Linux system obtains network IP addresses, mask, gateway, and DNS information applets

Net_util.c

# Define wired_dev "eth0"
# Define wireless_dev "ra0"
# Define pppoe_dev "ppp0"

# Define debug_prt (FMT, Arg...) printf (FMT, # Arg)

/**
* Get IP address.
* @ Param net_dev net device.
* @ Param ipaddr a pointer to save IP address.
* @ Return 0 success, or fail.
*/
Int get_ipaddr (const char * net_dev, char * ipaddr)
{
Struct ifreq IFR;
Int FD = 0;
Struct sockaddr_in * paddr;

If (null = net_dev) | (null = ipaddr ))
{
Debug_prt ("illegal call function setgeneralip! \ N ");
Return-1;
}

If (FD = socket (af_inet, sock_dgram, 0) <0)
{
Debug_prt ("Open socket failed \ n ");
Return-1;
}

Memset (& IFR, 0, sizeof (IFR ));
Strcpy (IFR. ifr_name, net_dev );

If (IOCTL (FD, siocgifaddr, & IFR) <0)
{
Debug_prt ("siocgifaddr socket failed \ n ");
Close (FD );
Return-1;
}

Paddr = (struct sockaddr_in *) & (IFR. ifr_addr );

Strcpy (ipaddr, inet_ntoa (paddr-> sin_addr ));

Close (FD );

Return 0;
}

/**
* Get gateway.
* @ Param gateway a pointer to save geteway.
* @ Return none.
*/
Void get_gateway (iti_char * gateway)
{
Char Buf [1024] = {0 };
Char * P = NULL;
Char * q = NULL;
Int COUNT = 0;
If (null = gateway)
{
Debug_prt ("Gateway is null \ n ");
Return;
}
Performance_run ("route | grep default", Buf, 1024 );
If (0 = strlen (BUF ))
{
Debug_prt ("Get Gateway error \ n ");
Return;
}

P = strstr2 (BUF, "default ");
Q = P;
While (* q = '')
{
Q ++;
}

P = Q;
While (* P! = '')
{
P ++;
Count ++;
}
If (null! = Q)
{
Memcpy (gateway, Q, count );
}
Gateway [count] = '\ 0 ';
}

/**
* Get mask.
* @ Param net_dev net device.
* @ Param mask a pointer to save mask.
* @ Return none.
*/
Void get_mask (const char * net_dev, iti_char * mask)
{
Char Buf [1024] = {0 };
Char * P = NULL;
If (null = mask)
{
Debug_prt ("Mask is null \ n ");
Return;
}
If (0 = (memcmp (wired_dev, net_dev, sizeof (wired_dev ))))
{
Performance_run ("ifconfig eth0 | grep mask", Buf, 1024 );
}
Else if (0 = (memcmp (wireless_dev, net_dev, sizeof (wireless_dev ))))
{
Performance_run ("ifconfig ra0 | grep mask", Buf, 1024 );
}
Else if (0 = (memcmp (pppoe_dev, net_dev, sizeof (pppoe_dev ))))
{
Performance_run ("ifconfig ppp0 | grep mask", Buf, 1024 );
}
Else
{
Debug_prt ("net device not support \ n ");
Return;
}

If (0 = strlen (BUF ))
{
Debug_prt ("Get mask error \ n ");
Return;
}
P = strstr2 (BUF, "Mask :");
If (null = P)
{
Debug_prt ("Get mask error \ n ");
Return;
}
Strcpy (mask, P );
}

/**
* Get DNS.
* @ Param dns1 a pointer to save first DNS.
* @ Param dns2 a pointer to save second DNS.
* @ Return 0 success, or fail.
*/
Int get_dns (char * dns1, char * dns2)
{
Int FD =-1;
Int size = 0;
Char strbuf [100];
Char tmpbuf [100];
Int buf_size = sizeof (strbuf );
Char * P = NULL;
Char * q = NULL;
Int I = 0;
Int J = 0;
Int COUNT = 0;

FD = open ("/etc/resolv. conf", o_rdonly );
If (-1 = FD)
{
Debug_prt ("% s open error \ n", _ FUNC __);
Return-1;
}
Size = read (FD, strbuf, buf_size );
If (size <0)
{
Debug_prt ("% s Read File Len error \ n", _ FUNC __);
Close (FD );
Return-1;
}
Strbuf [buf_size] = '\ 0 ';
Close (FD );

