Qabstractsocket error occurred

The QAbstractSocket class provides the base functionality common to all socket types.
More…

#include <qabstractsocket.h>

Public Types
enum	NetworkLayerProtocol { IPv4Protocol, IPv6Protocol, UnknownNetworkLayerProtocol = -1 }
	This enum describes the network layer protocol values used in Qt. More…
enum	SocketError {   ConnectionRefusedError, RemoteHostClosedError, HostNotFoundError, SocketAccessError,   SocketResourceError, SocketTimeoutError, DatagramTooLargeError, NetworkError,   AddressInUseError, SocketAddressNotAvailableError, UnsupportedSocketOperationError, UnfinishedSocketOperationError,   ProxyAuthenticationRequiredError, SslHandshakeFailedError, ProxyConnectionRefusedError, ProxyConnectionClosedError,   ProxyConnectionTimeoutError, ProxyNotFoundError, ProxyProtocolError, UnknownSocketError = -1 }
	This enum describes the socket errors that can occur. More…
enum	SocketOption { LowDelayOption, KeepAliveOption, MulticastTtlOption, MulticastLoopbackOption }
	This enum represents the options that can be set on a socket. More…
enum	SocketState {   UnconnectedState, HostLookupState, ConnectingState, ConnectedState,   BoundState, ListeningState, ClosingState }
	This enum describes the different states in which a socket can be. More…
enum	SocketType { TcpSocket, UdpSocket, UnknownSocketType = -1 }
	This enum describes the transport layer protocol. More…
Public Types inherited from QIODevice
enum	OpenModeFlag {   NotOpen = 0x0000, ReadOnly = 0x0001, WriteOnly = 0x0002, ReadWrite = ReadOnly | WriteOnly,   Append = 0x0004, Truncate = 0x0008, Text = 0x0010, Unbuffered = 0x0020 }
	This enum is used with open() to describe the mode in which a device is opened. More…

Signals
void	connected ()
	This signal is emitted after connectToHost() has been called and a connection has been successfully established. More…
void	disconnected ()
	This signal is emitted when the socket has been disconnected. More…
void	error (QAbstractSocket::SocketError)
	This signal is emitted after an error occurred. More…
void	hostFound ()
	This signal is emitted after connectToHost() has been called and the host lookup has succeeded. More…
void	proxyAuthenticationRequired (const QNetworkProxy &proxy, QAuthenticator *authenticator)
void	stateChanged (QAbstractSocket::SocketState)
	This signal is emitted whenever QAbstractSocket’s state changes. More…
Signals inherited from QIODevice
void	aboutToClose ()
	This signal is emitted when the device is about to close. More…
void	bytesWritten (qint64 bytes)
	This signal is emitted every time a payload of data has been written to the device. More…
void	readChannelFinished ()
	This signal is emitted when the input (reading) stream is closed in this device. More…
void	readyRead ()
	This signal is emitted once every time new data is available for reading from the device. More…
Signals inherited from QObject
void	destroyed (QObject *=0)
	This signal is emitted immediately before the object obj is destroyed, and can not be blocked. More…

