Use ioctl() down/change IP/ up interface

I have been trying to create a program in C++ that can take down an interface, change an IP of an interface, or up a downed interface. I have searched around here and found some examples that helped.

However, I am now running into the problem of when I change the IP address of an existing interface lets say eth0, the change occurs correctly, however, I no longer can access the internet until i restart the interface, in which, after the restart, the IP address reverts back to the original IP

#include <sys/ioctl.h>
#include <arpa/inet.h>
#include <net/if.h>
#include <sys/socket.h>
#include <strings.h>
#include <unistd.h>
#include <string.h>
#include <netinet/in.h>
#include <stdio.h>
#include <stdlib.h>
#include <stddef.h>             /* offsetof */
#include <net/if.h>
#include <linux/sockios.h>
#include <netinet/in.h>
#if __GLIBC__ >=2 && __GLIBC_MINOR >= 1
#include <netpacket/packet.h>
#include <net/ethernet.h>
#else
#include <asm/types.h>
#include <linux/if_ether.h>
#endif

#define IFNAME "eth0"
#define HOST "192.168.1.204"
#define ifreq_offsetof(x)  offsetof(struct ifreq, x)

int shared_sock,n, received, receivelen;
struct sockaddr_in receivesocket;
socklen_t len;
char mesg[100];
unsigned char assist_id[] = {0x18, 0xDE, 0x1B};

void test_down(int sockfd){
   //int sockfd;
   struct ifreq ifr;
   //sockfd = socket(AF_INET, SOCK_DGRAM, 0);
   //if (sockfd < 0)
   //    return;
   memset(&ifr, 0, sizeof ifr);
   strncpy(ifr.ifr_name, "eth0", IFNAMSIZ);
   ifr.ifr_flags &= ~IFF_UP;
   ioctl(sockfd, SIOCSIFFLAGS, &ifr);
   //close(sockfd);
}

void test_up(int sockfd){
   //int sockfd;
   struct ifreq ifr;
   //sockfd = socket(AF_INET, SOCK_DGRAM, 0);
  // if (sockfd < 0)
  //     return;
   memset(&ifr, 0, sizeof ifr);
   strncpy(ifr.ifr_name, "eth0", IFNAMSIZ);
   ifr.ifr_flags |= IFF_UP;
   ioctl(sockfd, SIOCSIFFLAGS, &ifr);
   //close(sockfd);
}
void test_function(){
      struct ifreq ifr;
      struct sockaddr_in sai;
      int sockfd;                     /* socket fd we use to manipulate stuff with */
      int selector;
      unsigned char mask;
      char *p;

      /* Create a channel to the NET kernel. */
      sockfd = socket(AF_INET, SOCK_DGRAM, 0);

      /* get interface name */
      strncpy(ifr.ifr_name, IFNAME, IFNAMSIZ);

      memset(&sai, 0, sizeof(struct sockaddr));
      sai.sin_family = AF_INET;
      sai.sin_port = 0;

      sai.sin_addr.s_addr = inet_addr(HOST);

      p = (char *) &sai;
      memcpy( (((char *)&ifr + ifreq_offsetof(ifr_addr) )), p, sizeof(struct sockaddr));

      test_down(sockfd);
      ioctl(sockfd, SIOCSIFADDR, &ifr);
      ioctl(sockfd, SIOCGIFFLAGS, &ifr);

      ifr.ifr_flags |= IFF_UP | IFF_RUNNING;
      // ifr.ifr_flags &= ~selector;  // unset something

      ioctl(sockfd, SIOCSIFFLAGS, &ifr);
      test_up(sockfd);
      close(sockfd);
      return;
}


int main()
{

   shared_sock = socket(PF_INET, SOCK_DGRAM, IPPROTO_UDP);
   /* my address */
   memset(&receivesocket, 0, sizeof(receivesocket));
   receivesocket.sin_family = AF_INET;
   receivesocket.sin_addr.s_addr = htonl(INADDR_ANY);
   receivesocket.sin_port = htons(11000);

   receivelen = sizeof(receivesocket);
   if (bind(shared_sock, (struct sockaddr *) &receivesocket, receivelen) < 0) {
      perror("bind");
      return 1;
   }
   memset(mesg, 0, 100);
   while(true){
      if ((received = recvfrom(shared_sock, mesg, 100, 0, NULL, NULL)) < 0){
         perror("recvfrom");
         return 1;
      }
      printf("Received the following %d:\n", received);
      printf("%s\n",mesg);
      fflush(stdout);
      //test_up();
      test_function();
      //test_up();
   }
   return 0;
}