Implement ARP packet sending in C language in linux

ARP packets can be sent at will. The source code is as follows:
# Include <netdb. h>
# Include <sys/socket. h>
# Include <sys/types. h>
# Include <stdio. h>
# Include <errno. h>
# Include <sys/ioctl. h>
# Include <net/if. h>
# Include <signal. h>
# Include <netinet/ip. h>
# Include <netinet/in. h>
# Include <string. h>
# Include <arpa/inet. h>
# Include <netinet/ip_icmp.h>
# Include <linux/if_ether.h>
# Define ETH_HW_ADDR_LEN 6
# Define IP_ADDR_LEN 4
# Define ARP_FRAME_TYPE 0x0806
# Define ETHER_HW_TYPE 1
# Define IP_PROTO_TYPE 0x0800
# Define OP_ARP_REQUEST 2
# Define OP_ARP_QUEST 1
# Define DEFAULT_DEVICE "eth0"

Char usage [] =
{"Send_arp: sends out custom ARP packet. ferrysnow@gmail.com usage: send_arp src_ip_addr src_hw_addr targ_ip_addr tar_hw_addr number "};

Struct arp_packet
{
U_char targ_hw_addr [ETH_HW_ADDR_LEN];
U_char src_hw_addr [ETH_HW_ADDR_LEN];
U_short frame_type;
U_short hw_type;
U_short prot_type;
U_char hw_addr_size;
U_char prot_addr_size;
U_short op;
U_char sndr_hw_addr [ETH_HW_ADDR_LEN];
U_char sndr_ip_addr [IP_ADDR_LEN];
U_char rcpt_hw_addr [ETH_HW_ADDR_LEN];
U_char rcpt_ip_addr [IP_ADDR_LEN];
U_char padding [18];
};

Void die (char *);
Void get_ip_addr (struct in_addr *, char *);
Void get_hw_addr (char *, char *);

Int main (int argc, char * argv [])
{
Struct in_addr src_in_addr, targ_in_addr;
Struct arp_packet pkt;
Struct sockaddr sa;
Int sock;
Int j, number;
If (argc! = 6)
{
Die (usage );
}
Sock = socket (AF_INET, SOCK_PACKET, htons (ETH_P_RARP ));
If (sock <0)
{
Perror ("socket ");
Exit (1 );
}
Number = atoi (argv [5]);
Pkt. frame_type = htons (ARP_FRAME_TYPE );
Pkt. hw_type = htons (ETHER_HW_TYPE );
Pkt. prot_type = htons (IP_PROTO_TYPE );
Pkt. hw_addr_size = ETH_HW_ADDR_LEN;
Pkt. prot_addr_size = IP_ADDR_LEN;
Pkt. op = htons (OP_ARP_QUEST );
Get_hw_addr(pkt.tar g_hw_addr, argv [4]);
Get_hw_addr (pkt. rcpt_hw_addr, argv [4]);
Get_hw_addr (pkt. src_hw_addr, argv [2]);
Get_hw_addr (pkt. sndr_hw_addr, argv [2]);
Get_ip_addr (& src_in_addr, argv [1]);
Get_ip_addr (& targ_in_addr, argv [3]);
Memcpy (pkt. sndr_ip_addr, & src_in_addr, IP_ADDR_LEN );
Memcpy (pkt. rcpt_ip_addr, & targ_in_addr, IP_ADDR_LEN );
Bzero (pkt. padding, 18 );
Strcpy (sa. sa_data, DEFAULT_DEVICE );
For (j = 0; j <number; j ++)
{
If (sendto (sock, & pkt, sizeof (pkt), 0, & sa, sizeof (sa) <0)
{
Perror ("sendto ");
Exit (1 );
}
}
Exit (0 );
}

Void die (char * str)
{
Fprintf (stderr, "% s", str );
Exit (1 );
}

Void get_ip_addr (struct in_addr * in_addr, char * str)
{
Struct hostent * hostp;
In_addr-> s_addr = inet_addr (str );
If (in_addr-> s_addr =-1)
{
If (hostp = gethostbyname (str )))
{
Bcopy (hostp-> h_addr, in_addr, hostp-> h_length );
}
Else
{
Fprintf (stderr, "send_arp: unknown host % s", str );
Exit (1 );
}
}
}

Void get_hw_addr (char * buf, char * str)
{
Int I;
Char c, val;
For (I = 0; I <ETH_HW_ADDR_LEN; I ++)
{
If (! (C = tolower (* str ++ )))
{
Die ("Invalid hardware address ");
}
If (isdigit (c ))
{
Val = c-0;
}
Else if (c> = a & c <= f)
{
Val = c-a + 10;
}
Else
{
Die ("Invalid hardware address ");
}
* Buf = val <4;
If (! (C = tolower (* str ++ )))
{
Die ("Invalid hardware address ");
}
If (isdigit (c ))
{
Val = c-0;
}
Else if (c> = a & c <= f)
{
Val = c-a + 10;
}
Else
{
Die ("Invalid hardware address ");
}
* Buf ++ | = val;
If (* str = :)
{
Str ++;
}
}
}