Public Functions
void	abort ()
	Aborts the current connection and resets the socket. More…
bool	atEnd () const
	Returns true if no more data is currently available for reading; otherwise returns false. More…
qint64	bytesAvailable () const
	Returns the number of incoming bytes that are waiting to be read. More…
qint64	bytesToWrite () const
	Returns the number of bytes that are waiting to be written. More…
bool	canReadLine () const
	Returns true if a line of data can be read from the socket; otherwise returns false. More…
void	close ()
	Closes the I/O device for the socket, disconnects the socket’s connection with the host, closes the socket, and resets the name, address, port number and underlying socket descriptor. More…
void	connectToHost (const QString &hostName, quint16 port, OpenMode mode=ReadWrite)
	Attempts to make a connection to hostName on the given port. More…
void	connectToHost (const QHostAddress &address, quint16 port, OpenMode mode=ReadWrite)
	Attempts to make a connection to address on port port. More…
void	disconnectFromHost ()
	Attempts to close the socket. More…
SocketError	error () const
	Returns the type of error that last occurred. More…
bool	flush ()
	This function writes as much as possible from the internal write buffer to the underlying network socket, without blocking. More…
bool	isSequential () const
	Reimplemented Function More…
bool	isValid () const
	Returns true if the socket is valid and ready for use; otherwise returns false. More…
QHostAddress	localAddress () const
	Returns the host address of the local socket if available; otherwise returns QHostAddress::Null. More…
quint16	localPort () const
	Returns the host port number (in native byte order) of the local socket if available; otherwise returns 0. More…
QHostAddress	peerAddress () const
	Returns the address of the connected peer if the socket is in ConnectedState; otherwise returns QHostAddress::Null. More…
QString	peerName () const
	Returns the name of the peer as specified by connectToHost(), or an empty QString if connectToHost() has not been called. More…
quint16	peerPort () const
	Returns the port of the connected peer if the socket is in ConnectedState; otherwise returns 0. More…
QNetworkProxy	proxy () const
	Returns the network proxy for this socket. More…
	QAbstractSocket (SocketType socketType, QObject *parent)
	Creates a new abstract socket of type socketType. More…
qint64	readBufferSize () const
	Returns the size of the internal read buffer. More…
void	setProxy (const QNetworkProxy &networkProxy)
	Sets the explicit network proxy for this socket to networkProxy. More…
void	setReadBufferSize (qint64 size)
	Sets the size of QAbstractSocket’s internal read buffer to be size bytes. More…
bool	setSocketDescriptor (int socketDescriptor, SocketState state=ConnectedState, OpenMode openMode=ReadWrite)
	Initializes QAbstractSocket with the native socket descriptor socketDescriptor. More…
void	setSocketOption (QAbstractSocket::SocketOption option, const QVariant &value)
	Sets the given option to the value described by value. More…
int	socketDescriptor () const
	Returns the native socket descriptor of the QAbstractSocket object if this is available; otherwise returns -1. More…
QVariant	socketOption (QAbstractSocket::SocketOption option)
	Returns the value of the option option. More…
SocketType	socketType () const
	Returns the socket type (TCP, UDP, or other). More…
SocketState	state () const
	Returns the state of the socket. More…
bool	waitForBytesWritten (int msecs=30000)
	Reimplemented Function More…
bool	waitForConnected (int msecs=30000)
	Waits until the socket is connected, up to msecs milliseconds. More…
bool	waitForDisconnected (int msecs=30000)
	Waits until the socket has disconnected, up to msecs milliseconds. More…
bool	waitForReadyRead (int msecs=30000)
	This function blocks until new data is available for reading and the QIODevice::readyRead() signal has been emitted. More…
virtual	~QAbstractSocket ()
	Destroys the socket. More…
Public Functions inherited from QIODevice
QString	errorString () const
	Returns a human-readable description of the last device error that occurred. More…
bool	getChar (char *c)
	Reads one character from the device and stores it in c. More…
bool	isOpen () const
	Returns true if the device is open; otherwise returns false. More…
bool	isReadable () const
	Returns true if data can be read from the device; otherwise returns false. More…
bool	isTextModeEnabled () const
	Returns true if the Text flag is enabled; otherwise returns false. More…
bool	isWritable () const
	Returns true if data can be written to the device; otherwise returns false. More…
virtual bool	open (OpenMode mode)
	Opens the device and sets its OpenMode to mode. More…
OpenMode	openMode () const
	Returns the mode in which the device has been opened; i.e. More…
qint64	peek (char *data, qint64 maxlen)
	Reads at most maxSize bytes from the device into data, without side effects (i. More…
QByteArray	peek (qint64 maxlen)
	Peeks at most maxSize bytes from the device, returning the data peeked as a QByteArray. More…
virtual qint64	pos () const
	For random-access devices, this function returns the position that data is written to or read from. More…
bool	putChar (char c)
	Writes the character c to the device. More…
	QIODevice ()
	Constructs a QIODevice object. More…
	QIODevice (QObject *parent)
	Constructs a QIODevice object with the given parent. More…
qint64	read (char *data, qint64 maxlen)
	Reads at most maxSize bytes from the device into data, and returns the number of bytes read. More…
QByteArray	read (qint64 maxlen)
	Reads at most maxSize bytes from the device, and returns the data read as a QByteArray. More…
QByteArray	readAll ()
	Reads all available data from the device, and returns it as a QByteArray. More…
qint64	readLine (char *data, qint64 maxlen)
	This function reads a line of ASCII characters from the device, up to a maximum of maxSize — 1 bytes, stores the characters in data, and returns the number of bytes read. More…
QByteArray	readLine (qint64 maxlen=0)
	Reads a line from the device, but no more than maxSize characters, and returns the result as a QByteArray. More…
virtual bool	reset ()
	Seeks to the start of input for random-access devices. More…
virtual bool	seek (qint64 pos)
	For random-access devices, this function sets the current position to pos, returning true on success, or false if an error occurred. More…
void	setTextModeEnabled (bool enabled)
	If enabled is true, this function sets the Text flag on the device; otherwise the Text flag is removed. More…
virtual qint64	size () const
	For open random-access devices, this function returns the size of the device. More…
void	ungetChar (char c)
	Puts the character c back into the device, and decrements the current position unless the position is 0. More…
qint64	write (const char *data, qint64 len)
	Writes at most maxSize bytes of data from data to the device. More…
qint64	write (const char *data)
	Writes data from a zero-terminated string of 8-bit characters to the device. More…
qint64	write (const QByteArray &data)
	Writes the content of byteArray to the device. More…
virtual	~QIODevice ()
	The destructor is virtual, and QIODevice is an abstract base class. More…
Public Functions inherited from QObject
bool	blockSignals (bool b)
	If block is true, signals emitted by this object are blocked (i.e., emitting a signal will not invoke anything connected to it). More…
const QObjectList &	children () const
	Returns a list of child objects. More…
bool	connect (const QObject *sender, const char *signal, const char *member, Qt::ConnectionType type=Qt::AutoConnection) const
bool	disconnect (const char *signal=0, const QObject *receiver=0, const char *member=0)
bool	disconnect (const QObject *receiver, const char *member=0)
void	dumpObjectInfo ()
	Dumps information about signal connections, etc. More…
void	dumpObjectTree ()
	Dumps a tree of children to the debug output. More…
QList< QByteArray >	dynamicPropertyNames () const
	Returns the names of all properties that were dynamically added to the object using setProperty(). More…
virtual bool	event (QEvent *)
	This virtual function receives events to an object and should return true if the event e was recognized and processed. More…
virtual bool	eventFilter (QObject *, QEvent *)
	Filters events if this object has been installed as an event filter for the watched object. More…
template<typename T >
T	findChild (const QString &aName=QString()) const
	Returns the child of this object that can be cast into type T and that is called name, or 0 if there is no such object. More…
template<typename T >
QList< T >	findChildren (const QString &aName=QString()) const
	Returns all children of this object with the given name that can be cast to type T, or an empty list if there are no such objects. More…
template<typename T >
QList< T >	findChildren (const QRegExp &re) const
bool	inherits (const char *classname) const
	Returns true if this object is an instance of a class that inherits className or a QObject subclass that inherits className; otherwise returns false. More…
void	installEventFilter (QObject *)
	Installs an event filter filterObj on this object. More…
bool	isWidgetType () const
	Returns true if the object is a widget; otherwise returns false. More…
void	killTimer (int id)
	Kills the timer with timer identifier, id. More…
virtual const QMetaObject *	metaObject () const
	Returns a pointer to the meta-object of this object. More…
void	moveToThread (QThread *thread)
	Changes the thread affinity for this object and its children. More…
QString	objectName () const
QObject *	parent () const
	Returns a pointer to the parent object. More…
QVariant	property (const char *name) const
	Returns the value of the object’s name property. More…
Q_INVOKABLE	QObject (QObject *parent=0)
	Constructs an object with parent object parent. More…
void	removeEventFilter (QObject *)
	Removes an event filter object obj from this object. More…
void	setObjectName (const QString &name)
void	setParent (QObject *)
	Makes the object a child of parent. More…
bool	setProperty (const char *name, const QVariant &value)
	Sets the value of the object’s name property to value. More…
void	setUserData (uint id, QObjectUserData *data)
bool	signalsBlocked () const
	Returns true if signals are blocked; otherwise returns false. More…
int	startTimer (int interval)
	Starts a timer and returns a timer identifier, or returns zero if it could not start a timer. More…
QThread *	thread () const
	Returns the thread in which the object lives. More…
QObjectUserData *	userData (uint id) const
virtual	~QObject ()
	Destroys the object, deleting all its child objects. More…

