如果我用了网络执法官（是会自动发包的吧）的话，可以捕获ARP响应。没有使用的话，不会响应！所以我认为是没有发送数据包，或者数据包错误，其他主机解析不了。弄了好久了，还是不行，请大家帮帮忙，谢谢了！
#include "pcap.h"
#pragma comment(lib,"wpcap")
#pragma comment(lib,"ws2_32")
//=========数据包结构申明========================
typedef struct IP_Address //32位的IP地址
{
u_char byte1;
u_char byte2;
u_char byte3;
u_char byte4;

}ip_address;

typedef struct Hard_Mac //48位的MAC地址
{
u_char byte1;
u_char byte2;
u_char byte3;
u_char byte4;
u_char byte5;
u_char byte6;
}Hard_Mac;

/* Ethernet header */
typedef struct Ethernet_Header //112位 48位SMac+48位SMac+16位协议类型 以太网头
{
Hard_Mac DMac; //(1)48位目MAC地址
Hard_Mac SMac; //(2)48位源MAC地址
WORD PType; //(3)16位协议类型
}Ethernet_Header;
typedef struct ARP_Header //定义ARP首部
{
Ethernet_Header FrameHeader;//帧头
WORD HardWare; //(4)16位网卡硬件类型
WORD PType3; //(5)16位协议类型
u_char HLeng; //(6)8位硬件地址长度
u_char PLeng; //(7)16位协议地址长度
WORD Oper; //(8)16位操作选项
Hard_Mac SMac3; //(9)48位源MAC地址
ip_address Saddr; //(10)32位源IP地址
Hard_Mac DMac3; //(11)48位目标MAC地址
ip_address Daddr; //(12)32位目标IP地址
BYTE padding[18]; //填充0
}ARP_Header;

//=====================================================================
//填充APR数据包
//======================================================================
ARP_Header filtpacket()
{
ARP_Header ARPH; //发送的ARP包结构
//先初始化三层ARP的MAC地址
ARPH.DMac3.byte1 = 0; ARPH.DMac3.byte2 = 0; ARPH.DMac3.byte3 = 0;
ARPH.DMac3.byte4 = 0; ARPH.DMac3.byte5 = 0; ARPH.DMac3.byte6 = 0; //目标MAC地址

ARPH.SMac3.byte1 = 0x00; ARPH.SMac3.byte2 = 0x11; ARPH.SMac3.byte3 = 0xD8;
ARPH.SMac3.byte4 = 0x71; ARPH.SMac3.byte5 = 0x66; ARPH.SMac3.byte6 = 0x09; //源MAC地址

ARPH.FrameHeader.SMac.byte1 = 0x00; ARPH.FrameHeader.SMac.byte2 =0x11; ARPH.FrameHeader.SMac.byte3=0xD8;
ARPH.FrameHeader.SMac.byte4 = 0x71; ARPH.FrameHeader.SMac.byte5 = 0x66; ARPH.FrameHeader.SMac.byte6=0x09; //源MAC地址

ARPH.FrameHeader.DMac.byte1 = 0xFF; ARPH.FrameHeader.DMac.byte2 = 0xFF; ARPH.FrameHeader.DMac.byte3 = 0xFF;
ARPH.FrameHeader.DMac.byte4 = 0xFF; ARPH.FrameHeader.DMac.byte5 = 0xFF; ARPH.FrameHeader.DMac.byte6 = 0xFF; //目标MAC地址

ARPH.FrameHeader.PType = htons(0x0806);//协议类型为ARP

ARPH.HardWare =htons(0x0001);//10M Ethernet

ARPH.PType3 =htons(0x0800);//协议类型为IP

ARPH.HLeng = 6 ; //硬件地址长度

ARPH.PLeng = 4 ; //IP地址长度

ARPH.Oper = htons(0x0001) ; //请求操作

ARPH.Daddr.byte1=172;ARPH.Daddr.byte2=18;ARPH.Daddr.byte3=19;ARPH.Daddr.byte4=20; //目标IP地址

