The QHostInfo class provides static functions for host name lookups. More...

#include <qhostinfo.h>

Collaboration diagram for QHostInfo:

Public Types
enum	HostInfoError { NoError , HostNotFound , UnknownError }
	This enum describes the various errors that can occur when trying to resolve a host name. More...

Public Member Functions
	QHostInfo (int lookupId=-1)
	Constructs an empty host info object with lookup ID id.

	QHostInfo (const QHostInfo &d)
	Constructs a copy of other.

	QHostInfo (QHostInfo &&other) noexcept
	Move-constructs a new QHostInfo from other.

QHostInfo &	operator= (const QHostInfo &d)
	Assigns the data of the other object to this host info object, and returns a reference to it.

QHostInfo &	operator= (QHostInfo &&other) noexcept
	Move-assigns other to this QHostInfo instance.

	~QHostInfo ()
	Destroys the host info object.

void	swap (QHostInfo &other) noexcept
	\memberswap{host-info}

QString	hostName () const
	Returns the name of the host whose IP addresses were looked up.

void	setHostName (const QString &name)
	Sets the host name of this QHostInfo to hostName.

QList< QHostAddress >	addresses () const
	Returns the list of IP addresses associated with hostName().

void	setAddresses (const QList< QHostAddress > &addresses)
	Sets the list of addresses in this QHostInfo to addresses.

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

void	setError (HostInfoError error)
	Sets the error type of this QHostInfo to error.

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

void	setErrorString (const QString &errorString)
	Sets the human readable description of the error that occurred to str if the lookup failed.

void	setLookupId (int id)
	Sets the ID of this lookup to id.

int	lookupId () const
	Returns the ID of this lookup.

Static Public Member Functions
static int	lookupHost (const QString &name, const QObject receiver, const char member)
	Looks up the IP address(es) associated with host name name, and returns an ID for the lookup.

static void	abortHostLookup (int lookupId)
	Aborts the host lookup with the ID id, as returned by lookupHost().

static QHostInfo	fromName (const QString &name)
	Looks up the IP address(es) for the given host name.

static QString	localHostName ()
	Returns this machine's host name, if one is configured.

static QString	localDomainName ()
	Returns the DNS domain of this machine.

template<typename Functor >
static int	lookupHost (const QString &name, const typename QtPrivate::ContextTypeForFunctor< Functor >::ContextType *receiver, Functor &&func)

template<typename Functor >
static int	lookupHost (const QString &name, Functor &&slot)

Friends
QHostInfo Q_NETWORK_EXPORT	qt_qhostinfo_lookup (const QString &name, QObject receiver, const char member, bool valid, int id)

Detailed Description

The QHostInfo class provides static functions for host name lookups.

\reentrant \inmodule QtNetwork

QHostInfo finds the IP address(es) associated with a host name, or the host name associated with an IP address. The class provides two static convenience functions: one that works asynchronously and emits a signal once the host is found, and one that blocks and returns a QHostInfo object.

To look up a host's IP addresses asynchronously, call lookupHost(), which takes the host name or IP address, a receiver object, and a slot signature as arguments and returns an ID. You can abort the lookup by calling abortHostLookup() with the lookup ID.

Example:

// To find the IP address of qt-project.org
QHostInfo::lookupHost("qt-project.org", this, &MyWidget::printResults);
 
// To find the host name for 4.2.2.1
QHostInfo::lookupHost("4.2.2.1", this, &MyWidget::printResults);

The slot is invoked when the results are ready. The results are stored in a QHostInfo object. Call addresses() to get the list of IP addresses for the host, and hostName() to get the host name that was looked up.

If the lookup failed, error() returns the type of error that occurred. errorString() gives a human-readable description of the lookup error.

If you want a blocking lookup, use the QHostInfo::fromName() function:

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

QHostInfo supports Internationalized Domain Names (IDNs) through the IDNA and Punycode standards.

To retrieve the name of the local host, use the static QHostInfo::localHostName() function.