Protected Functions
	QAbstractSocket (SocketType socketType, QAbstractSocketPrivate &dd, QObject *parent=0)
	Constructs a new abstract socket of type socketType. More…
qint64	readData (char *data, qint64 maxlen)
	Reimplemented Function More…
qint64	readLineData (char *data, qint64 maxlen)
	Reimplemented Function More…
void	setLocalAddress (const QHostAddress &address)
	Sets the address on the local side of a connection to address. More…
void	setLocalPort (quint16 port)
	Sets the port on the local side of a connection to port. More…
void	setPeerAddress (const QHostAddress &address)
	Sets the address of the remote side of the connection to address. More…
void	setPeerName (const QString &name)
	Sets the host name of the remote peer to name. More…
void	setPeerPort (quint16 port)
	Sets the port of the remote side of the connection to port. More…
void	setSocketError (SocketError socketError)
	Sets the type of error that last occurred to socketError. More…
void	setSocketState (SocketState state)
	Sets the state of the socket to state. More…
qint64	writeData (const char *data, qint64 len)
	Reimplemented Function More…
Protected Functions inherited from QIODevice
	QIODevice (QIODevicePrivate &dd, QObject *parent=0)
void	setErrorString (const QString &errorString)
	Sets the human readable description of the last device error that occurred to str. More…
void	setOpenMode (OpenMode openMode)
	Sets the OpenMode of the device to openMode. More…
Protected Functions inherited from QObject
virtual void	childEvent (QChildEvent *)
	This event handler can be reimplemented in a subclass to receive child events. More…
virtual void	connectNotify (const char *signal)
	This virtual function is called when something has been connected to signal in this object. More…
virtual void	customEvent (QEvent *)
	This event handler can be reimplemented in a subclass to receive custom events. More…
virtual void	disconnectNotify (const char *signal)
	This virtual function is called when something has been disconnected from signal in this object. More…
	QObject (QObjectPrivate &dd, QObject *parent=0)
int	receivers (const char *signal) const
	Returns the number of receivers connected to the signal. More…
QObject *	sender () const
	Returns a pointer to the object that sent the signal, if called in a slot activated by a signal; otherwise it returns 0. More…
int	senderSignalIndex () const
virtual void	timerEvent (QTimerEvent *)
	This event handler can be reimplemented in a subclass to receive timer events for the object. More…

Additional Inherited Members
Public Slots inherited from QObject
void	deleteLater ()
	Schedules this object for deletion. More…
Static Public Functions inherited from QObject
static bool	connect (const QObject *sender, const char *signal, const QObject *receiver, const char *member, Qt::ConnectionType=Qt::AutoConnection)
	Creates a connection of the given type from the signal in the sender object to the method in the receiver object. More…
static bool	connect (const QObject *sender, const QMetaMethod &signal, const QObject *receiver, const QMetaMethod &method, Qt::ConnectionType type=Qt::AutoConnection)
static bool	disconnect (const QObject *sender, const char *signal, const QObject *receiver, const char *member)
	Disconnects signal in object sender from method in object receiver. More…
static bool	disconnect (const QObject *sender, const QMetaMethod &signal, const QObject *receiver, const QMetaMethod &member)
static uint	registerUserData ()
static QString	tr (const char *sourceText, const char *comment=0, int n=-1)
static QString	trUtf8 (const char *sourceText, const char *comment=0, int n=-1)
Static Public Variables inherited from QObject
static const QMetaObject	staticMetaObject
	This variable stores the meta-object for the class. More…
Protected Variables inherited from QObject
QScopedPointer< QObjectData >	d_ptr
Static Protected Variables inherited from QObject
static const QMetaObject	staticQtMetaObject
Related Functions inherited from QObject
T	qFindChildqFindChildren (const QObject *obj, const QString &name)()
QList< T >	qFindChildrenqFindChildren (const QObject *obj, const QString &name)()
QList< T >	qFindChildrenqFindChildren (const QObject *obj, const QRegExp &regExp)()
T *	qobject_cast (QObject *object)
	QObjectList
void *	qt_find_obj_child (QObject *parent, const char *type, const QString &name)
	Returns a pointer to the object named name that inherits type and with a given parent. More…

