C Replace String Example

#include
#include

char *replace(char *st, char *orig, char *repl) {
static char buffer[4096];
char *ch;
if (!(ch = strstr(st, orig)))
return st;
strncpy(buffer, st, ch-st);
buffer[ch-st] = 0;
sprintf(buffer+(ch-st), "%s%s", repl, ch+strlen(orig));
return buffer;
}
void main() {
puts(replace("Hello world!", "world", "India"));
}

Detecting MAC Address using C application

#include 
#include 
#include 
#include 
#include 

#ifdef Linux
#include 
#include 
#include 
#include 
#include 
#endif

#ifdef HPUX
#include 
#endif

#ifdef AIX
#include 
#include 
#endif

long mac_addr_sys ( u_char *addr)
{
/* implementation for Linux */
#ifdef Linux
   struct ifreq ifr;
   struct ifreq *IFR;
   struct ifconf ifc;
   char buf[1024];
   int s, i;
   int ok = 0;

   s = socket(AF_INET, SOCK_DGRAM, 0);
   if (s==-1) {
       return -1;
   }

   ifc.ifc_len = sizeof(buf);
   ifc.ifc_buf = buf;
   ioctl(s, SIOCGIFCONF, &ifc);

   IFR = ifc.ifc_req;
   for (i = ifc.ifc_len / sizeof(struct ifreq); --i >= 0; IFR++) {

       strcpy(ifr.ifr_name, IFR->ifr_name);
       if (ioctl(s, SIOCGIFFLAGS, &ifr) == 0) {
           if (! (ifr.ifr_flags & IFF_LOOPBACK)) {
               if (ioctl(s, SIOCGIFHWADDR, &ifr) == 0) {
                   ok = 1;
                   break;
               }
           }
       }
   }

   close(s);
   if (ok) {
       bcopy( ifr.ifr_hwaddr.sa_data, addr, 6);
   }
   else {
       return -1;
   }
   return 0;
#endif

/* implementation for HP-UX */
#ifdef HPUX

#define LAN_DEV0 "/dev/lan0"

   intfd;
   struct fisiocnt_block;
   inti;
   charnet_buf[sizeof(LAN_DEV0)+1];
   char*p;

   (void)sprintf(net_buf, "%s", LAN_DEV0);
   p = net_buf + strlen(net_buf) - 1;

   /*
    * Get 802.3 address from card by opening the driver and interrogating it.
    */
   for (i = 0; i < 10; i++, (*p)++) {
       if ((fd = open (net_buf, O_RDONLY)) != -1) {
iocnt_block.reqtype = LOCAL_ADDRESS;
ioctl (fd, NETSTAT, &iocnt_block);
close (fd);

           if (iocnt_block.vtype == 6)
               break;
       }
   }

   if (fd == -1 || iocnt_block.vtype != 6) {
       return -1;
   }

bcopy( &iocnt_block.value.s[0], addr, 6);
return 0;

#endif /* HPUX */

/* implementation for AIX */
#ifdef AIX

   int size;
   struct kinfo_ndd *nddp;

   size = getkerninfo(KINFO_NDD, 0, 0, 0);
   if (size <= 0) {
       return -1;
   }
   nddp = (struct kinfo_ndd *)malloc(size);

   if (!nddp) {
       return -1;
   }
   if (getkerninfo(KINFO_NDD, nddp, &size, 0) < 0) {
       free(nddp);
       return -1;
   }
   bcopy(nddp->ndd_addr, addr, 6);
   free(nddp);
   return 0;
#endif

/* Not implemented platforms */
return -1;
}

/***********************************************************************/
/*
* Main (only for testing)
*/
#ifdef MAIN
int main( int argc, char **argv)
{
   long stat;
   int i;
   u_char addr[6];

   stat = mac_addr_sys( addr);
   if (0 == stat) {
       printf( "MAC address = ");
       for (i=0; i<6; ++i) {
           printf("%2.2x", addr[i]);
       }
       printf( "\n");
   }
   else {
       fprintf( stderr, "can't get MAC address\n");
       exit( 1);
   }
   return 0;
}
#endif

E.g you want to use on Linux, save it as file.c simply compile like this:

   gcc -O2 -DMAIN -DLinux file.c -o file

And run it

./file
MAC address = 0008c7e9e386

Compare with /sbin/ifconfig result:

/sbin/ifconfig eth0
eth0      Link encap:Ethernet  HWaddr 00:08:C7:E9:E3:86
         inet addr:***.***.***.***  Bcast:***.***.***.***  Mask:255.255.255.0
         inet6 addr: ********************* Scope:Link
         UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
         RX packets:265555947 errors:0 dropped:0 overruns:0 frame:0
         TX packets:50507373 errors:0 dropped:0 overruns:0 carrier:0
         collisions:0 txqueuelen:1000
         RX bytes:4090310752 (3.8 GiB)  TX bytes:1085018636 (1.0 GiB)

It’s the same