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# QUdpSocket Class Reference
[QtNetwork module]

The QUdpSocket class provides a UDP socket. More...

Inherits QAbstractSocket.

### Types

- enum BindFlag { DefaultForPlatform, ShareAddress, DontShareAddress, ReuseAddressHint }
- class BindMode

### Methods

- __init__ (self, QObject parent = None)
- bool bind (self, QHostAddress, int)
- bool bind (self, int port = 0)
- bool bind (self, QHostAddress, int, BindMode)
- bool bind (self, int, BindMode)
- bool hasPendingDatagrams (self)
- int pendingDatagramSize (self)
- (str, QHostAddress host, int port) readDatagram (self, int maxlen)
- int writeDatagram (self, str, QHostAddress, int)
- int writeDatagram (self, QByteArray, QHostAddress, int)

## Detailed Description

The QUdpSocket class provides a UDP socket.

UDP (User Datagram Protocol) is a lightweight, unreliable, datagram-oriented, connectionless protocol. It can be used when reliability isn't important. QUdpSocket is a subclass of QAbstractSocket that allows you to send and receive UDP datagrams.

The most common way to use this class is to bind to an address and port using bind(), then call writeDatagram() and readDatagram() to transfer data. If you want to use the standard QIODevice functions read(), readLine(), write(), etc., you must first connect the socket directly to a peer by calling connectToHost().

The socket emits the bytesWritten() signal every time a datagram is written to the network. If you just want to send datagrams, you don't need to call bind().

The readyRead() signal is emitted whenever datagrams arrive. In that case, hasPendingDatagrams() returns true. Call pendingDatagramSize() to obtain the size of the first pending datagram, and readDatagram() to read it.

Note: An incoming datagram should be read when you receive the readyRead() signal, otherwise this signal will not be emitted for the next datagram.

Example:

     void Server.initSocket()
     {
         udpSocket = new QUdpSocket(this);
         udpSocket->bind(QHostAddress.LocalHost, 7755);

         connect(udpSocket, SIGNAL(readyRead()),
                 this, SLOT(readPendingDatagrams()));
     }

     void Server.readPendingDatagrams()
     {
         while (udpSocket->hasPendingDatagrams()) {
             QByteArray datagram;
             datagram.resize(udpSocket->pendingDatagramSize());
             QHostAddress sender;
             quint16 senderPort;

             udpSocket->readDatagram(datagram.data(), datagram.size(),
                                     &sender, &senderPort);

             processTheDatagram(datagram);
         }
     }

With QUdpSocket, you can also establish a virtual connection to a UDP server using connectToHost() and then use read() and write() to exchange datagrams without specifying the receiver for each datagram.

The Broadcast Sender and Broadcast Receiver examples illustrate how to use QUdpSocket in applications.

See also QTcpSocket.

## Type Documentation

### QUdpSocket.BindFlag

This enum describes the different flags you can pass to modify the behavior of QUdpSocket.bind().

Note: On Symbian OS bind flags behaviour depends on process capabilties. If process has NetworkControl capability, the bind attempt with ReuseAddressHint will always succeed even if the address and port is already bound by another socket with any flags. If process does not have NetworkControl capability, the bind attempt to address and port already bound by another socket will always fail.

Constant | Value | Description
--- | --- | ---
`QUdpSocket.ShareAddress` | `0x1` | Allow other services to bind to the same address and port. This is useful when multiple processes share the load of a single service by listening to the same address and port (e.g., a web server with several pre-forked listeners can greatly improve response time). However, because any service is allowed to rebind, this option is subject to certain security considerations. Note that by combining this option with ReuseAddressHint, you will also allow your service to rebind an existing shared address. On Unix, this is equivalent to the SO_REUSEADDR socket option. On Windows, this option is ignored.
`QUdpSocket.DontShareAddress` | `0x2` | Bind the address and port exclusively, so that no other services are allowed to rebind. By passing this option to QUdpSocket.bind(), you are guaranteed that on successs, your service is the only one that listens to the address and port. No services are allowed to rebind, even if they pass ReuseAddressHint. This option provides more security than ShareAddress, but on certain operating systems, it requires you to run the server with administrator privileges. On Unix and Mac OS X, not sharing is the default behavior for binding an address and port, so this option is ignored. On Windows, this option uses the SO_EXCLUSIVEADDRUSE socket option.
`QUdpSocket.ReuseAddressHint` | `0x4` | Provides a hint to QUdpSocket that it should try to rebind the service even if the address and port are already bound by another socket. On Windows, this is equivalent to the SO_REUSEADDR socket option. On Unix, this option is ignored.
`QUdpSocket.DefaultForPlatform` | `0x0` | The default option for the current platform. On Unix and Mac OS X, this is equivalent to (DontShareAddress + ReuseAddressHint), and on Windows, its equivalent to ShareAddress.

