QIODevice(3qt)QIODevice(3qt)NAME
QIODevice - The base class of I/O devices
#include <qiodevice.h>
Inherited by QBuffer, QFile, QSocket and QSocketDevice.
Public Members
QIODevice ()
virtual ~QIODevice ()
int flags () const
int mode () const
int state () const
bool isDirectAccess () const
bool isSequentialAccess () const
bool isCombinedAccess () const
bool isBuffered () const
bool isRaw () const
bool isSynchronous () const
bool isAsynchronous () const
bool isTranslated () const
bool isReadable () const
bool isWritable () const
bool isReadWrite () const
bool isInactive () const
bool isOpen () const
int status () const
void resetStatus ()
virtual bool open ( int mode )
virtual void close ()
virtual void flush ()
virtual uint size () const
virtual int at () const
virtual bool at ( int )
virtual bool atEnd () const
bool reset ()
virtual int readBlock ( char * data, uint maxlen )
virtual int writeBlock ( const char * data, uint len )
virtual int readLine ( char * data, uint maxlen )
int writeBlock ( const QByteArray & data )
QByteArray readAll ()
virtual int getch ()
virtual int putch ( int )
virtual int ungetch ( int )
Protected Members
void setFlags ( int f ) (internal)
void setType ( int ) (internal)
void setMode ( int ) (internal)
void setState ( int ) (internal)
void setStatus ( int ) (internal)
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QIODevice(3qt)QIODevice(3qt)DESCRIPTION
The QIODevice class is the base class of I/O devices.
An I/O device represents a medium that one can read bytes
from and/or write bytes to. The QIODevice class is the
abstract superclass of all such devices; classes like
QFile, QBuffer and QSocket inherit QIODevice and implement
virtual functions like write() appropriately.
While applications sometimes use QIODevice directly,
mostly it is better to go through QTextStream and
QDataStream, which provide stream operations on any
QIODevice subclass. QTextStream provides text-oriented
stream functionality (for human-readable ASCII files, for
example), while QDataStream deals with binary data in a
totally platform-independent manner.
The public member functions in QIODevice roughly fall into
two groups: The action functions and the state access
functions. The most important action functions are:
open() opens a device for reading and/or writing,
depending on the argument to open().
close() closes the device and tidies up.
readBlock() reads a block of data from the device.
writeBlock() writes a block of data to the device.
readLine() reads a line (of text, usually) from the
device.
flush() ensures that all buffered data are written to the
real device.
There are also some other, less used, action
functions:
getch() reads a single character.
ungetch() forgets the last call to getch(), if possible.
putch() writes a single character.
size() returns the size of the device, if there is one.
at() returns the current read/write pointer, if there is
one for this device, or it moves the pointer.
atEnd() says whether there is more to read, if that is a
meaningful question for this device.
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QIODevice(3qt)QIODevice(3qt)reset() moves the read/write pointer to the start of the
device, if that is possible for this device.
The state access are all "get" functions. The
QIODevice subclass calls setState() to update the
state, and simple access functions tell the user of
the device what the device's state is. Here are the
settings, and their associated access functions:
Access type. Some devices are direct access (it is
possible to read/write anywhere) while others are
sequential. QIODevice provides the access functions
isDirectAccess(), isSequentialAccess() and
isCombinedAccess() to tell users what a given I/O device
supports.
Buffering. Some devices are accessed in raw mode while
others are buffered. Buffering usually provides greater
efficiency, particularly for small read/write operations.
isBuffered() tells the user whether a given device is
buffered. (This can often be set by the application in the
call to open().)
Synchronicity. Synchronous devices work there and then,
for example files. When you read from a file, the file
delivers its data right away. Others, such as a socket
connected to a HTTP server, may not deliver the data until
seconds after you ask to read it. isSynchronous() and
isAsynchronous() tells the user how this device operates.
CR/LF translation. For simplicity, applications often like
to see just a single CR/LF style, and QIODevice subclasses
can provide that. isTranslated() returns TRUE if this
object translates CR/LF to just LF. (This can often be set
by the application in the call to open().)
Accessibility. Some files cannot be written, for example.
isReadable(), isWritable and isReadWrite() tells the
application whether it can read from and write to a given
device. (This can often be set by the application in the
call to open().)
