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Finding out the own IP address

  • Hi there,

    I have, what I think should be, a minor problem. I like to find out the ip address of the machine my application is running. While consulting Qt's documentation I have found QHostInfo, which seemed suitable for my purpose.
    QHostInfo info;
    QString qstr = info.localHostName();
    qDebug() << qstr << endl;
    QHostInfo info2 ( QHostInfo ::fromName ( qstr ) );
    QList <QHostAddress> hostaddr = info2.addresses();
    qDebug () << hostaddr << endl;

    On my machine the code above delivers a list of 6 different ip addresses. Four of them seem to be ipv6 and two ipv4 addresses.
    Four of the addresses (two ipv4 and two ipv6) I could locate. An ipv4 address is the address assigned by the router to my machine. That is actually the address I am looking for. There is also an ipv6 address assigned to the same network adapter. So I can use the ipv6 alternatively, I guess.
    The other pair of ipv4, ipv6 is assigned to my VirtualBox, which is currently not in use. The remaining two ipv6 addresses I do not know where they belong.
    I assume that I can use only 2 of the addresses to communicate with my machine (the ipv4 or the ipv6 address, see above).
    So my basic question is, how do I know which of the addresses is the address I have to use?
    Is the first the choice as suggested "in the example":http://doc.qt.nokia.com/latest/qhostinfo.html#addresses ?

  • If you want to communicate with your local machine, using localhost ( resp. ::1) could be a solution. Most daemons etc. listen on that adress(es) too.

    You could also have a look at the Qt Mobility module (you might need to install it manually). QNetworkSession::interface() seems what you need. I never used it, so this could be complete nonsense - please check first :-)

  • Take care that a machine may have anywhere between 0 to N IP addresses. There is no such thing as the IP address of a machine.

  • Thanks to both of you for your replies.

    @Andre yes, there are certainly several ip addresses available on most machines. Presumably for every hw network adapter installed and possibly a couple of virtual ones.

    @Volker unfortunately, the localhost is no option. I need to know how to communicate from another computer to my machine.
    I followed your suggestion a bit. The good news is, it is not complete nonsense. The bad news is that it did not help yet :-(
    I obtain another QList<QHostAdress> with two more entries (the localhost in ipv4 and ipv6). At least the sequence is different :-) and it is not a step back.
    I think I need to analyse the entries a bit more.

  • at Volker: the interface brought up a solution (see code section below).

    QNetworkConfigurationManager mgr;
    QNetworkConfiguration nconfig = mgr.defaultConfiguration();
    QNetworkSession session ( nconfig );
    QNetworkInterface ninter = session.interface();
    // the next statement gives you a funny name on windows
    qDebug() << ninter.name() << endl;
    // this gives ip addresses in different sequence, but is is a static method anyhow
    // (did not see in first place)
    qDebug() << ninter.allAddresses() << endl;

    // this provides two ip addresses (1 ipv4 and 1 ipv6) at least on my machine
    QList<QNetworkAddressEntry> laddr = ninter.addressEntries();
    for ( QList<QNetworkAddressEntry> ::const_iterator it = laddr.begin(); it != laddr.end(); ++it ) 
        qDebug() << it->ip() << endl;


    If this is really the solution I will find out in the future.

  • I tried the above solution and it failed for the below scenario:
    Connect to internet using PPP adapter through USB and create a wifi adhoc network so that other computers can connect to internet using your internet connection.

    The problem I was facing was that I started a tcpServer on one machine and I wanted to provide the hostIp and port number (Protocol IpV4) to the machines in the local network. So this is what I did:

    @QString getHostIp(){
    QHostInfo hostInfo = QHostInfo::fromName(QHostInfo::localHostName());
    QList<QHostAddress> hostNameLookupAddressList = hostInfo.addresses();
    QList<QHostAddress> interfaceAddressList = QNetworkInterface::allAddresses();
    qDebug()<<FUNCTION<<"hostName lookup addresses:"<<hostNameLookupAddressList;
    qDebug()<<FUNCTION<<"interface addresses:"<<interfaceAddressList;

    QString hostIpStr;
    foreach(QHostAddress addr, hostNameLookupAddressList){
        if(addr.protocol() == QAbstractSocket::IPv4Protocol && interfaceAddressList.contains(addr)){
                qDebug()<<__FUNCTION__<<addr<<" is local ip";
                hostIpStr = addr.toString();
            }else if(isLinkLocalAddress(addr)){
                qDebug()<<__FUNCTION__<<addr<<" is Link Local Address";
                hostIpStr = addr.toString();
    return hostIpStr;


    Link Local address should be in the range to
    Refer :http://en.wikipedia.org/wiki/Private_network
    bool isLinkLocalAddress(QHostAddress addr){
    quint32 hostIpv4Addr = addr.toIPv4Address();
    quint32 rangeMin = QHostAddress("").toIPv4Address();
    quint32 rangeMax = QHostAddress("").toIPv4Address();
    if(hostIpv4Addr >= rangeMin && hostIpv4Addr <= rangeMax){
    return true;
    return false;

    Refer: http://en.wikipedia.org/wiki/Private_network
    Private Ipv4 address ranges:

    1. -
    2. -
    3. -


    bool isLocalIp(QHostAddress addr){
    quint32 hostIpv4Addr = addr.toIPv4Address();
    quint32 range1Min = QHostAddress("").toIPv4Address();
    quint32 range1Max = QHostAddress("").toIPv4Address();

    quint32 range3Min = QHostAddress("").toIPv4Address();
    quint32 range3Max = QHostAddress("").toIPv4Address();
    quint32 range2Min = QHostAddress("").toIPv4Address();
    quint32 range2Max = QHostAddress("").toIPv4Address();
    if((hostIpv4Addr >= range1Min && hostIpv4Addr <= range1Max)
            || (hostIpv4Addr >= range2Min && hostIpv4Addr <= range2Max)
            || (hostIpv4Addr >= range3Min && hostIpv4Addr <= range3Max)){
        return true;
        return false;


  • It's work :)

    foreach (const QHostAddress &address, QNetworkInterface::allAddresses()) {
    if (address.protocol() == QAbstractSocket::IPv4Protocol && address != QHostAddress(QHostAddress::LocalHost)) {
    qDebug() << address.toString();

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