Releasing DHCP oriented IP address

Sample code

The following sample code shows how to use IpReleaseAddress(). The following sample releases the IP address assigned to all the network interfaces. The following sample works like the command "ipconfig /release".

List of network interfaces can be obtained using GetInterfaceInfo(). IpReleaseAddress() uses the network adapter structure which can be obtained by GetInterfaceInfo().

#include <stdio.h>

#include <winsock2.h>
#include <iphlpapi.h>

int
main()
{
 int i;
 PIP_INTERFACE_INFO pInfo = NULL;
 ULONG ulOutBufLen = 0;
 DWORD dwRetVal = 0;

 /* Get ulOutBufLen size */
 if (GetInterfaceInfo(NULL, &ulOutBufLen)
       == ERROR_INSUFFICIENT_BUFFER) {
   pInfo = (IP_INTERFACE_INFO *) malloc (ulOutBufLen);
 }

 /* Get the actual data. */
 dwRetVal = GetInterfaceInfo(pInfo, &ulOutBufLen);

 if (dwRetVal == NO_ERROR ) {
   printf("Number of Adapters: %ld\n\n", pInfo->NumAdapters);

   for (i=0; i<pInfo->NumAdapters; i++) {
     printf("Adapter Name: %ws\n", pInfo->Adapter[i].Name);
     printf("Adapter Index: %ld\n", pInfo->Adapter[i].Index);

     if (IpReleaseAddress(&pInfo->Adapter[i]) == NO_ERROR) {
      printf("released\n");
     } else {
      printf("release failed\n");
     }

     printf("\n");
   }
 } else {
   printf("GetInterfaceInfo failed.\n");
   LPVOID lpMsgBuf;
		
   if (FormatMessage(
           FORMAT_MESSAGE_ALLOCATE_BUFFER | 
           FORMAT_MESSAGE_FROM_SYSTEM | 
           FORMAT_MESSAGE_IGNORE_INSERTS,
           NULL,
           dwRetVal,
           MAKELANGID(LANG_NEUTRAL,
                      SUBLANG_DEFAULT), /* Default language */
           (LPTSTR) &lpMsgBuf,
           0,
           NULL ))  {
     printf("Error: %s", lpMsgBuf);
   }

   LocalFree( lpMsgBuf );
 }

 return 0;
}

Sample code output

The sample will output an message like the following.

C:> a.exe
Number of Adapters: 2

Adapter Name: \DEVICE\TCPIP_{22EXXC3D-F01D-4231-AE59-C23EXXXX6C66}
Adapter Index: 2
released

Adapter Name: \DEVICE\TCPIP_{4E7XX61B-836C-49AB-8B02-775BXXXX7352}
Adapter Index: 3
released