QHostInfo Class▲
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Header: QHostInfo
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CMake:
find_package(Qt6 REQUIRED COMPONENTS Network)
target_link_libraries(mytarget PRIVATE Qt6::Network)
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qmake: QT += network
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Group: QHostInfo is part of Network Programming API
Detailed Description▲
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 RFC 6724 there is no guarantee that all IP addresses registered for a domain or host will be returned.
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▲
See also QAbstractSocket, RFC 3492, RFC 6724
Member Type Documentation▲
enum QHostInfo::HostInfoError▲
Member Function Documentation▲
[explicit] QHostInfo::QHostInfo(int id = -1)▲
QHostInfo::QHostInfo(const QHostInfo &other)▲
Constructs a copy of other.
[since 5.14] QHostInfo::QHostInfo(QHostInfo &&other)▲
Move-constructs a new QHostInfo from other.
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.
This function was introduced in Qt 5.14.
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▲
See also lookupHost(), 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▲
See also setAddresses(), hostName(), error()
QHostInfo::HostInfoError QHostInfo::error() const▲
Returns the type of error that occurred if the host name lookup failed; otherwise returns NoError.
See Also▲
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▲
See also setErrorString(), 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▲
See also lookupHost()
QString QHostInfo::hostName() const▲
Returns the name of the host whose IP addresses were looked up.
See Also▲
See also setHostName(), localHostName()
[static] QString QHostInfo::localDomainName()▲
Returns the DNS domain of this machine.
DNS domains are not related to domain names found in Windows networks.
See Also▲
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▲
See also hostName(), 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, &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);There is no guarantee on the order the signals will be emitted if you start multiple requests with lookupHost().
See Also▲
See also abortHostLookup(), addresses(), error(), fromName()
[static, since 5.9] 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.
There is no guarantee on the order the signals will be emitted if you start multiple requests with lookupHost().
This function was introduced in Qt 5.9.
See Also▲
See also abortHostLookup(), addresses(), error(), fromName()
[static, since 5.9] 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.
There is no guarantee on the order the signals will be emitted if you start multiple requests with lookupHost().
This function was introduced in Qt 5.9.
See Also▲
See also abortHostLookup(), addresses(), error(), fromName()
int QHostInfo::lookupId() const▲
void QHostInfo::setAddresses(const QList<QHostAddress> &addresses)▲
void QHostInfo::setError(QHostInfo::HostInfoError error)▲
void QHostInfo::setErrorString(const QString &str)▲
Sets the human readable description of the error that occurred to str if the lookup failed.
See Also▲
See also errorString(), setError()
void QHostInfo::setHostName(const QString &hostName)▲
void QHostInfo::setLookupId(int id)▲
[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.
QHostInfo &QHostInfo::operator=(const QHostInfo &other)▲
Assigns the data of the other object to this host info object, and returns a reference to it.
[since 5.10] QHostInfo &QHostInfo::operator=(QHostInfo &&other)▲
Move-assigns other to this QHostInfo instance.
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.
This function was introduced in Qt 5.10.