This example shows how to get the computer's network interface list, along with associated information like the broadcast addresses, the netmasks, and some of the interface's capabilities. This program is actually a semi-useful tool, sort of like an output-only version of the Unix ifconfig program. However, its output is significantly more readable.

This program requires Winsock 2. It definitely works under Windows NT 4.0 if you have at least Service Pack 3 installed and perhaps also under Windows 98. This sample reportedly does not work on Windows 95.

getifaces.cpp

// Borland C++ 5.0: bcc32.cpp getifaces.cpp ws2_32.lib
// Visual C++ 5.0: cl getifaces.cpp ws2_32.lib 

#include <iostream.h>
#include <winsock2.h>
#include <ws2tcpip.h>

int doit()
{
    SOCKET sd = WSASocket(AF_INET, SOCK_DGRAM, 0, 0, 0, 0);
    if (sd == SOCKET_ERROR) {
        cerr << "Failed to get a socket. Error " << WSAGetLastError() <<
            endl; return 1;
    }

    INTERFACE_INFO InterfaceList[20];
    unsigned long nBytesReturned;
    if (WSAIoctl(sd, SIO_GET_INTERFACE_LIST, 0, 0, &InterfaceList,
			sizeof(InterfaceList), &nBytesReturned, 0, 0) == SOCKET_ERROR) {
        cerr << "Failed calling WSAIoctl: error " << WSAGetLastError() <<
				endl;
		return 1;
    }

    int nNumInterfaces = nBytesReturned / sizeof(INTERFACE_INFO);
    cout << "There are " << nNumInterfaces << " interfaces:" << endl;
    for (int i = 0; i < nNumInterfaces; ++i) {
        cout << endl;

        sockaddr_in *pAddress;
        pAddress = (sockaddr_in *) & (InterfaceList[i].iiAddress);
        cout << " " << inet_ntoa(pAddress->sin_addr);

        pAddress = (sockaddr_in *) & (InterfaceList[i].iiBroadcastAddress);
        cout << " has bcast " << inet_ntoa(pAddress->sin_addr);

        pAddress = (sockaddr_in *) & (InterfaceList[i].iiNetmask);
        cout << " and netmask " << inet_ntoa(pAddress->sin_addr) << endl;

        cout << " Iface is ";
        u_long nFlags = InterfaceList[i].iiFlags;
        if (nFlags & IFF_UP) cout << "up";
        else                 cout << "down";
        if (nFlags & IFF_POINTTOPOINT) cout << ", is point-to-point";
        if (nFlags & IFF_LOOPBACK)     cout << ", is a loopback iface";
        cout << ", and can do: ";
        if (nFlags & IFF_BROADCAST) cout << "bcast ";
        if (nFlags & IFF_MULTICAST) cout << "multicast ";
        cout << endl;
    }

    return 0;
}

int main()
{
    WSADATA WinsockData;
    if (WSAStartup(MAKEWORD(2, 2), &WinsockData) != 0) {
        cerr << "Failed to find Winsock 2.2!" << endl;
        return 2;
    }

    int nRetVal = doit();

    WSACleanup();

    return nRetVal;
}