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# QHostInfo Class Reference
[QtNetwork module]

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

### Types

- enum HostInfoError { NoError, HostNotFound, UnknownError }

### Methods

- __init__ (self, int id = -1)
- __init__ (self, QHostInfo d)
- list-of-QHostAddress addresses (self)
- HostInfoError error (self)
- QString errorString (self)
- QString hostName (self)
- int lookupId (self)
- setAddresses (self, list-of-QHostAddress addresses)
- setError (self, HostInfoError error)
- setErrorString (self, QString errorString)
- setHostName (self, QString name)
- setLookupId (self, int id)

### Static Methods

- abortHostLookup (int lookupId)
- QHostInfo fromName (QString name)
- QString localDomainName ()
- QString localHostName ()
- int lookupHost (QString name, QObject receiver, SLOT(QHostInfo)SLOT() member)
- int lookupHost (QString name, callable receiver)

## 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.

## Type Documentation

### QHostInfo.HostInfoError

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

Constant | Value | Description
--- | --- | ---
`QHostInfo.NoError` | `0` | The lookup was successful.
`QHostInfo.HostNotFound` | `1` | No IP addresses were found for the host.
`QHostInfo.UnknownError` | `2` | An unknown error occurred.

See also error() and setError().

## Method Documentation

### QHostInfo.__init__ (self, int id = -1)

Constructs an empty host info object with lookup ID id.

See also lookupId().

### QHostInfo.__init__ (self, QHostInfo d)

Constructs a copy of other.

### QHostInfo.abortHostLookup (int lookupId)

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

See also lookupHost() and lookupId().

### list-of-QHostAddress QHostInfo.addresses (self)

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().

### HostInfoError QHostInfo.error (self)

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

See also setError() and errorString().

### QString QHostInfo.errorString (self)

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

See also setErrorString() and error().

### QHostInfo QHostInfo.fromName (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 (self)

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

See also setHostName() and 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 hostName().

### QString QHostInfo.localHostName ()

Returns the host name of this machine.

See also hostName().

### int QHostInfo.lookupHost (QString name, QObject receiver, SLOT(QHostInfo)SLOT() 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;
         }

         foreach (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("4.2.2.1",
                           this, SLOT(lookedUp(QHostInfo)));

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(), and fromName().

### int QHostInfo.lookupHost (QString name, callable receiver)

### int QHostInfo.lookupId (self)

Returns the ID of this lookup.

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

### QHostInfo.setAddresses (self, list-of-QHostAddress addresses)

Sets the list of addresses in this QHostInfo to addresses.

See also addresses().

### QHostInfo.setError (self, HostInfoError error)

Sets the error type of this QHostInfo to error.

See also error() and errorString().

### QHostInfo.setErrorString (self, QString errorString)

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

See also errorString() and setError().

### QHostInfo.setHostName (self, QString name)

Sets the host name of this QHostInfo to hostName.

See also hostName().

### QHostInfo.setLookupId (self, int id)

Sets the ID of this lookup to id.

See also lookupId() and lookupHost().