getiflist.cpp

#include <iphlpapi.h>

struct iflist {
	wchar_t name[50];
	struct sockaddr_in sin;
	int ifidx;
};

void getiflist(struct iflist *list, int *listLen)
{
	DWORD dwSize = *listLen;
	DWORD dwRetVal = 0;

	ULONG outBufLen = 15 * 1024; // Allocate a 15 KB buffer to start with.

	PIP_ADAPTER_ADDRESSES pAddresses = nullptr;

	ULONG Iterations = 0;
	do
	{
		if (!(pAddresses = (IP_ADAPTER_ADDRESSES *)HeapAlloc(GetProcessHeap(), 0, outBufLen)))
		{
			printf("Memory allocation failed for IP_ADAPTER_ADDRESSES struct\n");
			return;
		}

		dwRetVal = ::GetAdaptersAddresses(AF_UNSPEC, 0, nullptr, pAddresses, &outBufLen);

		if (dwRetVal == ERROR_BUFFER_OVERFLOW)
		{
			HeapFree(GetProcessHeap(), 0, pAddresses);
			pAddresses = nullptr;
		}
		else
		{
			break;
		}

		Iterations++;

	} while ((dwRetVal == ERROR_BUFFER_OVERFLOW) && (Iterations < 3));

	if (dwRetVal == NO_ERROR)
	{
		PIP_ADAPTER_ADDRESSES pCurrAddresses = nullptr;
		PIP_ADAPTER_UNICAST_ADDRESS pUnicast = nullptr;

		// If successful, output some information from the data we received
		for (*listLen = 0, pCurrAddresses = pAddresses; pCurrAddresses; pCurrAddresses = pCurrAddresses->Next)
		{
			if (pCurrAddresses->IfType == IF_TYPE_TUNNEL
				|| pCurrAddresses->IfType == IF_TYPE_SOFTWARE_LOOPBACK
				|| pCurrAddresses->OperStatus != IfOperStatusUp
				|| pCurrAddresses->Flags & IP_ADAPTER_NO_MULTICAST
				) continue;
			for (pUnicast = pCurrAddresses->FirstUnicastAddress; pUnicast; pUnicast = pUnicast->Next) {
				if (pUnicast->Address.lpSockaddr->sa_family == AF_INET) {
					memset(&list[*listLen], 0, sizeof(struct iflist));
					wcsncpy_s(list[*listLen].name, pCurrAddresses->FriendlyName, sizeof(list[*listLen].name) - 1);
					memcpy(&list[*listLen].sin, pUnicast->Address.lpSockaddr, pUnicast->Address.iSockaddrLength);
					list[*listLen].ifidx = pCurrAddresses->IfIndex;

					(*listLen)++;

					if ((DWORD)*listLen >= dwSize)
						break;
				}
			}
		}
	}
	else
	{
		printf("Call to GetAdaptersAddresses failed with error: %d\n",
			dwRetVal);
		if (dwRetVal == ERROR_NO_DATA)
			printf("\tNo addresses were found for the requested parameters\n");
		else
		{
			LPSTR lpMsgBuf = nullptr;
			if (FormatMessage(FORMAT_MESSAGE_ALLOCATE_BUFFER |
				FORMAT_MESSAGE_FROM_SYSTEM | FORMAT_MESSAGE_IGNORE_INSERTS,
				nullptr, dwRetVal, MAKELANGID(LANG_NEUTRAL, SUBLANG_DEFAULT),
				// Default language
				lpMsgBuf, 0, nullptr))
			{
				printf("\tError: %s", lpMsgBuf);
				LocalFree(lpMsgBuf);
				if (pAddresses) HeapFree(GetProcessHeap(), 0, pAddresses);
				return;
			}
		}
	}

	if (pAddresses) HeapFree(GetProcessHeap(), 0, pAddresses);
}