Obtain and modify the netmask subnet mask in Linux.

// Obtain the subnet mask FunctionQstring getlocalnetmask () <br/>{< br/> int sock_netmask; <br/> char netmask_addr [50]; </P> <p> struct ifreq ifr_mask; <br/> struct sockaddr_in * net_mask; </P> <p> sock_netmask = socket (af_inet, sock_stream, 0); <br/> If (sock_netmask =-1) <br/>{< br/> perror ("create socket failture... getlocalnetmask/N "); <br/> return" "; <br/>}</P> <p> memset (& ifr_mask, 0, sizeof (ifr_mask )); <br/> strncpy (signature, ifname, sizeof (ifr_mask.ifr_name)-1); </P> <p> If (IOCTL (sock_netmask, siocgifnetmask, & ifr_mask )) <0) <br/>{< br/> printf ("Mac IOCTL error/N"); <br/> return ""; <br/>}</P> <p> net_mask = (struct sockaddr_in *) & (ifr_mask.ifr_netmask); <br/> strcpy (netmask_addr, inet_ntoa (net_mask-> sin_addr); </P> <p> printf ("Local netmask: % s/n", netmask_addr ); </P> <p> close (sock_netmask); <br/> return qstring (netmask_addr); <br/>}

// Modify the subnetmask Function

Qstring setlocalnetmask (const char * sznetmask) <br/>{< br/> int sock_netmask; <br/> char netmask_addr [32]; </P> <p> struct ifreq ifr_mask; <br/> struct sockaddr_in * sin_net_mask; </P> <p> sock_netmask = socket (af_inet, sock_stream, 0 ); <br/> If (sock_netmask =-1) <br/> {<br/> perror ("not create network socket connect/N "); <br/> return ""; <br/>}</P> <p> memset (& ifr_mask, 0, sizeof (ifr_mask )); <br/> strncpy (ifr_mask.ifr_name, "eth0", sizeof (ifr_mask.ifr_name)-1); <br/> sin_net_mask = (struct sockaddr_in *) & signature; <br/> sin_net_mask-> sin_family = af_inet; <br/> inet_pton (af_inet, sznetmask, & sin_net_mask-> sin_addr ); </P> <p> If (IOCTL (sock_netmask, siocsifnetmask, & ifr_mask) <0) <br/>{< br/> printf ("sock_netmask IOCTL error/N"); <br/> return "; <br/>}< br/>}