ARPH.Saddr.byte1=172;ARPH.Saddr.byte2=18;ARPH.Saddr.byte3=19;ARPH.Saddr.byte4=116; //源IP地址
int i;
for(i=0;i<18;i++)
{
ARPH.padding[i]=0;
}
return ARPH;
};
//==========================================================
//发送数据包
//==========================================================
void SendPacket(pcap_t *adhandle,ARP_Header ARPH)
{
const u_char *Buff;
Buff = &ARPH.FrameHeader.DMac.byte1 ; //结构首地址传入Buff

if(pcap_sendpacket(adhandle, // Adapter
Buff, // buffer with the packet
sizeof(Buff)// size
)!=0)
{
printf("发送数据包失败\n");
}
else
printf("发送数据包成功！\n");
}
//=======================================================
//解析数据包
//=======================================================
void packet_handler(u_char *param, const struct pcap_pkthdr *header, const u_char *pkt_data)
{
ARP_Header *ah;

ah = (ARP_Header *) (pkt_data);

if(ah->FrameHeader.PType==1544&&
ah->Oper==512&&
ah->Daddr.byte1==172&&
ah->Daddr.byte2==18&&
ah->Daddr.byte3==19&&
ah->Daddr.byte4==116
&& ah->Saddr.byte1==172&&
ah->Saddr.byte2==18&&
ah->Saddr.byte3==19&&
ah->Saddr.byte4==20
)
{
/*输出源IP地址，目的IP地址*/
printf("\n%d.%d.%d.%d-> %d.%d.%d.%d\n",
ah->Saddr.byte1,
ah->Saddr.byte2,
ah->Saddr.byte3,
ah->Saddr.byte4,
ah->Daddr.byte1,
ah->Daddr.byte2,
ah->Daddr.byte3,
ah->Daddr.byte4);
/*输出目的地址，输出源地址，输入协议类型*/
Hard_Mac SMAC,DMAC;
Ethernet_Header *eh;
eh=(Ethernet_Header*)pkt_data;
SMAC=eh->SMac;
printf("源地址 %.2x--%.2x--%.2x--%.2x--%.2x--%.2x\n"
,SMAC.byte1,SMAC.byte2,SMAC.byte3,SMAC.byte4,SMAC.byte5,SMAC.byte6);
DMAC=eh->DMac;
printf("目的地址 %.2x--%.2x--%.2x--%.2x--%.2x--%.2x\n"
,DMAC.byte1,DMAC.byte2,DMAC.byte3,DMAC.byte4,DMAC.byte5,DMAC.byte6);
printf("帧协议 %.4x\n",ntohs(eh->PType));
printf("硬件类型%.4x\n",ntohs(ah->HardWare));
printf("协议类型%.4x\n",ntohs(ah->PType3));
printf("操作类型%.4x\n",ntohs(ah->Oper));
printf("数据内容%x\n",ah->padding);
printf("\n\n==============================================================\n");
}
}
int main()
{
//打开网卡
pcap_if_t *alldevs;
pcap_if_t *d;
int inum;
int i=0;
pcap_t *adhandle;
char errbuf[PCAP_ERRBUF_SIZE];
char packet_filter[] ="arp";
/* Retrieve the device list */
if (pcap_findalldevs(&alldevs, errbuf) == -1)
{
fprintf(stderr,"Error in pcap_findalldevs: %s\n", errbuf);
exit(1);
}

/* Print the list */
for(d=alldevs; d; d=d->next)
{
printf("%d. %s", ++i, d->name);
if (d->description)
printf(" (%s)\n", d->description);
else
printf(" (No description available)\n");
}

if(i==0)
{
printf("\nNo interfaces found! Make sure WinPcap is installed.\n");
return -1;
}

printf("Enter the interface number (1-%d):",i);
scanf("%d", &inum);

if(inum < 1 || inum > i)
{
printf("\nInterface number out of range.\n");
/* Free the device list */
pcap_freealldevs(alldevs);
return -1;
}

/* Jump to the selected adapter */
for(d=alldevs, i=0; i< inum-1 ;d=d->next, i++);

/* Open the adapter */
if ( (adhandle= pcap_open_live(d->name, // name of the device
65536, // portion of the packet to capture.
// 65536 grants that the whole packet will be captured on all the MACs.
1, // promiscuous mode
1000, // read timeout
errbuf // error buffer
) ) == NULL)
{
fprintf(stderr,"\nUnable to open the adapter. %s is not supported by WinPcap\n");
/* Free the device list */
pcap_freealldevs(alldevs);
return -1;
}


/* At this point, we don't need any more the device list. Free it */
pcap_freealldevs(alldevs);

SendPacket(adhandle,filtpacket());//发送数据包

pcap_loop(adhandle, 0, packet_handler, NULL); //捕获数据包

return 0;

}