QLocalSocket Class

See also QLocalServer

The LocalServerError enumeration represents the errors that can occur. The most recent error can be retrieved through a call to QLocalSocket::error().

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

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flags QLocalSocket::SocketOptions

This enum describes the possible options that can be used to connect to a server. Currently, on Linux and Android it is used for specifying connection to a server listening to a socket bound to an abstract address.

This enum was introduced or modified in Qt 6.2.

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

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This property supports QProperty bindings.

This property holds the socket options.

Options must be set while the socket is in UnconnectedState state.

This property was introduced in Qt 6.2.

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Creates a new local socket. The parent argument is passed to QObject's constructor.

Destroys the socket, closing the connection if necessary.

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

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Reimplements: QIODevice::bytesAvailable() const.

Reimplements: QIODevice::bytesToWrite() const.

Reimplements: QIODevice::canReadLine() const.

Reimplements: QIODevice::close().

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

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

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Attempts to make a connection to serverName(). setServerName() must be called before you open the connection. Alternatively you can use connectToServer(const QString &name, OpenMode openMode);

The socket is opened in the given openMode and first enters ConnectingState. If a connection is established, QLocalSocket enters ConnectedState and emits connected().

After calling this function, the socket can emit errorOccurred() to signal that an error occurred.

This function was introduced in Qt 5.1.

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This is an overloaded function.

Set the server name and attempts to make a connection to it.

The socket is opened in the given openMode and first enters ConnectingState. If a connection is established, QLocalSocket enters ConnectedState and emits connected().

After calling this function, the socket can emit errorOccurred() to signal that an error occurred.

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

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

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This signal is emitted when the socket has been disconnected.

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Returns the type of error that last occurred.

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

QLocalSocket::LocalSocketError 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.

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

Call this function if you need QLocalSocket 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 QLocalSocket will start sending data automatically once control goes back to the event loop. In the absence of an event loop, call waitForBytesWritten() instead.

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Returns the server path that the socket is connected to.

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Reimplements: QIODevice::isSequential() const.

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

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Reimplements: QIODevice::open(QIODeviceBase::OpenMode mode).

Equivalent to connectToServer(OpenMode mode). The socket is opened in the given openMode to the server defined by setServerName().

Note that unlike in most other QIODevice subclasses, open() may not open the device directly. The function return false if the socket was already connected or if the server to connect to was not defined and true in any other case. The connected() or errorOccurred() signals will be emitted once the device is actually open (or the connection failed).

See connectToServer() for more details.

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.

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

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

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

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Sets the size of QLocalSocket's internal read buffer to be size bytes.

If the buffer size is limited to a certain size, QLocalSocket 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.

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Set the name of the peer to connect to. On Windows name is the name of a named pipe; on Unix name is the name of a local domain socket.

This function must be called when the socket is not connected.

This function was introduced in Qt 5.1.

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Initializes QLocalSocket 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.

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Reimplements: QIODevice::skipData(qint64 maxSize).

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

The socket descriptor is not available when QLocalSocket is in UnconnectedState. The type of the descriptor depends on the platform:

• On Windows, the returned value is a Winsock 2 Socket Handle.

• On INTEGRITY, the returned value is the QTcpSocket socket descriptor and the type is defined by socketDescriptor.

• On all other UNIX-like operating systems, the type is a file descriptor representing a socket.

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Returns the state of the socket.

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This signal is emitted whenever QLocalSocket's state changes. The socketState parameter is the new state.

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

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Reimplements: QIODevice::waitForBytesWritten(int msecs).

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->connectToServer("market");
if (socket->waitForConnected(1000))
    qDebug("Connected!");

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

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

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

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Reimplements: QIODevice::waitForReadyRead(int msecs).

This function blocks until 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 data is available for reading; otherwise it returns false (if an error occurred or the operation timed out).

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