QSocket(3qt)QSocket(3qt)NAMEQSocket - Buffered TCP connection
SYNOPSIS
#include <qsocket.h>
Inherits QObject and QIODevice.
Public Members
enum Error { ErrConnectionRefused, ErrHostNotFound, ErrSocketRead }
QSocket ( QObject * parent = 0, const char * name = 0 )
virtual ~QSocket ()
enum State { Idle, HostLookup, Connecting, Connected, Closing,
Connection = Connected }
State state () const
int socket () const
virtual void setSocket ( int socket )
QSocketDevice * socketDevice ()
virtual void setSocketDevice ( QSocketDevice * device )
virtual void connectToHost ( const QString & host, Q_UINT16 port )
QString peerName () const
virtual bool open ( int m )
virtual void close ()
virtual void flush ()
virtual Offset size () const
virtual Offset at () const
virtual bool at ( Offset index )
virtual bool atEnd () const
Q_ULONG bytesAvailable () const
Q_ULONG waitForMore ( int msecs, bool * timeout ) const
Q_ULONG waitForMore ( int msecs ) const
Q_ULONG bytesToWrite () const
void clearPendingData ()
virtual Q_LONG readBlock ( char * data, Q_ULONG maxlen )
virtual Q_LONG writeBlock ( const char * data, Q_ULONG len )
virtual int getch ()
virtual int putch ( int ch )
virtual int ungetch ( int ch )
bool canReadLine () const
virtual QString readLine ()
Q_UINT16 port () const
Q_UINT16 peerPort () const
QHostAddress address () const
QHostAddress peerAddress () const
void setReadBufferSize ( Q_ULONG bufSize )
Q_ULONG readBufferSize () const
Signals
void hostFound ()
void connected ()
void connectionClosed ()
void delayedCloseFinished ()
void readyRead ()
void bytesWritten ( int nbytes )
void error ( int )
DESCRIPTION
The QSocket class provides a buffered TCP connection.
It provides a totally non-blocking QIODevice, and modifies and extends
the API of QIODevice with socket-specific code.
Note that a QApplication must have been constructed before this class
can be used.
The functions you're likely to call most are connectToHost(),
bytesAvailable(), canReadLine() and the ones it inherits from
QIODevice.
connectToHost() is the most-used function. As its name implies, it
opens a connection to a named host.
Most network protocols are either packet-oriented or line-oriented.
canReadLine() indicates whether a connection contains an entire unread
line or not, and bytesAvailable() returns the number of bytes available
for reading.
The signals error(), connected(), readyRead() and connectionClosed()
inform you of the progress of the connection. There are also some less
commonly used signals. hostFound() is emitted when connectToHost() has
finished its DNS lookup and is starting its TCP connection.
delayedCloseFinished() is emitted when close() succeeds. bytesWritten()
is emitted when QSocket moves data from its "to be written" queue into
the TCP implementation.
There are several access functions for the socket: state() returns
whether the object is idle, is doing a DNS lookup, is connecting, has
an operational connection, etc. address() and port() return the IP
address and port used for the connection. The peerAddress() and
peerPort() functions return the IP address and port used by the peer,
and peerName() returns the name of the peer (normally the name that was
passed to connectToHost()). socketDevice() returns a pointer to the
QSocketDevice used for this socket.
QSocket inherits QIODevice, and reimplements some functions. In
general, you can treat it as a QIODevice for writing, and mostly also
for reading. The match isn't perfect, since the QIODevice API is
designed for devices that are controlled by the same machine, and an
asynchronous peer-to-peer network connection isn't quite like that. For
example, there is nothing that matches QIODevice::size() exactly. The
documentation for open(), close(), flush(), size(), at(), atEnd(),
readBlock(), writeBlock(), getch(), putch(), ungetch() and readLine()
describes the differences in detail.
Warning: QSocket is not suitable for use in threads. If you need to
uses sockets in threads use the lower-level QSocketDevice class.
