QHostInfo Class

// To find the IP address of qt-project.org
QHostInfo::lookupHost("qt-project.org",
                      this, SLOT(printResults(QHostInfo)));

// To find the host name for 4.2.2.1
QHostInfo::lookupHost("4.2.2.1",
                      this, SLOT(printResults(QHostInfo)));

QHostInfo info = QHostInfo::fromName("qt-project.org");

Member Function Documentation

[since 5.14] QHostInfo::QHostInfo(QHostInfo &&other)

Move-constructs a new QHostInfo from other.

This function was introduced in Qt 5.14.

QHostInfo::QHostInfo(const QHostInfo &other)

Constructs a copy of other.

QHostInfo::QHostInfo(int id = -1)

Constructs an empty host info object with lookup ID id.

See also lookupId().

[since 5.10] QHostInfo &QHostInfo::operator=(QHostInfo &&other)

Move-assigns other to this QHostInfo instance.

This function was introduced in Qt 5.10.

QHostInfo &QHostInfo::operator=(const QHostInfo &other)

Assigns the data of the other object to this host info object, and returns a reference to it.

QHostInfo::~QHostInfo()

Destroys the host info object.

[static] void QHostInfo::abortHostLookup(int id)

Aborts the host lookup with the ID id, as returned by lookupHost().

See also lookupHost() and lookupId().

QList<QHostAddress> QHostInfo::addresses() const

Returns the list of IP addresses associated with hostName(). This list may be empty.

Example:

QHostInfo info;
...
if (!info.addresses().isEmpty()) {
    QHostAddress address = info.addresses().first();
    // use the first IP address
}

See also setAddresses(), hostName(), and error().

QHostInfo::HostInfoError QHostInfo::error() const

Returns the type of error that occurred if the host name lookup failed; otherwise returns NoError.

See also setError() and errorString().

QString QHostInfo::errorString() const

If the lookup failed, this function returns a human readable description of the error; otherwise "Unknown error" is returned.

See also setErrorString() and error().

[static] QHostInfo QHostInfo::fromName(const QString &name)

Looks up the IP address(es) for the given host name. The function blocks during the lookup which means that execution of the program is suspended until the results of the lookup are ready. Returns the result of the lookup in a QHostInfo object.

If you pass a literal IP address to name instead of a host name, QHostInfo will search for the domain name for the IP (i.e., QHostInfo will perform a reverse lookup). On success, the returned QHostInfo will contain both the resolved domain name and IP addresses for the host name.

See also lookupHost().

QString QHostInfo::hostName() const

Returns the name of the host whose IP addresses were looked up.

See also setHostName() and localHostName().

[static] QString QHostInfo::localDomainName()

Returns the DNS domain of this machine.

See also hostName().

[static] QString QHostInfo::localHostName()

Returns this machine's host name, if one is configured. Note that hostnames are not guaranteed to be globally unique, especially if they were configured automatically.

This function does not guarantee the returned host name is a Fully Qualified Domain Name (FQDN). For that, use fromName() to resolve the returned name to an FQDN.

This function returns the same as QSysInfo::machineHostName().

See also hostName() and localDomainName().

[static] int QHostInfo::lookupHost(const QString &name, QObject *receiver, const char *member)

Looks up the IP address(es) associated with host name name, and returns an ID for the lookup. When the result of the lookup is ready, the slot or signal member in receiver is called with a QHostInfo argument. The QHostInfo object can then be inspected to get the results of the lookup.

The lookup is performed by a single function call, for example:

QHostInfo::lookupHost("www.kde.org",
                      this, SLOT(lookedUp(QHostInfo)));

The implementation of the slot prints basic information about the addresses returned by the lookup, or reports an error if it failed:

void MyWidget::lookedUp(const QHostInfo &host)
{
    if (host.error() != QHostInfo::NoError) {
        qDebug() << "Lookup failed:" << host.errorString();
        return;
    }

    const auto addresses = host.addresses();
    for (const QHostAddress &address : addresses)
        qDebug() << "Found address:" << address.toString();
}

If you pass a literal IP address to name instead of a host name, QHostInfo will search for the domain name for the IP (i.e., QHostInfo will perform a reverse lookup). On success, the resulting QHostInfo will contain both the resolved domain name and IP addresses for the host name. Example:

QHostInfo::lookupHost("4.2.2.1",
                      this, SLOT(lookedUp(QHostInfo)));

See also abortHostLookup(), addresses(), error(), and fromName().

[static, since 5.9] template <typename Functor> int QHostInfo::lookupHost(const QString &name, Functor functor)

This is an overloaded function.

Looks up the IP address(es) associated with host name name, and returns an ID for the lookup. When the result of the lookup is ready, the functor is called with a QHostInfo argument. The QHostInfo object can then be inspected to get the results of the lookup.

The functor will be run in the thread that makes the call to lookupHost; that thread must have a running Qt event loop.

This function was introduced in Qt 5.9.

See also abortHostLookup(), addresses(), error(), and fromName().

[static, since 5.9] template <typename Functor> int QHostInfo::lookupHost(const QString &name, const QObject *context, Functor functor)

This is an overloaded function.

Looks up the IP address(es) associated with host name name, and returns an ID for the lookup. When the result of the lookup is ready, the functor is called with a QHostInfo argument. The QHostInfo object can then be inspected to get the results of the lookup.

If context is destroyed before the lookup completes, the functor will not be called. The functor will be run in the thread of context. The context's thread must have a running Qt event loop.

Here is an alternative signature for the function:

lookupHost(const QString &name, const QObject *receiver, PointerToMemberFunction function)

In this case, when the result of the lookup is ready, the slot or signal function in receiver is called with a QHostInfo argument. The QHostInfo object can then be inspected to get the results of the lookup.

This function was introduced in Qt 5.9.

See also abortHostLookup(), addresses(), error(), and fromName().

int QHostInfo::lookupId() const

Returns the ID of this lookup.

See also setLookupId(), abortHostLookup(), and hostName().

void QHostInfo::setAddresses(const QList<QHostAddress> &addresses)

Sets the list of addresses in this QHostInfo to addresses.

See also addresses().

void QHostInfo::setError(QHostInfo::HostInfoError error)

Sets the error type of this QHostInfo to error.

See also error() and errorString().

void QHostInfo::setErrorString(const QString &str)

Sets the human readable description of the error that occurred to str if the lookup failed.

See also errorString() and setError().

void QHostInfo::setHostName(const QString &hostName)

Sets the host name of this QHostInfo to hostName.

See also hostName().

void QHostInfo::setLookupId(int id)

Sets the ID of this lookup to id.

See also lookupId() and lookupHost().

[since 5.10] void QHostInfo::swap(QHostInfo &other)

Swaps host-info other with this host-info. This operation is very fast and never fails.

This function was introduced in Qt 5.10.