While (I <buf_size)
{
If (P = strstr2 (& strbuf [I], "nameserver "))! = NULL)
{
J ++;
P + = 1;
Count = 0;

Memset (tmpbuf, 0xff, 100 );
Memcpy (tmpbuf, P, 100 );
Tmpbuf [sizeof (tmpbuf)-1] = '\ 0 ';

Q = P;
While (* Q! = '\ N ')
{
Q ++;
Count ++;
}
I + = (sizeof ("nameserver") + count );

If (1 = J)
{
Memcpy (dns1, P, count );
Dns1 [count] = '\ 0 ';
}
Else if (2 = J)
{
Memcpy (dns2, P, count );
Dns2 [count] = '\ 0 ';
}
}
Else
{
I ++;
}
}

Return 0;
}

Main. c

Void main (void)

{

# Define wired_dev "eth0"
# Define wireless_dev "ra0"
# Define pppoe_dev "ppp0"

Char Buf [1024] = {'\ 0 '};

Extern int get_ipaddr (const char * net_dev, char * ipaddr );
Get_ipaddr (wired_dev, Buf );
Printf ("get_ipaddr: % s \ n", Buf );
Memset (BUF, '\ 0', sizeof (BUF ));

Extern void get_mask (const char * net_dev, iti_char * mask );
Get_mask (wired_dev, Buf );
Printf ("get_mask: % s \ n", Buf );
Memset (BUF, '\ 0', sizeof (BUF ));

Extern void get_gateway (iti_char * gateway );
Get_gateway (BUF );
Printf ("get_gateway: % s \ n", Buf );
Memset (BUF, '\ 0', sizeof (BUF ));

Extern int get_dns (char * dns1, char * dns2 );
Get_dns (BUF, & Buf [1, 100]);
Printf ("get_dns: % S % s \ n", Buf, & Buf [100]);
Memset (BUF, '\ 0', sizeof (BUF ));

}

Makefile:

GCC main. c net_util.c-O get_net_info

./Get_net_info

Running result:

Get_ipaddr: 192.168.9.142
Get_mask: 255.255.255.0
Get_gateway: 192.168.9.254
Get_dns: 192.168.9.11 192.168.9.10

To improve execution efficiency, update the program for obtaining the gateway and subnet mask:

Static void get_gateway (const char * net_dev, char * gateway)
{
File * FP;
Char Buf [1024];
Char iface [16];
Unsigned char TMP [100] = {'\ 0 '};
Unsigned int dest_addr = 0, gate_addr = 0;
If (null = gateway)
{
Debug_prt ("Gateway is null \ n ");
Return;
}
Fp = fopen ("/proc/NET/route", "R ");
If (FP = NULL ){
Debug_prt ("fopen error \ n ");
Return;
}

Fgets (BUF, sizeof (BUF), FP );
While (fgets (BUF, sizeof (BUF), FP ))
{
If (sscanf (BUF, "% s \ t % x", iface, & dest_addr, & gate_addr) = 3)
& (Memcmp (net_dev, iface, strlen (net_dev) = 0)
& Gate_addr! = 0)
{
Memcpy (TMP, (unsigned char *) & gate_addr, 4 );
Sprintf (gateway, "% d. % d. % d. % d ", (unsigned char) * TMP, (unsigned char) * (TMP + 1), (unsigned char) * (TMP + 2), (unsigned char) * (TMP + 3 ));
Break;
}
}

Fclose (FP );
}

Static void get_mask (const char * net_dev, iti_char * mask)
{
Struct sockaddr_in * paddr;
Struct ifreq IFR;
Int sockfd;

Sockfd = socket (af_inet, sock_dgram, 0 );
Memset (& IFR, 0, sizeof (IFR ));
Strcpy (IFR. ifr_name, net_dev );

If (IOCTL (sockfd, siocgifnetmask, & IFR) <0 ){
Debug_prt ("siocgifaddr socket failed \ n ");
Close (sockfd );
Return;
}

Paddr = (struct sockaddr_in *) & (IFR. ifr_addr );
Strcpy (mask, (char *) (inet_ntoa (paddr-> sin_addr )));

Close (sockfd );
}