if (ioctl(fd, SIOCRTMSG, &route) == -1) { perror("ioctl"); exit(1); } close(fd); printf("Gateway address: %s\n", inet_ntoa(addr->sin_addr)); return 0; }

这段代码的问题在于使用了已经过时的 SIOCRTMSG ioctl 命令，并且没有对错误进行恰当的处理。可以使用更现代化的方法，如使用 netlink socket 来获取网关地址。以下是更新后的代码： ```c++ #include <stdio.h> #include <stdlib.h> #include <string.h> #include <unistd.h> #include <sys/socket.h> #include <linux/netlink.h> #include <linux/rtnetlink.h> #include <arpa/inet.h> #define MAX_PAYLOAD 1024 int main() { int sockfd; struct sockaddr_nl sa; struct nlmsghdr *nlh; char buffer[MAX_PAYLOAD]; struct rtmsg *rtm; struct rtattr *rta; int len; memset(&sa, 0, sizeof(sa)); sa.nl_family = AF_NETLINK; nlh = (struct nlmsghdr *)buffer; rtm = (struct rtmsg *)NLMSG_DATA(nlh); nlh->nlmsg_len = NLMSG_LENGTH(sizeof(struct rtmsg)); nlh->nlmsg_type = RTM_GETROUTE; nlh->nlmsg_flags = NLM_F_REQUEST | NLM_F_DUMP; sockfd = socket(AF_NETLINK, SOCK_RAW, NETLINK_ROUTE); if (sockfd == -1) { perror("socket"); exit(1); } if (bind(sockfd, (struct sockaddr *)&sa, sizeof(sa)) == -1) { perror("bind"); exit(1); } if (send(sockfd, nlh, nlh->nlmsg_len, 0) == -1) { perror("send"); exit(1); } while ((len = recv(sockfd, buffer, MAX_PAYLOAD, 0)) > 0) { for (nlh = (struct nlmsghdr *)buffer; NLMSG_OK(nlh, len); nlh = NLMSG_NEXT(nlh, len)) { if (nlh->nlmsg_type == NLMSG_DONE) { break; } else if (nlh->nlmsg_type == NLMSG_ERROR) { perror("recv"); exit(1); } else if (nlh->nlmsg_type == RTM_NEWROUTE) { rtm = (struct rtmsg *)NLMSG_DATA(nlh); if (rtm->rtm_table != RT_TABLE_MAIN) { continue; } rta = (struct rtattr *)RTM_RTA(rtm); len = RTM_PAYLOAD(nlh); for (; RTA_OK(rta, len); rta = RTA_NEXT(rta, len)) { if (rta->rta_type == RTA_GATEWAY) { struct in_addr *addr = (struct in_addr *)RTA_DATA(rta); printf("Gateway address: %s\n", inet_ntoa(*addr)); close(sockfd); return 0; } } } } } close(sockfd); return 0; } ``` 这个程序使用 netlink socket 发送 RTM_GETROUTE 请求来获取路由表，并遍历路由表中的每个条目，找到目标路由条目，并从中提取出网关地址。此方法可以避免使用已经过时的 ioctl 命令，并且可以正确地处理错误。