◆ NetworkLayerProtocol

◆ SocketError

◆ SocketOption

◆ SocketState

◆ SocketType

◆ ~QAbstractSocket()

◆ QAbstractSocket() [2/2]

◆ abort()

◆ atEnd()

 // This slot is connected to QAbstractSocket::readyRead()
 void SocketClass::readyReadSlot()
 {
     while (!socket.atEnd()) {
         QByteArray data = socket.read(100);
         ....
     }
 }

◆ bytesAvailable()

◆ bytesToWrite()

◆ canReadLine()

◆ close()

◆ connected

◆ connectToHost() [1/2]

◆ connectToHost() [2/2]

◆ connectToHostImplementation

◆ disconnected

◆ disconnectFromHost()

◆ disconnectFromHostImplementation

◆ error() [1/2]

◆ error [2/2]

◆ flush()

◆ hostFound

◆ isSequential()

◆ isValid()

◆ localAddress()

◆ localPort()

◆ peerAddress()

◆ peerName()

◆ peerPort()

◆ proxy()

◆ proxyAuthenticationRequired

◆ readBufferSize()

◆ readData()

◆ readLineData()

◆ setLocalAddress()

◆ setLocalPort()

◆ setPeerAddress()

◆ setPeerName()

◆ setPeerPort()

◆ setProxy()

◆ setReadBufferSize()

◆ setSocketDescriptor()

◆ setSocketError()

◆ setSocketOption()

◆ setSocketState()

◆ socketDescriptor()

◆ socketOption()

◆ socketType()

◆ state()

◆ stateChanged

◆ waitForBytesWritten()

◆ waitForConnected()

◆ waitForDisconnected()

◆ waitForReadyRead()

◆ writeData()

The documentation for this class was generated from the following files:

• /src/network/socket/qabstractsocket.h
• /src/network/socket/qabstractsocket.cpp

The QAbstractSocket class provides the base functionality common to all socket types. More…

• List of all members, including inherited members

Note: All functions in this class are reentrant.

Public Types

Public Functions

Reimplemented Public Functions

Signals

Protected Functions

Reimplemented Protected Functions

Detailed Description

QAbstractSocket is the base class for QTcpSocket and QUdpSocket and contains all common functionality of these two classes. If you need a socket, you have two options:

• Instantiate QTcpSocket or QUdpSocket.
• Create a native socket descriptor, instantiate QAbstractSocket, and call setSocketDescriptor() to wrap the native socket.

TCP (Transmission Control Protocol) is a reliable, stream-oriented, connection-oriented transport protocol. UDP (User Datagram Protocol) is an unreliable, datagram-oriented, connectionless protocol. In practice, this means that TCP is better suited for continuous transmission of data, whereas the more lightweight UDP can be used when reliability isn’t important.

QAbstractSocket’s API unifies most of the differences between the two protocols. For example, although UDP is connectionless, connectToHost() establishes a virtual connection for UDP sockets, enabling you to use QAbstractSocket in more or less the same way regardless of the underlying protocol. Internally, QAbstractSocket remembers the address and port passed to connectToHost(), and functions like read() and write() use these values.

At any time, QAbstractSocket has a state (returned by state()). The initial state is UnconnectedState. After calling connectToHost(), the socket first enters HostLookupState. If the host is found, QAbstractSocket enters ConnectingState and emits the hostFound() signal. When the connection has been established, it enters ConnectedState and emits connected(). If an error occurs at any stage, errorOccurred() is emitted. Whenever the state changes, stateChanged() is emitted. For convenience, isValid() returns true if the socket is ready for reading and writing, but note that the socket’s state must be ConnectedState before reading and writing can occur.

Read or write data by calling read() or write(), or use the convenience functions readLine() and readAll(). QAbstractSocket also inherits getChar(), putChar(), and ungetChar() from QIODevice, which work on single bytes. The bytesWritten() signal is emitted when data has been written to the socket. Note that Qt does not limit the write buffer size. You can monitor its size by listening to this signal.

The readyRead() signal is emitted every time a new chunk of data has arrived. bytesAvailable() then returns the number of bytes that are available for reading. Typically, you would connect the readyRead() signal to a slot and read all available data there. If you don’t read all the data at once, the remaining data will still be available later, and any new incoming data will be appended to QAbstractSocket’s internal read buffer. To limit the size of the read buffer, call setReadBufferSize().

To close the socket, call disconnectFromHost(). QAbstractSocket enters QAbstractSocket::ClosingState. After all pending data has been written to the socket, QAbstractSocket actually closes the socket, enters QAbstractSocket::UnconnectedState, and emits disconnected(). If you want to abort a connection immediately, discarding all pending data, call abort() instead. If the remote host closes the connection, QAbstractSocket will emit errorOccurred(QAbstractSocket::RemoteHostClosedError), during which the socket state will still be ConnectedState, and then the disconnected() signal will be emitted.

