QLocalServer Class

Member Function Documentation

QLocalServer::QLocalServer(QObject *parent = nullptr)

Create a new local socket server with the given parent.

See also listen().

[signal] void QLocalServer::newConnection()

This signal is emitted every time a new connection is available.

See also hasPendingConnections() and nextPendingConnection().

[virtual] QLocalServer::~QLocalServer()

Destroys the QLocalServer object. If the server is listening for connections, it is automatically closed.

Any client QLocalSockets that are still connected must either disconnect or be reparented before the server is deleted.

See also close().

void QLocalServer::close()

Stop listening for incoming connections. Existing connections are not affected, but any new connections will be refused.

See also isListening() and listen().

QString QLocalServer::errorString() const

Returns the human-readable message appropriate to the current error reported by serverError(). If no suitable string is available, an empty string is returned.

See also serverError().

QString QLocalServer::fullServerName() const

Returns the full path that the server is listening on.

Note: This is platform specific

See also listen() and serverName().

[virtual] bool QLocalServer::hasPendingConnections() const

Returns true if the server has a pending connection; otherwise returns false.

See also nextPendingConnection() and setMaxPendingConnections().

[virtual protected] void QLocalServer::incomingConnection(quintptr socketDescriptor)

This virtual function is called by QLocalServer when a new connection is available. socketDescriptor is the native socket descriptor for the accepted connection.

The base implementation creates a QLocalSocket, sets the socket descriptor and then stores the QLocalSocket in an internal list of pending connections. Finally newConnection() is emitted.

Reimplement this function to alter the server's behavior when a connection is available.

See also newConnection(), nextPendingConnection(), and QLocalSocket::setSocketDescriptor().

bool QLocalServer::isListening() const

Returns true if the server is listening for incoming connections otherwise false.

See also listen() and close().

bool QLocalServer::listen(const QString &name)

Tells the server to listen for incoming connections on name. If the server is currently listening then it will return false. Return true on success otherwise false.

name can be a single name and QLocalServer will determine the correct platform specific path. serverName() will return the name that is passed into listen.

Usually you would just pass in a name like "foo", but on Unix this could also be a path such as "/tmp/foo" and on Windows this could be a pipe path such as "\\.\pipe\foo"

See also serverName(), isListening(), and close().

[since 5.0] bool QLocalServer::listen(qintptr socketDescriptor)

Instructs the server to listen for incoming connections on socketDescriptor. The property returns false if the server is currently listening. It returns true on success; otherwise, it returns false. The socket must be ready to accept new connections with no extra platform-specific functions called. The socket is set into non-blocking mode.

serverName(), fullServerName() may return a string with a name if this option is supported by the platform; otherwise, they return an empty QString. In particular, the addresses of sockets in the abstract namespace supported by Linux will not yield useful names if they contain unprintable characters.

This function was introduced in Qt 5.0.

See also isListening() and close().

[since 6.3] int QLocalServer::listenBacklogSize() const

Returns the backlog queue size of to be accepted connections.

This function was introduced in Qt 6.3.

See also setListenBacklogSize().

int QLocalServer::maxPendingConnections() const

Returns the maximum number of pending accepted connections. The default is 30.

See also setMaxPendingConnections() and hasPendingConnections().

[virtual] QLocalSocket *QLocalServer::nextPendingConnection()

Returns the next pending connection as a connected QLocalSocket object.

The socket is created as a child of the server, which means that it is automatically deleted when the QLocalServer object is destroyed. It is still a good idea to delete the object explicitly when you are done with it, to avoid wasting memory.

nullptr is returned if this function is called when there are no pending connections.

See also hasPendingConnections(), newConnection(), and incomingConnection().

[static] bool QLocalServer::removeServer(const QString &name)

Removes any server instance that might cause a call to listen() to fail and returns true if successful; otherwise returns false. This function is meant to recover from a crash, when the previous server instance has not been cleaned up.

On Windows, this function does nothing; on Unix, it removes the socket file given by name.

QAbstractSocket::SocketError QLocalServer::serverError() const

Returns the type of error that occurred last or NoError.

See also errorString().

QString QLocalServer::serverName() const

Returns the server name if the server is listening for connections; otherwise returns QString()

See also listen() and fullServerName().

[since 6.3] void QLocalServer::setListenBacklogSize(int size)

Sets the backlog queue size of to be accepted connections to size. The operating system might reduce or ignore this value. By default, the queue size is 50.

This function was introduced in Qt 6.3.

See also listenBacklogSize().

void QLocalServer::setMaxPendingConnections(int numConnections)

Sets the maximum number of pending accepted connections to numConnections. QLocalServer will accept no more than numConnections incoming connections before nextPendingConnection() is called.

Note: Even though QLocalServer will stop accepting new connections after it has reached its maximum number of pending connections, the operating system may still keep them in queue which will result in clients signaling that it is connected.

See also maxPendingConnections() and hasPendingConnections().

[since 5.10] qintptr QLocalServer::socketDescriptor() const

Returns the native socket descriptor the server uses to listen for incoming instructions, or -1 if the server is not listening.

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 QTcpServer socket descriptor and the type is defined by socketDescriptor.
• On all other UNIX-like operating systems, the type is a file descriptor representing a listening socket.

This function was introduced in Qt 5.10.

See also listen().

[since 5.0] QLocalServer::SocketOptions QLocalServer::socketOptions() const

Returns the socket options set on the socket.

Note: Getter function for property socketOptions.

This function was introduced in Qt 5.0.

See also setSocketOptions().

bool QLocalServer::waitForNewConnection(int msec = 0, bool *timedOut = nullptr)

Waits for at most msec milliseconds or until an incoming connection is available. Returns true if a connection is available; otherwise returns false. If the operation timed out and timedOut is not nullptr, *timedOut will be set to true.

This is a blocking function call. Its use is ill-advised in a single-threaded GUI application, since the whole application will stop responding until the function returns. waitForNewConnection() is mostly useful when there is no event loop available.

The non-blocking alternative is to connect to the newConnection() signal.

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

See also hasPendingConnections() and nextPendingConnection().