===== How to add/del route in C =====

<code c>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <unistd.h>

#include <sys/ioctl.h>
#include <linux/route.h>

#define ROUTE_ADD SIOCADDRT
#define ROUTE_DEL SIOCDELRT

int route_edit(int action, struct sockaddr_in destination, struct sockaddr_in gateway);

int
main (int argc, char *argv[])
{
  struct sockaddr_in dest, gw;

  /* Fill structures with 0 */
  memset (&dest, 0, sizeof(dest));
  memset (&gw, 0, sizeof(gw));

  dest.sin_family = AF_INET;
  dest.sin_addr.s_addr = inet_addr("1.2.3.4");
  gw.sin_family = AF_INET;
  gw.sin_addr.s_addr = inet_addr("127.0.0.1");

  printf("-> %d\n", route_edit(ROUTE_ADD, dest, gw));
  printf("-> %d\n", route_edit(ROUTE_DEL, dest, gw));
  exit (0);
}

/* Add or delete a route  */
int
route_edit(int action, struct sockaddr_in destination, struct sockaddr_in gateway)
{
  struct rtentry new_route;
  int skt;
  /* Fill structure */
  memset(&new_route, 0, sizeof(struct rtentry));

  /* Copy sockadd_in structure to new_route */
  memcpy((char *) &new_route.rt_dst, (char *) &destination, (sizeof destination));
  memcpy((char *) &new_route.rt_gateway, (char *) &gateway, (sizeof gateway));

  /* Open socket */
  if ((skt = socket(AF_INET, SOCK_DGRAM, 0)) < 0)
    return -1;

  /* Proceed */
  {
    int ret;
    ret = ioctl(skt, action, &new_route);
    /* Close socket */
    close (skt);
    return ret;
  }
}

</code>

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