The port and address of the connected peer is fetched by calling peerPort() and peerAddress(). peerName() returns the host name of the peer, as passed to connectToHost(). localPort() and localAddress() return the port and address of the local socket.

QAbstractSocket provides a set of functions that suspend the calling thread until certain signals are emitted. These functions can be used to implement blocking sockets:

• waitForConnected() blocks until a connection has been established.
• waitForReadyRead() blocks until new data is available for reading.
• waitForBytesWritten() blocks until one payload of data has been written to the socket.
• waitForDisconnected() blocks until the connection has closed.

We show an example:

    int numRead = 0, numReadTotal = 0;
    char buffer[50];

    forever {
        numRead  = socket.read(buffer, 50);

        // do whatever with array

        numReadTotal += numRead;
        if (numRead == 0 && !socket.waitForReadyRead())
            break;
    }

If waitForReadyRead() returns false, the connection has been closed or an error has occurred.

Programming with a blocking socket is radically different from programming with a non-blocking socket. A blocking socket doesn’t require an event loop and typically leads to simpler code. However, in a GUI application, blocking sockets should only be used in non-GUI threads, to avoid freezing the user interface. See the fortuneclient and blockingfortuneclient examples for an overview of both approaches.

Note: We discourage the use of the blocking functions together with signals. One of the two possibilities should be used.

QAbstractSocket can be used with QTextStream and QDataStream’s stream operators (operator<<() and operator>>()). There is one issue to be aware of, though: You must make sure that enough data is available before attempting to read it using operator>>().

See also QNetworkAccessManager and QTcpServer.

Member Type Documentation

[since 5.0] enum QAbstractSocket::BindFlagflags QAbstractSocket::BindMode

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

This enum was introduced or modified in Qt 5.0.

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

enum QAbstractSocket::NetworkLayerProtocol

This enum describes the network layer protocol values used in Qt.

See also QHostAddress::protocol().

[since 5.0] enum QAbstractSocket::PauseModeflags QAbstractSocket::PauseModes

This enum describes the behavior of when the socket should hold back with continuing data transfer. The only notification currently supported is QSslSocket::sslErrors().

This enum was introduced or modified in Qt 5.0.

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

enum QAbstractSocket::SocketError

This enum describes the socket errors that can occur.

See also QAbstractSocket::error() and QAbstractSocket::errorOccurred().

enum QAbstractSocket::SocketOption

This enum represents the options that can be set on a socket. If desired, they can be set after having received the connected() signal from the socket or after having received a new socket from a QTcpServer.

Possible values for TypeOfServiceOption are:

See also QAbstractSocket::setSocketOption() and QAbstractSocket::socketOption().

enum QAbstractSocket::SocketState

This enum describes the different states in which a socket can be.

See also QAbstractSocket::state().

enum QAbstractSocket::SocketType

This enum describes the transport layer protocol.

See also QAbstractSocket::socketType().

Member Function Documentation

QAbstractSocket::QAbstractSocket(QAbstractSocket::SocketType socketType, QObject *parent)

Creates a new abstract socket of type socketType. The parent argument is passed to QObject’s constructor.

See also socketType(), QTcpSocket, and QUdpSocket.

[signal] void QAbstractSocket::connected()

This signal is emitted after connectToHost() has been called and a connection has been successfully established.

Note: On some operating systems the connected() signal may be directly emitted from the connectToHost() call for connections to the localhost.

See also connectToHost() and disconnected().

[signal] void QAbstractSocket::disconnected()

This signal is emitted when the socket has been disconnected.

Warning: If you need to delete the sender() of this signal in a slot connected to it, use the deleteLater() function.

See also connectToHost(), disconnectFromHost(), and abort().

[signal, since 5.15] void QAbstractSocket::errorOccurred(QAbstractSocket::SocketError socketError)

This signal is emitted after an error occurred. The socketError parameter describes the type of error that occurred.

When this signal is emitted, the socket may not be ready for a reconnect attempt. In that case, attempts to reconnect should be done from the event loop. For example, use a QTimer::singleShot() with 0 as the timeout.

QAbstractSocket::SocketError is not a registered metatype, so for queued connections, you will have to register it with Q_DECLARE_METATYPE() and qRegisterMetaType().

This function was introduced in Qt 5.15.

See also error(), errorString(), and Creating Custom Qt Types.

[signal] void QAbstractSocket::hostFound()

This signal is emitted after connectToHost() has been called and the host lookup has succeeded.

Note: Since Qt 4.6.3 QAbstractSocket may emit hostFound() directly from the connectToHost() call since a DNS result could have been cached.

See also connected().

[signal] void QAbstractSocket::proxyAuthenticationRequired(const QNetworkProxy &proxy, QAuthenticator *authenticator)

This signal can be emitted when a proxy that requires authentication is used. The authenticator object can then be filled in with the required details to allow authentication and continue the connection.

Note: It is not possible to use a QueuedConnection to connect to this signal, as the connection will fail if the authenticator has not been filled in with new information when the signal returns.

See also QAuthenticator and QNetworkProxy.

[signal] void QAbstractSocket::stateChanged(QAbstractSocket::SocketState socketState)

This signal is emitted whenever QAbstractSocket’s state changes. The socketState parameter is the new state.

QAbstractSocket::SocketState is not a registered metatype, so for queued connections, you will have to register it with Q_DECLARE_METATYPE() and qRegisterMetaType().

See also state() and Creating Custom Qt Types.