Warning: Because Qt doesn't use the native socketstream implementation
on Mac OS X, QSocket has an implicit transfer latency of 100ms. You can
achieve lower latency on Mac OS X by using QSocketDevice instead.
See also QSocketDevice, QHostAddress, QSocketNotifier, and Input/Output
and Networking.
Member Type Documentation
QSocket::Error
This enum specifies the possible errors:
QSocket::ErrConnectionRefused - if the connection was refused
QSocket::ErrHostNotFound - if the host was not found
QSocket::ErrSocketRead - if a read from the socket failed
QSocket::State
This enum defines the connection states:
QSocket::Idle - if there is no connection
QSocket::HostLookup - during a DNS lookup
QSocket::Connecting - during TCP connection establishment
QSocket::Connected - when there is an operational connection
QSocket::Closing - if the socket is closing down, but is not yet
closed.
MEMBER FUNCTION DOCUMENTATIONQSocket::QSocket ( QObject * parent = 0, const char * name = 0 )
Creates a QSocket object in QSocket::Idle state.
The parent and name arguments are passed on to the QObject constructor.
Note that a QApplication must have been constructed before sockets can
be used.
QSocket::~QSocket () [virtual]
Destroys the socket. Closes the connection if necessary.
See also close().
QHostAddress QSocket::address () const
Returns the host address of this socket. (This is normally the main IP
address of the host, but can be e.g. 127.0.0.1 for connections to
localhost.)
Offset QSocket::at () const [virtual]
Returns the current read index. Since QSocket is a sequential device,
the current read index is always zero.
Reimplemented from QIODevice.
bool QSocket::at ( Offset index ) [virtual]
This is an overloaded member function, provided for convenience. It
behaves essentially like the above function.
Moves the read index forward to index and returns TRUE if the operation
was successful; otherwise returns FALSE. Moving the index forward means
skipping incoming data.
Reimplemented from QIODevice.
bool QSocket::atEnd () const [virtual]
Returns TRUE if there is no more data to read; otherwise returns FALSE.
Reimplemented from QIODevice.
Q_ULONG QSocket::bytesAvailable () const
Returns the number of incoming bytes that can be read, i.e. the size of
the input buffer. Equivalent to size().
This function can trigger the readyRead() signal, if more data has
arrived on the socket.
See also bytesToWrite().
Example: network/networkprotocol/nntp.cpp.
Q_ULONG QSocket::bytesToWrite () const
Returns the number of bytes that are waiting to be written, i.e. the
size of the output buffer.
See also bytesAvailable() and clearPendingData().
void QSocket::bytesWritten ( int nbytes ) [signal]
This signal is emitted when data has been written to the network. The
nbytes parameter specifies how many bytes were written.
The bytesToWrite() function is often used in the same context; it
indicates how many buffered bytes there are left to write.
See also writeBlock() and bytesToWrite().
bool QSocket::canReadLine () const
Returns TRUE if it's possible to read an entire line of text from this
socket at this time; otherwise returns FALSE.
Note that if the peer closes the connection unexpectedly, this function
returns FALSE. This means that loops such as this won't work:
while( !socket->canReadLine() ) // WRONG
;
See also readLine().
Examples:
void QSocket::clearPendingData ()
Deletes the data that is waiting to be written. This is useful if you
want to close the socket without waiting for all the data to be
written.
See also bytesToWrite(), close(), and delayedCloseFinished().
void QSocket::close () [virtual]
Closes the socket.
The read buffer is cleared.
If the output buffer is empty, the state is set to QSocket::Idle and
the connection is terminated immediately. If the output buffer still
contains data to be written, QSocket goes into the QSocket::Closing
state and the rest of the data will be written. When all of the
outgoing data have been written, the state is set to QSocket::Idle and
the connection is terminated. At this point, the delayedCloseFinished()
signal is emitted.
If you don't want that the data of the output buffer is written, call
clearPendingData() before you call close().
See also state(), bytesToWrite(), and clearPendingData().