QHostInfo uses the mechanisms provided by the operating system to perform the lookup. As per \l {RFC 6724} there is no guarantee that all IP addresses registered for a domain or host will be returned.

Note: Since Qt 4.6.1 QHostInfo is using multiple threads for DNS lookup instead of one dedicated DNS thread. This improves performance, but also changes the order of signal emissions when using lookupHost() compared to previous versions of Qt.; Since Qt 4.6.3 QHostInfo is using a small internal 60 second DNS cache for performance improvements.

See also: QAbstractSocket, {RFC 3492}, {RFC 6724}

Definition at line 18 of file qhostinfo.h.

Member Enumeration Documentation

◆ HostInfoError

enum QHostInfo::HostInfoError

This enum describes the various errors that can occur when trying to resolve a host name.

\value NoError The lookup was successful. \value HostNotFound No IP addresses were found for the host. \value UnknownError An unknown error occurred.

See also: error(), setError()

Enumerator
NoError
HostNotFound
UnknownError

Definition at line 22 of file qhostinfo.h.

Constructor & Destructor Documentation

◆ QHostInfo() [1/3]

QHostInfo::QHostInfo ( int id = -1 )

explicit

Constructs an empty host info object with lookup ID id.

See also: lookupId()

Definition at line 527 of file qhostinfo.cpp.

◆ QHostInfo() [2/3]

QHostInfo::QHostInfo ( const QHostInfo & d )

Constructs a copy of other.

Definition at line 537 of file qhostinfo.cpp.

◆ QHostInfo() [3/3]

QHostInfo::QHostInfo ( QHostInfo && other )

inlinenoexcept

Move-constructs a new QHostInfo from other.

Note: The moved-from object other is placed in a partially-formed state, in which the only valid operations are destruction and assignment of a new value.

Since: 5.14

Definition at line 30 of file qhostinfo.h.

◆ ~QHostInfo()

QHostInfo::~QHostInfo ( )

Destroys the host info object.

Definition at line 571 of file qhostinfo.cpp.

Member Function Documentation

◆ abortHostLookup()

void QHostInfo::abortHostLookup ( int id )

static

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

See also: lookupHost(), lookupId()

Definition at line 317 of file qhostinfo.cpp.

◆ addresses()

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: hostName(), error()

Definition at line 586 of file qhostinfo.cpp.

◆ 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(), errorString()

Definition at line 631 of file qhostinfo.cpp.

◆ 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(), error()

Definition at line 676 of file qhostinfo.cpp.

◆ fromName()

QHostInfo QHostInfo::fromName ( const QString & name )

static

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()

Definition at line 335 of file qhostinfo.cpp.

◆ hostName()

QString QHostInfo::hostName ( ) const

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

See also: localHostName()

Definition at line 608 of file qhostinfo.cpp.

◆ localDomainName()

QString QHostInfo::localDomainName ( )

static

Returns the DNS domain of this machine.

Note: DNS domains are not related to domain names found in Windows networks.

See also: hostName()

Definition at line 96 of file qhostinfo_unix.cpp.

◆ localHostName()

QString QHostInfo::localHostName ( )

static

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(), localDomainName()

Definition at line 709 of file qhostinfo.cpp.

◆ lookupHost() [1/3]

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

static

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, &MyWidget::lookedUp);

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, &MyWidget::lookedUp);

Note: There is no guarantee on the order the signals will be emitted if you start multiple requests with lookupHost().; In Qt versions prior to 6.7, this function took receiver as (non-const) {QObject*}.

See also: abortHostLookup(), addresses(), error(), fromName()

Definition at line 229 of file qhostinfo.cpp.

◆ lookupHost() [2/3]

template<typename Functor >

static int QHostInfo::lookupHost	(	const QString &	name,
		const typename QtPrivate::ContextTypeForFunctor< Functor >::ContextType *	receiver,
		Functor &&	func )

inlinestatic

Definition at line 68 of file qhostinfo.h.