Finally, isOpen() returns TRUE if the device is open. This
can quite obviously be set using open() :)
QIODevice provides numerous pure virtual functions you
need to implement when subclassing it. Here is a skeleton
subclass with all the members you are certain to need, and
some it's likely that you will need:
class YourDevice : public QIODevice
{
public:
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QIODevice(3qt)QIODevice(3qt)YourDevice();
~YourDevice();
bool open( int mode );
void close();
void flush();
uint size() const;
int at() const; // not a pure virtual function
bool at( int ); // not a pure virtual function
bool atEnd() const; // not a pure virtual function
int readBlock( char *data, uint maxlen );
int writeBlock( const char *data, uint len );
int readLine( char *data, uint maxlen );
int getch();
int putch( int );
int ungetch( int );
};
The three non-pure virtual functions can be ignored if
your device is sequential (e.g. an RS-232 port).
See also QDataStream and QTextStream.
MEMBER FUNCTION DOCUMENTATIONQIODevice::QIODevice ()
Constructs an I/O device.
QIODevice::~QIODevice () [virtual]
Destructs the I/O device.
bool QIODevice::at ( int pos ) [virtual]
Virtual function that sets the I/O device index to pos.
See also size().
Reimplemented in QBuffer, QSocketDevice, QSocket and
QFile.
int QIODevice::at () const [virtual]
Virtual function that returns the current I/O device
index.
This index is the data read/write head of the I/O device.
See also size().
Reimplemented in QBuffer, QFile, QSocket and
QSocketDevice.
bool QIODevice::atEnd () const [virtual]
Virtual function that returns TRUE if the I/O device index
is at the end of the input.
Reimplemented in QFile, QSocket and QSocketDevice.
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QIODevice(3qt)QIODevice(3qt)void QIODevice::close () [virtual]
Closes the I/O device.
This virtual function must be reimplemented by all
subclasses.
See also open().
Reimplemented in QBuffer, QSocketDevice, QFile and
QSocket.
int QIODevice::flags () const
Returns the current I/O device flags setting.
Flags consists of mode flags and state flags.
See also mode() and state().
void QIODevice::flush () [virtual]
Flushes an open I/O device.
This virtual function must be reimplemented by all
subclasses.
Reimplemented in QFile, QSocket, QBuffer and
QSocketDevice.
int QIODevice::getch () [virtual]
Reads a single byte/character from the I/O device.
Returns the byte/character read, or -1 if the end of the
I/O device has been reached.
This virtual function must be reimplemented by all
subclasses.
See also putch() and ungetch().
Reimplemented in QSocketDevice, QFile, QBuffer and
QSocket.
bool QIODevice::isAsynchronous () const
Returns TRUE if the I/O device is a asynchronous device,
otherwise FALSE.
This mode is currently not in use.
See also isSynchronous().
bool QIODevice::isBuffered () const
Returns TRUE if the I/O device is a buffered (not raw)
device, otherwise FALSE.
See also isRaw().
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QIODevice(3qt)QIODevice(3qt)bool QIODevice::isCombinedAccess () const
Returns TRUE if the I/O device is a combined access (both
direct and sequential) device, otherwise FALSE.
This access method is currently not in use.
bool QIODevice::isDirectAccess () const
Returns TRUE if the I/O device is a direct access (not
sequential) device, otherwise FALSE.
See also isSequentialAccess().
bool QIODevice::isInactive () const
Returns TRUE if the I/O device state is 0, i.e. the device
is not open.
See also isOpen().
bool QIODevice::isOpen () const
Returns TRUE if the I/O device state has been opened,
otherwise FALSE.
See also isInactive().
bool QIODevice::isRaw () const
Returns TRUE if the I/O device is a raw (not buffered)
device, otherwise FALSE.
See also isBuffered().
bool QIODevice::isReadWrite () const
Returns TRUE if the I/O device was opened using
IO_ReadWrite mode.
See also isReadable() and isWritable().
bool QIODevice::isReadable () const
Returns TRUE if the I/O device was opened using
IO_ReadOnly or IO_ReadWrite mode.
See also isWritable() and isReadWrite().
bool QIODevice::isSequentialAccess () const
Returns TRUE if the I/O device is a sequential access (not
direct) device, otherwise FALSE. Operations involving
size() and at(int) are not valid on sequential devices.
See also isDirectAccess().
bool QIODevice::isSynchronous () const
Returns TRUE if the I/O device is a synchronous device,
otherwise FALSE.
See also isAsynchronous().