Examples:
Reimplemented from QIODevice.
void QSocket::connectToHost ( const QString & host, Q_UINT16 port ) [virtual]
Attempts to make a connection to host on the specified port and return
immediately.
Any connection or pending connection is closed immediately, and QSocket
goes into the HostLookup state. When the lookup succeeds, it emits
hostFound(), starts a TCP connection and goes into the Connecting
state. Finally, when the connection succeeds, it emits connected() and
goes into the Connected state. If there is an error at any point, it
emits error().
host may be an IP address in string form, or it may be a DNS name.
QSocket will do a normal DNS lookup if required. Note that port is in
native byte order, unlike some other libraries.
See also state().
Examples:
void QSocket::connected () [signal]
This signal is emitted after connectToHost() has been called and a
connection has been successfully established.
See also connectToHost() and connectionClosed().
Examples:
void QSocket::connectionClosed () [signal]
This signal is emitted when the other end has closed the connection.
The read buffers may contain buffered input data which you can read
after the connection was closed.
See also connectToHost() and close().
Examples:
void QSocket::delayedCloseFinished () [signal]
This signal is emitted when a delayed close is finished.
If you call close() and there is buffered output data to be written,
QSocket goes into the QSocket::Closing state and returns immediately.
It will then keep writing to the socket until all the data has been
written. Then, the delayedCloseFinished() signal is emitted.
See also close().
Examples:
void QSocket::error ( int ) [signal]
This signal is emitted after an error occurred. The parameter is the
Error value.
Examples:
void QSocket::flush () [virtual]
Implementation of the abstract virtual QIODevice::flush() function.
Reimplemented from QIODevice.
int QSocket::getch () [virtual]
Reads a single byte/character from the internal read buffer. Returns
the byte/character read, or -1 if there is nothing to be read.
See also bytesAvailable() and putch().
Reimplemented from QIODevice.
void QSocket::hostFound () [signal]
This signal is emitted after connectToHost() has been called and the
host lookup has succeeded.
See also connected().
Example: network/networkprotocol/nntp.cpp.
bool QSocket::open ( int m ) [virtual]
Opens the socket using the specified QIODevice file mode m. This
function is called automatically when needed and you should not call it
yourself.
See also close().
Reimplemented from QIODevice.
QHostAddress QSocket::peerAddress () const
Returns the address of the connected peer if the socket is in Connected
state; otherwise an empty QHostAddress is returned.
QString QSocket::peerName () const
Returns the host name as specified to the connectToHost() function. An
empty string is returned if none has been set.
Example: network/mail/smtp.cpp.
Q_UINT16 QSocket::peerPort () const
Returns the peer's host port number, normally as specified to the
connectToHost() function. If none has been set, this function returns
0.
Note that Qt always uses native byte order, i.e. 67 is 67 in Qt; there
is no need to call htons().
Q_UINT16 QSocket::port () const
Returns the host port number of this socket, in native byte order.
int QSocket::putch ( int ch ) [virtual]
Writes the character ch to the output buffer.
Returns ch, or -1 if an error occurred.
See also getch().
Reimplemented from QIODevice.
Q_LONG QSocket::readBlock ( char * data, Q_ULONG maxlen ) [virtual]
Reads maxlen bytes from the socket into data and returns the number of
bytes read. Returns -1 if an error occurred.
Example: network/networkprotocol/nntp.cpp.
Reimplemented from QIODevice.
Q_ULONG QSocket::readBufferSize () const
Returns the size of the read buffer.
See also setReadBufferSize().
QString QSocket::readLine () [virtual]
Returns a line of text including a terminating newline character (\n).
Returns "" if canReadLine() returns FALSE.
See also canReadLine().
Examples:
void QSocket::readyRead () [signal]
This signal is emitted every time there is new incoming data.
Bear in mind that new incoming data is only reported once; if you do
not read all the data, this class buffers the data and you can read it
later, but no signal is emitted unless new data arrives. A good
practice is to read all data in the slot connected to this signal
unless you are sure that you need to receive more data to be able to
process it.