◆ lookupHost() [3/3]

template<typename Functor >

static int QHostInfo::lookupHost	(	const QString &	name,
		Functor &&	functor )

inlinestatic

Since: 5.9

This is an overloaded member function, provided for convenience. It differs from the above function only in what argument(s) it accepts.

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.

Note: There is no guarantee on the order the signals will be emitted if you start multiple requests with lookupHost().

See also: abortHostLookup(), addresses(), error(), fromName()

Definition at line 83 of file qhostinfo.h.

◆ lookupId()

int QHostInfo::lookupId ( ) const

Returns the ID of this lookup.

See also: setLookupId(), abortHostLookup(), hostName()

Definition at line 653 of file qhostinfo.cpp.

◆ operator=() [1/2]

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

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

Definition at line 558 of file qhostinfo.cpp.

◆ operator=() [2/2]

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

inlinenoexcept

Move-assigns other to this QHostInfo instance.

Note: The moved-from object other is placed in a partially-formed state, in which the only valid operations are destruction and assignment of a new value.

Since: 5.10

Definition at line 32 of file qhostinfo.h.

◆ setAddresses()

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

Sets the list of addresses in this QHostInfo to addresses.

See also: addresses()

Definition at line 597 of file qhostinfo.cpp.

◆ setError()

void QHostInfo::setError ( HostInfoError error )

Sets the error type of this QHostInfo to error.

See also: error(), errorString()

Definition at line 642 of file qhostinfo.cpp.

◆ setErrorString()

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(), setError()

Definition at line 688 of file qhostinfo.cpp.

◆ setHostName()

void QHostInfo::setHostName ( const QString & hostName )

Sets the host name of this QHostInfo to hostName.

See also: hostName()

Definition at line 619 of file qhostinfo.cpp.

◆ setLookupId()

void QHostInfo::setLookupId ( int id )

Sets the ID of this lookup to id.

See also: lookupId(), lookupHost()

Definition at line 664 of file qhostinfo.cpp.

◆ swap()

void QHostInfo::swap ( QHostInfo & other )

inlinenoexcept

\memberswap{host-info}

Since: 5.10

Definition at line 35 of file qhostinfo.h.

Friends And Related Symbol Documentation

◆ qt_qhostinfo_lookup

QHostInfo Q_NETWORK_EXPORT qt_qhostinfo_lookup	(	const QString &	name,
		QObject *	receiver,
		const char *	member,
		bool *	valid,
		int *	id )

friend

Definition at line 1057 of file qhostinfo.cpp.

The documentation for this class was generated from the following files:

qtbase/src/network/kernel/qhostinfo.h (674dfdf226542cc33129899df9833847cb6f4629)
qtbase/src/network/kernel/qhostinfo.cpp (3ccb4ce781463f1b8e0cb4c9283b3067fe92a32e)
qtbase/src/network/kernel/qhostinfo_unix.cpp (f0aa391ef89a393221d77d5ad3c1616a4727f11a)
qtbase/src/network/kernel/qnetworkinterface_win.cpp (05fc3aef53348fb58be6308076e000825b704e58)

Public Types

Public Member Functions

Static Public Member Functions

Friends

Detailed Description

Member Enumeration Documentation

◆ HostInfoError

Constructor & Destructor Documentation

◆ QHostInfo() [1/3]

◆ QHostInfo() [2/3]

◆ QHostInfo() [3/3]

◆ ~QHostInfo()

Member Function Documentation

◆ abortHostLookup()

◆ addresses()

◆ error()

◆ errorString()

◆ fromName()

◆ hostName()

◆ localDomainName()

◆ localHostName()

◆ lookupHost() [1/3]

◆ lookupHost() [2/3]

◆ lookupHost() [3/3]

◆ lookupId()

◆ operator=() [1/2]

◆ operator=() [2/2]

◆ setAddresses()

◆ setError()

◆ setErrorString()

◆ setHostName()

◆ setLookupId()

◆ swap()

Friends And Related Symbol Documentation

◆ qt_qhostinfo_lookup