我在自己的电脑上，装了一个虚拟机，算上我的真实系统一共两个IP地址，进行IP地址扫描的时候可以全都扫描出来，

但是今天我把电脑连入朋友的局域网里时，只能扫描到自己的IP地址，其他的扫描到了，但是没有输入其他电脑的IP，MAC，主机名，不知道为什么？？？

可以执行的文件

#include "stdio.h"
#include "stdlib.h"
#include "winsock2.h"
#include "Iphlpapi.h"
#include "time.h"

#pragma comment    (lib,"ws2_32.lib")
#pragma comment    (lib,"iphlpapi.lib")

char *net_id;
char check_ip[256][10];
SOCKET    sock;
WSADATA    wsa;
HOSTENT *host;
IPAddr now_ip;
clock_t    start_time,end_time;
float costtime;
int    Threadnum = 0;
int    hostnum = 0;

//  自定义函数原形声明
void usage(char *);

void Display_Face();

void Display_Welcome();

void check_input(int argc,char**argv);  

void check_socket();

void Get_Mac(int );

void Get_Host_Name();

DWORD WINAPI scan_lan(LPVOID lp);


int main(int argc,char **argv)
{
    if ( argc < 2)
    {
        usage(argv[0]);
    }
    check_input(argc,argv);

    check_socket();

    system("cls");

    Display_Welcome();

    Display_Face();

    start_time = clock();

    for ( int i = 1; i <= 254; i++)
    {    
        CreateThread(NULL,0,scan_lan,&i,0,NULL);
        Threadnum++;
        Sleep(10);
    }

    end_time = clock();

    costtime = (float)(end_time - start_time) / CLOCKS_PER_SEC;
    printf("%26s\n本次扫描用时 %.4f Seconds\n"," ",costtime);
    printf("\n局域网内共有%3d个主机存活\n",hostnum);
    Sleep(100);
    return 0;
}


void check_input(int argc,char **argv)  //检测输入数据
{
    net_id = &argv[1][0];
}

void check_socket()   //启动socket库
{
    if ( WSAStartup( MAKEWORD(2,0),&wsa) != 0)
    {
        printf("Socket load fail...\n");

        return ;
    }

    sock = socket(AF_INET,SOCK_STREAM,0);
    if (sock == INVALID_SOCKET)
    {
        printf("Socket build faill...\n");

        return ;
    }
}

void Get_Mac(int host_id)  //获取主机MAC
{

    ULONG    mac[2];
    ULONG    mac_len;

    memset(mac,0xff,sizeof(mac));
    mac_len = 6;

    sprintf(check_ip[host_id],"%s.%d",net_id,host_id);

    printf("Scaning ip:%s\r",check_ip[host_id]);
    now_ip = inet_addr(check_ip[host_id]);

    DWORD hr = SendARP( now_ip, 0, mac, &mac_len);

    if (hr ==NO_ERROR)
    {
        hostnum ++;

        unsigned char * mac_addr=(unsigned char*)mac;

        Get_Host_Name();   //如果主机存活，获取主机名
        
        printf("%10s\t\t%10s.%d\t\t%02X-%02X-%02X-%02X-%02X-%02X\n",host->h_name ,net_id,host_id,mac_addr[0],mac_addr[1],mac_addr[2],mac_addr[3],mac_addr[4],mac_addr[5]);
    }
    InterlockedExchangeAdd((long *)&Threadnum,-1);

}

void Get_Host_Name()  //根据IP地址，获取对应的主机名
{
    host = gethostbyaddr( (char *)&now_ip,4,AF_INET);
    /*
    if (host == NULL)  //如果返回NULL，则不存在，这里应该可以去掉这个判断，因为主调函数Get_Mac()已经判断了主机存活
    {
        InterlockedExchangeAdd((long *)&Threadnum,-1);
        return ;
    }
    */
}

DWORD WINAPI scan_lan(LPVOID lp) //扫描线程函数
{
    int host_id = *(DWORD*)lp;

    Get_Mac(host_id);

    InterlockedExchangeAdd((long *)&Threadnum,-1);

    return 0;

}

void usage(char *filename)
{
    printf("\nusage : %s Network_Address\n",filename);
    printf("\nIf your ip address is: 192.168.1.1 \n\nPlease input:");
    printf("\t%s 192.168.1\n",filename);
    exit(0);
}

void Display_Welcome()
{
    printf("\n");
    printf("  ===========================================================================\n");
    printf("  =                                                                         =\n");
    printf("  =                  Welcome  to  using  ip  scaner                         =\n");
    printf("  =                      Programing By okhelper                             =\n");
    printf("  =                           QQ:274002432                                  =\n");
    printf("  =                             2008.5.8                                    =\n");
    printf("  =                                                                         =\n");
    printf("  ===========================================================================\n");
}

void Display_Face()
{
    printf("\n\t\t%2s局  域  网  内  存  活  主  机  列  表\n"," ");
    printf(" -----------------------------------------------------------------------------\n");
    printf("\n  计 算 机 名\t\tI P 地 址\t\tM A C 地 址\n\n");
}