See also readBlock(), readLine(), and bytesAvailable().
Examples:
void QSocket::setReadBufferSize ( Q_ULONG bufSize )
Sets the size of the QSocket's internal read buffer to bufSize.
Usually QSocket reads all data that is available from the operating
system's socket. If the buffer size is limited to a certain size, this
means that the QSocket class doesn't buffer more than this size of
data.
If the size of the read buffer is 0, the read buffer is unlimited and
all incoming data is buffered. This is the default.
If you read the data in the readyRead() signal, you shouldn't use this
option since it might slow down your program unnecessary. This option
is useful if you only need to read the data at certain points in time,
like in a realtime streaming application.
See also readBufferSize().
void QSocket::setSocket ( int socket ) [virtual]
Sets the socket to use socket and the state() to Connected. The socket
must already be connected.
This allows us to use the QSocket class as a wrapper for other socket
types (e.g. Unix Domain Sockets).
Example: network/httpd/httpd.cpp.
void QSocket::setSocketDevice ( QSocketDevice * device ) [virtual]
Sets the internal socket device to device. Passing a device of 0 will
cause the internal socket device to be used. Any existing connection
will be disconnected before using the new device.
The new device should not be connected before being associated with a
QSocket; after setting the socket call connectToHost() to make the
connection.
This function is useful if you need to subclass QSocketDevice and want
to use the QSocket API, for example, to implement Unix domain sockets.
Offset QSocket::size () const [virtual]
Returns the number of incoming bytes that can be read right now (like
bytesAvailable()).
Reimplemented from QIODevice.
int QSocket::socket () const
Returns the socket number, or -1 if there is no socket at the moment.
QSocketDevice * QSocket::socketDevice ()
Returns a pointer to the internal socket device.
There is normally no need to manipulate the socket device directly
since this class does the necessary setup for most applications.
State QSocket::state () const
Returns the current state of the socket connection.
See also QSocket::State.
Examples:
int QSocket::ungetch ( int ch ) [virtual]
This implementation of the virtual function QIODevice::ungetch()
prepends the character ch to the read buffer so that the next read
returns this character as the first character of the output.
Reimplemented from QIODevice.
Q_ULONG QSocket::waitForMore ( int msecs, bool * timeout ) const
Wait up to msecs milliseconds for more data to be available.
If msecs is -1 the call will block indefinitely.
Returns the number of bytes available.
If timeout is non-null and no error occurred (i.e. it does not return
-1): this function sets *timeout to TRUE, if the reason for returning
was that the timeout was reached; otherwise it sets *timeout to FALSE.
This is useful to find out if the peer closed the connection.
Warning: This is a blocking call and should be avoided in event driven
applications.
See also bytesAvailable().
Q_ULONG QSocket::waitForMore ( int msecs ) const
This is an overloaded member function, provided for convenience. It
behaves essentially like the above function.
Q_LONG QSocket::writeBlock ( const char * data, Q_ULONG len ) [virtual]
Writes len bytes to the socket from data and returns the number of
bytes written. Returns -1 if an error occurred.
Example: network/networkprotocol/nntp.cpp.
Reimplemented from QIODevice.
SEE ALSO
http://doc.trolltech.com/qsocket.html
http://www.trolltech.com/faq/tech.html
COPYRIGHT
Copyright 1992-2007 Trolltech ASA, http://www.trolltech.com. See the
license file included in the distribution for a complete license
statement.
AUTHOR
Generated automatically from the source code.
BUGS
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http://doc.trolltech.com/bughowto.html. Good bug reports help us to
help you. Thank you.
The definitive Qt documentation is provided in HTML format; it is
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If you find errors in this manual page, please report them to qt-
bugs@trolltech.com. Please include the name of the manual page
(qsocket.3qt) and the Qt version (3.3.8).
Trolltech AS 2 February 2007 QSocket(3qt)
