查看局域网内所有在线的ip 升级（可靠）

/*

  程序可以根据需要做适当的修改

  可以先对照看看我的第一个版本，使用-t 最好设置成5秒到10秒左右。否则将可能检测不到下面的第一种情况。

  1.如果局域网内一台电脑使用了应用层防火墙比如天网之类，会connect超时。对方在线

  2.connect success 连接成功，对方在线

  3.connect refused 拒绝连接，对方在线

  4.no route 连续发送5个arp请求（没有结果）和一个dns查询后（返回nxdomain），内核产生no route的错误。对方不在线

  林汉杰 2008-7-16

*/

 

 

#include "stdio.h"
#include "stdlib.h"
#include "string.h"
 
#include "unistd.h"
#include "sys/types.h"
#include "sys/time.h"
#include "sys/socket.h"
#include "arpa/inet.h"
#include "netinet/in.h"
#include "netdb.h"
#include "fcntl.h"
#include "errno.h"
 
 
void usage() {
        printf("use format:\n\t-s startip\n\t-e endip\n\t-t connect_timeout\n\t-p port\n");
        exit(-1);
}
int main(int argc, char** argv) {
 
 
        int start_ip = 1;
        int end_ip = 254;
        int time_connect = 10;
        int port = 8888;
 
        int opt;
        while((opt = getopt(argc, argv, "s:e:t:p:")) != -1) {
                switch(opt) {
                        case 's':start_ip = atoi(optarg);break;
                        case 'e':end_ip   = atoi(optarg);break;
                        case 't':time_connect = atoi(optarg);break;
                        case 'p':port = atoi(optarg);break;
                        case '?':usage();break;
                }
        }
 
        printf("-----------------------------------------------------------------------------------------------------\n");
        printf("\t scan will use 192.168.1.%d -> 192.168.1.%d with connect timeout %d in port %d\n", start_ip, end_ip, time_connect, port);
        printf("-----------------------------------------------------------------------------------------------------\n");
        struct timeval timeout;
        fd_set wset;
        fd_set rset;
        char straddr[100];
        for(int i=start_ip; i 
                int sockfd = socket(AF_INET, SOCK_STREAM, 0);
                if(sockfd == -1)perror("socket()");
 
                sprintf(straddr, "192.168.1.%d\0", i);
                fprintf(stderr, "scan %s\t", straddr);
 
                struct sockaddr_in server_addr;
                server_addr.sin_family = AF_INET;
                if(inet_pton(AF_INET, straddr, &(server_addr.sin_addr)) != 1)perror("inet_pton()");
                server_addr.sin_port = htons(port);
 
                int flags;
                if((flags = fcntl(sockfd, F_GETFL, 0)) < 0)perror("fcntl()");
                if(fcntl(sockfd, F_SETFL, flags | O_NONBLOCK)< 0)perror("fcntl()");
                int result = connect(sockfd, (struct sockaddr*)(&server_addr), sizeof(server_addr));
                if(result == -1) {
                        if(errno == EINPROGRESS) {
                                timeout.tv_sec  = 10;
                                timeout.tv_usec = 0;
                                if(time_connect >= 100) {
                                        timeout.tv_sec  = 0;
                                        timeout.tv_usec = time_connect;
                                } else if(time_connect > 0) {
                                        timeout.tv_sec  = time_connect;
                                        timeout.tv_usec = 0;
                                }
                                FD_ZERO(&wset);
                                FD_SET(sockfd, &wset);
                                rset = wset;
                                int n = select(sockfd+1, &rset, &wset, 0, &timeout);
                                if(n == -1 && errno!= EINTR) {
                                        perror("select() error");
                                } else if(n > 0) {
 
                                        int optval;
                                        int optlen = 4;
                                        if(getsockopt(sockfd, SOL_SOCKET, SO_ERROR, (void*)&optval, (socklen_t*)&optlen) < 0)perror("getsockopt()");
                                        if(optval == 0) {
                                                fprintf(stderr, "success select\n");
                                        } else {
                                                fprintf(stderr, "failed select %d:%s\n", optval, strerror(optval));
                                        }
                                } else if(n == 0) {
                                        fprintf(stderr, "connect timeout\n");
                                }
                        } else {
                                close(sockfd);
                                perror("connect()");
                        }
                } else {
                        printf("connect() success\n");
                        close(sockfd);
                        continue;
                }
                close(sockfd);
        }
        return 0;
 
}