[virtual] QAbstractSocket::~QAbstractSocket()

Destroys the socket.

void QAbstractSocket::abort()

Aborts the current connection and resets the socket. Unlike disconnectFromHost(), this function immediately closes the socket, discarding any pending data in the write buffer.

See also disconnectFromHost() and close().

[virtual, since 5.0] bool QAbstractSocket::bind(const QHostAddress &address, quint16 port = 0, QAbstractSocket::BindMode mode = DefaultForPlatform)

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

For UDP sockets, after binding, the signal QUdpSocket::readyRead() is emitted whenever a UDP datagram arrives on the specified address and port. Thus, this function is useful to write UDP servers.

For TCP sockets, this function may be used to specify which interface to use for an outgoing connection, which is useful in case of multiple network interfaces.

By default, the socket is bound using the DefaultForPlatform BindMode. If a port is not specified, a random port is chosen.

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

This function was introduced in Qt 5.0.

[since 5.0] bool QAbstractSocket::bind(quint16 port = 0, QAbstractSocket::BindMode mode = DefaultForPlatform)

This is an overloaded function.

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

By default, the socket is bound using the DefaultForPlatform BindMode. If a port is not specified, a random port is chosen.

This function was introduced in Qt 5.0.

[override virtual] qint64 QAbstractSocket::bytesAvailable() const

Reimplements: QIODevice::bytesAvailable() const.

Returns the number of incoming bytes that are waiting to be read.

See also bytesToWrite() and read().

[override virtual] qint64 QAbstractSocket::bytesToWrite() const

Reimplements: QIODevice::bytesToWrite() const.

Returns the number of bytes that are waiting to be written. The bytes are written when control goes back to the event loop or when flush() is called.

See also bytesAvailable() and flush().

[override virtual] void QAbstractSocket::close()

Reimplements: QIODevice::close().

Closes the I/O device for the socket and calls disconnectFromHost() to close the socket’s connection.

See QIODevice::close() for a description of the actions that occur when an I/O device is closed.

See also abort().

[virtual] void QAbstractSocket::connectToHost(const QString &hostName, quint16 port, QIODeviceBase::OpenMode openMode = ReadWrite, QAbstractSocket::NetworkLayerProtocol protocol = AnyIPProtocol)

Attempts to make a connection to hostName on the given port. The protocol parameter can be used to specify which network protocol to use (eg. IPv4 or IPv6).

The socket is opened in the given openMode and first enters HostLookupState, then performs a host name lookup of hostName. If the lookup succeeds, hostFound() is emitted and QAbstractSocket enters ConnectingState. It then attempts to connect to the address or addresses returned by the lookup. Finally, if a connection is established, QAbstractSocket enters ConnectedState and emits connected().

At any point, the socket can emit errorOccurred() to signal that an error occurred.

hostName may be an IP address in string form (e.g., «43.195.83.32»), or it may be a host name (e.g., «example.com»). QAbstractSocket will do a lookup only if required. port is in native byte order.

See also state(), peerName(), peerAddress(), peerPort(), and waitForConnected().

void QAbstractSocket::connectToHost(const QHostAddress &address, quint16 port, QIODeviceBase::OpenMode openMode = ReadWrite)

This is an overloaded function.

Attempts to make a connection to address on port port.

[virtual] void QAbstractSocket::disconnectFromHost()

Attempts to close the socket. If there is pending data waiting to be written, QAbstractSocket will enter ClosingState and wait until all data has been written. Eventually, it will enter UnconnectedState and emit the disconnected() signal.

See also connectToHost().

QAbstractSocket::SocketError QAbstractSocket::error() const

Returns the type of error that last occurred.

See also state() and errorString().

bool QAbstractSocket::flush()

This function writes as much as possible from the internal write buffer to the underlying network socket, without blocking. If any data was written, this function returns true; otherwise false is returned.

Call this function if you need QAbstractSocket to start sending buffered data immediately. The number of bytes successfully written depends on the operating system. In most cases, you do not need to call this function, because QAbstractSocket will start sending data automatically once control goes back to the event loop. In the absence of an event loop, call waitForBytesWritten() instead.

See also write() and waitForBytesWritten().

[override virtual] bool QAbstractSocket::isSequential() const

Reimplements: QIODevice::isSequential() const.

bool QAbstractSocket::isValid() const

Returns true if the socket is valid and ready for use; otherwise returns false.

Note: The socket’s state must be ConnectedState before reading and writing can occur.

See also state().

QHostAddress QAbstractSocket::localAddress() const

Returns the host address of the local socket if available; otherwise returns QHostAddress::Null.

This is normally the main IP address of the host, but can be QHostAddress::LocalHost (127.0.0.1) for connections to the local host.

See also localPort(), peerAddress(), and setLocalAddress().

quint16 QAbstractSocket::localPort() const

Returns the host port number (in native byte order) of the local socket if available; otherwise returns 0.

See also localAddress(), peerPort(), and setLocalPort().

[since 5.0] QAbstractSocket::PauseModes QAbstractSocket::pauseMode() const

Returns the pause mode of this socket.

This function was introduced in Qt 5.0.

See also setPauseMode() and resume().

QHostAddress QAbstractSocket::peerAddress() const

Returns the address of the connected peer if the socket is in ConnectedState; otherwise returns QHostAddress::Null.

See also peerName(), peerPort(), localAddress(), and setPeerAddress().

QString QAbstractSocket::peerName() const

Returns the name of the peer as specified by connectToHost(), or an empty QString if connectToHost() has not been called.

