QAbstractSocket Class

     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;
     }

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).