This enum was introduced in Qt 4.1.

The BindMode type is a typedef for QFlags<BindFlag>. It stores an OR combination of BindFlag values.

## Method Documentation

### QUdpSocket.__init__ (self, QObject parent = None)

The parent argument, if not None, causes self to be owned by Qt instead of PyQt.

Creates a QUdpSocket object.

parent is passed to the QObject constructor.

See also socketType().

### bool QUdpSocket.bind (self, QHostAddress, int)

Binds this socket to the address address and the port port. When bound, the signal readyRead() is emitted whenever a UDP datagram arrives on the specified address and port. This function is useful to write UDP servers.

On success, the functions returns true and the socket enters BoundState; otherwise it returns false.

The socket is bound using the DefaultForPlatform BindMode.

See also readDatagram().

### bool QUdpSocket.bind (self, int port = 0)

This is an overloaded function.

Binds to address on port port, using the BindMode mode.

This function was introduced in Qt 4.1.

### bool QUdpSocket.bind (self, QHostAddress, int, BindMode)

This is an overloaded function.

Binds to QHostAddress:Any on port port.

### bool QUdpSocket.bind (self, int, BindMode)

This is an overloaded function.

Binds to QHostAddress:Any on port port, using the BindMode mode.

This function was introduced in Qt 4.1.

### bool QUdpSocket.hasPendingDatagrams (self)

Returns true if at least one datagram is waiting to be read; otherwise returns false.

See also pendingDatagramSize() and readDatagram().

### int QUdpSocket.pendingDatagramSize (self)

Returns the size of the first pending UDP datagram. If there is no datagram available, this function returns -1.

See also hasPendingDatagrams() and readDatagram().

### (str, QHostAddress host, int port) QUdpSocket.readDatagram (self, int maxlen)

Receives a datagram no larger than maxSize bytes and stores it in data. The sender's host address and port is stored in *address and *port (unless the pointers are 0).

Returns the size of the datagram on success; otherwise returns -1.

If maxSize is too small, the rest of the datagram will be lost. To avoid loss of data, call pendingDatagramSize() to determine the size of the pending datagram before attempting to read it. If maxSize is 0, the datagram will be discarded.

See also writeDatagram(), hasPendingDatagrams(), and pendingDatagramSize().

### int QUdpSocket.writeDatagram (self, str, QHostAddress, int)

Sends the datagram at data of size size to the host address address at port port. Returns the number of bytes sent on success; otherwise returns -1.

Datagrams are always written as one block. The maximum size of a datagram is highly platform-dependent, but can be as low as 8192 bytes. If the datagram is too large, this function will return -1 and error() will return DatagramTooLargeError.

Sending datagrams larger than 512 bytes is in general disadvised, as even if they are sent successfully, they are likely to be fragmented by the IP layer before arriving at their final destination.

Warning: In S60 5.0 and earlier versions, the writeDatagram return value is not reliable for large datagrams.

Warning: Calling this function on a connected UDP socket may result in an error and no packet being sent. If you are using a connected socket, use write() to send datagrams.

See also readDatagram() and write().

### int QUdpSocket.writeDatagram (self, QByteArray, QHostAddress, int)

This is an overloaded function.

Sends the datagram datagram to the host address host and at port port.