NotifyAddrChange function (iphlpapi.h)

Article
10/13/2021

The NotifyAddrChange function causes a notification to be sent to the caller whenever a change occurs in the table that maps IPv4 addresses to interfaces.

Syntax

IPHLPAPI_DLL_LINKAGE DWORD NotifyAddrChange(
  [out] PHANDLE      Handle,
  [in]  LPOVERLAPPED overlapped
);

Parameters

[out] Handle

A pointer to a HANDLE variable that receives a file handle for use in a subsequent call to the GetOverlappedResult function.

Warning Do not close this handle, and do not associate it with a completion port.

[in] overlapped

A pointer to an OVERLAPPED structure that notifies the caller of any changes in the table that maps IP addresses to interfaces.

Return value

If the function succeeds, the return value is NO_ERROR if the caller specifies NULL for the Handle and overlapped parameters. If the caller specifies non-NULL parameters, the return value for success is ERROR_IO_PENDING.

If the function fails, use FormatMessage to obtain the message string for the returned error.

Return code	Description
ERROR_CANCELLED	The context is being deregistered, so the call was canceled immediately.
ERROR_INVALID_PARAMETER	An invalid parameter was passed. This error is returned if the both the Handle and overlapped parameters are not NULL, but the memory specified by the input parameters cannot be written by the calling process. This error is also returned if the client already has made a change notification request, so this duplicate request will fail.
ERROR_NOT_ENOUGH_MEMORY	There was insufficient memory available to complete the operation.
ERROR_NOT_SUPPORTED	This error is returned on versions of Windows where this function is not supported such as Windows 98/95 and Windows NT 4.0.

Remarks

The
NotifyAddrChange function may be called in two ways:

Synchronous method
Asynchronous method

If the caller specifies NULL for the Handle and overlapped parameters, the call to NotifyAddrChange is synchronous and will block until an IP address change occurs. In this case if a change occurs, the NotifyAddrChange function completes to indicate that a change has occurred.

If the NotifyAddrChange function is called synchronously, a notification will be sent on the next IPv4 address change until the application terminates.

If the caller specifies a handle variable and an OVERLAPPED structure, then the NotifyAddrChange function call is asynchronous and the caller can use the returned handle with the OVERLAPPED structure to receive asynchronous notification of IPv4 address changes using the GetOverlappedResult function. See the following topics for information about using the handle and OVERLAPPED structure to receive notifications:

The CancelIPChangeNotify function cancels notification of IPv4 address and route changes previously requested with successful calls to the NotifyAddrChange or NotifyRouteChange functions.

Once an application has been notified of a change, the application can then call the GetIpAddrTable or GetAdaptersAddresses function to retrieve the table of IPv4 addresses to determine what has changed. If the application is notified and requires notification for the next change, then the NotifyAddrChange function must be called again.

If the NotifyAddrChange function is called asynchronously, a notification will be sent on the next IPv4 address change until either the application cancels the notification by calling the CancelIPChangeNotify function or the application terminates. If the application terminates, the system will automatically cancel the registration for the notification. It is still recommended that an application explicitly cancel any notification before it terminates.

Any registration for a notification does not persist across a system shut down or reboot.

On Windows Vista and later, the NotifyIpInterfaceChange function can be used to register to be notified for changes to IPv4 and IPv6 interfaces on the local computer.

Examples

The following example waits for a change to occur in the table that maps IP addresses to interfaces.

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

#pragma comment(lib, "iphlpapi.lib")
#pragma comment(lib, "ws2_32.lib")

void main()
{
  OVERLAPPED overlap;
  DWORD ret;
    
  HANDLE hand = NULL;
  overlap.hEvent = WSACreateEvent();

  ret = NotifyAddrChange(&hand, &overlap);

  if (ret != NO_ERROR)
  {
    if (WSAGetLastError() != WSA_IO_PENDING)
    {
      printf("NotifyAddrChange error...%d\n", WSAGetLastError());            
      return;
    }
  }

  if ( WaitForSingleObject(overlap.hEvent, INFINITE) == WAIT_OBJECT_0 )
    printf("IP Address table changed..\n");
}

Requirements

Requirement	Value
Minimum supported client	Windows 2000 Professional [desktop apps only]
Minimum supported server	Windows 2000 Server [desktop apps only]
Target Platform	Windows
Header	iphlpapi.h
Library	Iphlpapi.lib
DLL	Iphlpapi.dll

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