CopperSpice API  1.7.2
QHostInfo Class Reference

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

Public Types

enum  HostInfoError

Public Methods

 QHostInfo (const QHostInfo &other)
 QHostInfo (int id=-1)
 ~QHostInfo ()
QList< QHostAddressaddresses () const
HostInfoError error () const
QString errorString () const
QString hostName () const
int lookupId () const
QHostInfo & operator= (const QHostInfo &other)
void setAddresses (const QList< QHostAddress > &addresses)
void setError (HostInfoError error)
void setErrorString (const QString &errorStr)
void setHostName (const QString &hostName)
void setLookupId (int id)

Static Public Methods

static void abortHostLookup (int id)
static QHostInfo fromName (const QString &name)
static QString localDomainName ()
static QString localHostName ()
static int lookupHost (const QString &name, QObject *receiver, const QString &member)

Detailed Description

The QHostInfo class provides static functions for host name lookups.

QHostInfo uses the lookup mechanisms provided by the operating system to find 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.


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

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("");

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 uss multiple threads for DNS lookup instead of one dedicated DNS thread.

See also
QAbstractSocket, RFC 3492

Member Enumeration Documentation

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

QHostInfo::NoError 0The lookup was successful.
QHostInfo::HostNotFound 1No IP addresses were found for the host.
QHostInfo::UnknownError 2An unknown error occurred.
See also
error(), setError()

Constructor & Destructor Documentation

QHostInfo::QHostInfo ( int  id = -1)

Constructs an empty host info object with lookup ID id.

See also
QHostInfo::QHostInfo ( const QHostInfo &  other)

Copy constructs a new QHostInfo from other.

QHostInfo::~QHostInfo ( )

Destroys the host info object.

Method Documentation

void QHostInfo::abortHostLookup ( int  id)

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

See also
lookupHost(), lookupId()
QList< QHostAddress > QHostInfo::addresses ( ) const

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


QHostInfo info;
if (!info.addresses().isEmpty()) {
QHostAddress address = info.addresses().first();
// use the first IP address
See also
setAddresses(), hostName(), error()
HostInfoError QHostInfo::error ( ) const

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

See also
setError(), 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()
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
QString QHostInfo::hostName ( ) const

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

See also
setHostName(), localHostName()
QString QHostInfo::localDomainName ( )

Returns the DNS domain of this machine.

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

See also
QString QHostInfo::localHostName ( )

Returns the host name of this machine.

See also
int QHostInfo::lookupHost ( const QString name,
QObject receiver,
const QString 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("", 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();
for (const QHostAddress &address : host.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("", this, SLOT(lookedUp(QHostInfo)));
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()
int QHostInfo::lookupId ( ) const

Returns the ID of this lookup.

See also
setLookupId(), abortHostLookup(), hostName()
QHostInfo & QHostInfo::operator= ( const QHostInfo &  other)

Copy assigns from other and returns a reference to this object.

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

Sets the list of addresses in this QHostInfo to addresses.

See also
void QHostInfo::setError ( HostInfoError  error)

Sets the error type of this QHostInfo to error.

See also
error(), errorString()
void QHostInfo::setErrorString ( const QString errorStr)

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

See also
errorString(), setError()
void QHostInfo::setHostName ( const QString hostName)

Sets the host name of this QHostInfo to hostname.

See also
void QHostInfo::setLookupId ( int  id)

Sets the ID of this lookup to id.

See also
lookupId(), lookupHost()