QHostInfo Class Reference
[QtNetwork module]

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.

Example:

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

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

The slot is invoked when the results are ready. (If you use Qt for Embedded Linux and disabled multithreading support by defining QT_NO_THREAD, lookupHost() will block until the lookup has finished.) 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.nokia.com");

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.

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. Note: Since Qt 4.6.3 QHostInfo is using a small internal 60 second DNS cache for performance improvements.

See also QAbstractSocket and RFC 3492.

Member Type Documentation

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

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

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

     foreach (QHostAddress address, host.addresses())
         qDebug() << "Found address:" << address.toString();
 }

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