See also peerAddress(), peerPort(), and setPeerName().

quint16 QAbstractSocket::peerPort() const

Returns the port of the connected peer if the socket is in ConnectedState; otherwise returns 0.

See also peerAddress(), localPort(), and setPeerPort().

[since 5.13] QString QAbstractSocket::protocolTag() const

Returns the protocol tag for this socket. If the protocol tag is set then this is passed to QNetworkProxyQuery when this is created internally to indicate the protocol tag to be used.

This function was introduced in Qt 5.13.

See also setProtocolTag() and QNetworkProxyQuery.

QNetworkProxy QAbstractSocket::proxy() const

Returns the network proxy for this socket. By default QNetworkProxy::DefaultProxy is used, which means this socket will query the default proxy settings for the application.

See also setProxy(), QNetworkProxy, and QNetworkProxyFactory.

qint64 QAbstractSocket::readBufferSize() const

Returns the size of the internal read buffer. This limits the amount of data that the client can receive before you call read() or readAll().

A read buffer size of 0 (the default) means that the buffer has no size limit, ensuring that no data is lost.

See also setReadBufferSize() and read().

[override virtual protected] qint64 QAbstractSocket::readData(char *data, qint64 maxSize)

Reimplements: QIODevice::readData(char *data, qint64 maxSize).

[override virtual protected] qint64 QAbstractSocket::readLineData(char *data, qint64 maxlen)

Reimplements: QIODevice::readLineData(char *data, qint64 maxSize).

[virtual, since 5.0] void QAbstractSocket::resume()

Continues data transfer on the socket. This method should only be used after the socket has been set to pause upon notifications and a notification has been received. The only notification currently supported is QSslSocket::sslErrors(). Calling this method if the socket is not paused results in undefined behavior.

This function was introduced in Qt 5.0.

See also pauseMode() and setPauseMode().

[protected] void QAbstractSocket::setLocalAddress(const QHostAddress &address)

Sets the address on the local side of a connection to address.

You can call this function in a subclass of QAbstractSocket to change the return value of the localAddress() function after a connection has been established. This feature is commonly used by proxy connections for virtual connection settings.

Note that this function does not bind the local address of the socket prior to a connection (e.g., QAbstractSocket::bind()).

See also localAddress(), setLocalPort(), and setPeerAddress().

[protected] void QAbstractSocket::setLocalPort(quint16 port)

Sets the port on the local side of a connection to port.

You can call this function in a subclass of QAbstractSocket to change the return value of the localPort() function after a connection has been established. This feature is commonly used by proxy connections for virtual connection settings.

Note that this function does not bind the local port of the socket prior to a connection (e.g., QAbstractSocket::bind()).

See also localPort(), localAddress(), setLocalAddress(), and setPeerPort().

[since 5.0] void QAbstractSocket::setPauseMode(QAbstractSocket::PauseModes pauseMode)

Controls whether to pause upon receiving a notification. The pauseMode parameter specifies the conditions in which the socket should be paused. The only notification currently supported is QSslSocket::sslErrors(). If set to PauseOnSslErrors, data transfer on the socket will be paused and needs to be enabled explicitly again by calling resume(). By default this option is set to PauseNever. This option must be called before connecting to the server, otherwise it will result in undefined behavior.

This function was introduced in Qt 5.0.

See also pauseMode() and resume().

[protected] void QAbstractSocket::setPeerAddress(const QHostAddress &address)

Sets the address of the remote side of the connection to address.

You can call this function in a subclass of QAbstractSocket to change the return value of the peerAddress() function after a connection has been established. This feature is commonly used by proxy connections for virtual connection settings.

See also peerAddress(), setPeerPort(), and setLocalAddress().

[protected] void QAbstractSocket::setPeerName(const QString &name)

Sets the host name of the remote peer to name.

You can call this function in a subclass of QAbstractSocket to change the return value of the peerName() function after a connection has been established. This feature is commonly used by proxy connections for virtual connection settings.

See also peerName().

[protected] void QAbstractSocket::setPeerPort(quint16 port)

Sets the port of the remote side of the connection to port.

You can call this function in a subclass of QAbstractSocket to change the return value of the peerPort() function after a connection has been established. This feature is commonly used by proxy connections for virtual connection settings.

See also peerPort(), setPeerAddress(), and setLocalPort().

[since 5.13] void QAbstractSocket::setProtocolTag(const QString &tag)

Sets the protocol tag for this socket to tag.

This function was introduced in Qt 5.13.

See also protocolTag().

void QAbstractSocket::setProxy(const QNetworkProxy &networkProxy)

Sets the explicit network proxy for this socket to networkProxy.

To disable the use of a proxy for this socket, use the QNetworkProxy::NoProxy proxy type:

socket->setProxy(QNetworkProxy::NoProxy);

The default value for the proxy is QNetworkProxy::DefaultProxy, which means the socket will use the application settings: if a proxy is set with QNetworkProxy::setApplicationProxy, it will use that; otherwise, if a factory is set with QNetworkProxyFactory::setApplicationProxyFactory, it will query that factory with type QNetworkProxyQuery::TcpSocket.

See also proxy(), QNetworkProxy, and QNetworkProxyFactory::queryProxy().

[virtual] void QAbstractSocket::setReadBufferSize(qint64 size)

Sets the size of QAbstractSocket’s internal read buffer to be size bytes.

If the buffer size is limited to a certain size, QAbstractSocket won’t buffer more than this size of data. Exceptionally, a buffer size of 0 means that the read buffer is unlimited and all incoming data is buffered. This is the default.

This option is useful if you only read the data at certain points in time (e.g., in a real-time streaming application) or if you want to protect your socket against receiving too much data, which may eventually cause your application to run out of memory.

Only QTcpSocket uses QAbstractSocket’s internal buffer; QUdpSocket does not use any buffering at all, but rather relies on the implicit buffering provided by the operating system. Because of this, calling this function on QUdpSocket has no effect.

See also readBufferSize() and read().

[virtual] bool QAbstractSocket::setSocketDescriptor(qintptr socketDescriptor, QAbstractSocket::SocketState socketState = ConnectedState, QIODeviceBase::OpenMode openMode = ReadWrite)

Initializes QAbstractSocket with the native socket descriptor socketDescriptor. Returns true if socketDescriptor is accepted as a valid socket descriptor; otherwise returns false. The socket is opened in the mode specified by openMode, and enters the socket state specified by socketState. Read and write buffers are cleared, discarding any pending data.

Note: It is not possible to initialize two abstract sockets with the same native socket descriptor.

See also socketDescriptor().

[protected] void QAbstractSocket::setSocketError(QAbstractSocket::SocketError socketError)

Sets the type of error that last occurred to socketError.

See also setSocketState() and setErrorString().

[virtual] void QAbstractSocket::setSocketOption(QAbstractSocket::SocketOption option, const QVariant &value)

Sets the given option to the value described by value.

Note: On Windows Runtime, QAbstractSocket::KeepAliveOption must be set before the socket is connected.

See also socketOption().

[protected] void QAbstractSocket::setSocketState(QAbstractSocket::SocketState state)

Sets the state of the socket to state.

See also state().

[override virtual protected] qint64 QAbstractSocket::skipData(qint64 maxSize)

Reimplements: QIODevice::skipData(qint64 maxSize).

[virtual] qintptr QAbstractSocket::socketDescriptor() const

Returns the native socket descriptor of the QAbstractSocket object if this is available; otherwise returns -1.

If the socket is using QNetworkProxy, the returned descriptor may not be usable with native socket functions.

The socket descriptor is not available when QAbstractSocket is in UnconnectedState.

See also setSocketDescriptor().

[virtual] QVariant QAbstractSocket::socketOption(QAbstractSocket::SocketOption option)

Returns the value of the option option.

See also setSocketOption().

QAbstractSocket::SocketType QAbstractSocket::socketType() const

Returns the socket type (TCP, UDP, or other).

See also QTcpSocket and QUdpSocket.

QAbstractSocket::SocketState QAbstractSocket::state() const

Returns the state of the socket.

See also error().

[override virtual] bool QAbstractSocket::waitForBytesWritten(int msecs = 30000)

Reimplements: QIODevice::waitForBytesWritten(int msecs).

This function blocks until at least one byte has been written on the socket and the bytesWritten() signal has been emitted. The function will timeout after msecs milliseconds; the default timeout is 30000 milliseconds.

The function returns true if the bytesWritten() signal is emitted; otherwise it returns false (if an error occurred or the operation timed out).

Note: This function may fail randomly on Windows. Consider using the event loop and the bytesWritten() signal if your software will run on Windows.

See also waitForReadyRead().

[virtual] bool QAbstractSocket::waitForConnected(int msecs = 30000)

Waits until the socket is connected, up to msecs milliseconds. If the connection has been established, this function returns true; otherwise it returns false. In the case where it returns false, you can call error() to determine the cause of the error.

The following example waits up to one second for a connection to be established:

socket->connectToHost("imap", 143);
if (socket->waitForConnected(1000))
    qDebug("Connected!");

If msecs is -1, this function will not time out.

Note: This function may wait slightly longer than msecs, depending on the time it takes to complete the host lookup.

Note: Multiple calls to this functions do not accumulate the time. If the function times out, the connecting process will be aborted.

Note: This function may fail randomly on Windows. Consider using the event loop and the connected() signal if your software will run on Windows.

See also connectToHost() and connected().

[virtual] bool QAbstractSocket::waitForDisconnected(int msecs = 30000)

Waits until the socket has disconnected, up to msecs milliseconds. If the connection was successfully disconnected, this function returns true; otherwise it returns false (if the operation timed out, if an error occurred, or if this QAbstractSocket is already disconnected). In the case where it returns false, you can call error() to determine the cause of the error.

The following example waits up to one second for a connection to be closed:

socket->disconnectFromHost();
if (socket->state() == QAbstractSocket::UnconnectedState
    || socket->waitForDisconnected(1000)) {
        qDebug("Disconnected!");
}

If msecs is -1, this function will not time out.

Note: This function may fail randomly on Windows. Consider using the event loop and the disconnected() signal if your software will run on Windows.

See also disconnectFromHost() and close().

[override virtual] bool QAbstractSocket::waitForReadyRead(int msecs = 30000)

Reimplements: QIODevice::waitForReadyRead(int msecs).

This function blocks until new data is available for reading and the readyRead() signal has been emitted. The function will timeout after msecs milliseconds; the default timeout is 30000 milliseconds.

The function returns true if the readyRead() signal is emitted and there is new data available for reading; otherwise it returns false (if an error occurred or the operation timed out).

Note: This function may fail randomly on Windows. Consider using the event loop and the readyRead() signal if your software will run on Windows.

See also waitForBytesWritten().

[override virtual protected] qint64 QAbstractSocket::writeData(const char *data, qint64 size)

Reimplements: QIODevice::writeData(const char *data, qint64 maxSize).