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QIODevice(3qt)QIODevice(3qt)bool QIODevice::isTranslated () const
Returns TRUE if the I/O device translates carriage-return
and linefeed characters.
A QFile is translated if it is opened with the
IO_Translate mode flag.
bool QIODevice::isWritable () const
Returns TRUE if the I/O device was opened using
IO_WriteOnly or IO_ReadWrite mode.
See also isReadable() and isReadWrite().
int QIODevice::mode () const
Returns bits OR'ed together that specify the current
operation mode.
These are the flags that were given to the open()
function.
The flags are: IO_ReadOnly, IO_WriteOnly, IO_ReadWrite,
IO_Append, IO_Truncate and IO_Translate.
bool QIODevice::open ( int mode ) [virtual]
Opens the I/O device using the specified mode. Returns
TRUE if successful, or FALSE if the device could not be
opened.
The mode parameter m must be a combination of the
following flags.
IO_Raw specified raw (unbuffered) file access.
IO_ReadOnly opens a file in read-only mode.
IO_WriteOnly opens a file in write-only mode.
IO_ReadWrite opens a file in read/write mode.
IO_Append sets the file index to the end of the file.
IO_Truncate truncates the file.
IO_Translate enables carriage returns and linefeed
translation for text files under MS-DOS, Window, OS/2 and
Macintosh. On Unix systems this flag has no effect. Use
with caution as it will also transform every linefeed
written to the file into a CRLF pair. This is likely to
corrupt your file when writing binary data to it. Cannot
be combined with IO_Raw.
This virtual function must be reimplemented by all
subclasses.
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QIODevice(3qt)QIODevice(3qt)
See also close().
Reimplemented in QBuffer, QFile, QSocketDevice and
QSocket.
int QIODevice::putch ( int ch ) [virtual]
Writes the character ch to the I/O device.
Returns ch, or -1 if some error occurred.
This virtual function must be reimplemented by all
subclasses.
See also getch() and ungetch().
Reimplemented in QSocket, QBuffer, QSocketDevice and
QFile.
QByteArray QIODevice::readAll ()
This convenience function returns all of the remaining
data in the device. Note that this only works for direct
access devices, such as QFile.
See also isDirectAccess().
int QIODevice::readBlock ( char * data, uint maxlen ) [virtual]
Reads at most maxlen bytes from the I/O device into data
and returns the number of bytes actually read.
This virtual function must be reimplemented by all
subclasses.
See also writeBlock().
Reimplemented in QBuffer, QSocket, QSocketDevice and
QFile.
int QIODevice::readLine ( char * data, uint maxlen ) [virtual]
Reads a line of text, up to maxlen bytes including a
terminating \0. If there is a newline at the end if the
line, it is not stripped.
Returns the number of bytes read, or -1 in case of error.
This virtual function can be reimplemented much more
efficiently by the most subclasses.
See also readBlock() and QTextStream::readLine().
Reimplemented in QSocket, QBuffer and QFile.
bool QIODevice::reset ()
Sets the device index to 0.
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QIODevice(3qt)QIODevice(3qt)
See also at().
void QIODevice::resetStatus ()
Sets the I/O device status to IO_Ok.
See also status().
uint QIODevice::size () const [virtual]
Virtual function that returns the size of the I/O device.
See also at().
Reimplemented in QSocket, QFile, QBuffer and
QSocketDevice.
int QIODevice::state () const
Returns bits OR'ed together that specify the current
state.
The flags are: IO_Open.
Subclasses may define more flags.
int QIODevice::status () const
Returns the I/O device status.
The I/O device status returns an error code. If open()
returns FALSE or readBlock() or writeBlock() return -1,
this function can be called to get the reason why the
operation did not succeed.
The status codes are:
IO_Ok The operation was successful.
IO_ReadError Could not read from the device.
IO_WriteError Could not write to the device.
IO_FatalError A fatal unrecoverable error occurred.
IO_OpenError Could not open the device.
IO_ConnectError Could not connect to the device.
IO_AbortError The operation was unexpectedly aborted.
IO_TimeOutError The operation timed out.
IO_OnCloseError An unspecified error happened on close.
See also resetStatus().
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QIODevice(3qt)QIODevice(3qt)int QIODevice::ungetch ( int ch ) [virtual]
Puts the character ch back into the I/O device and
decrements the index if it is not zero.
This function is normally called to "undo" a getch()
operation.
Returns ch, or -1 if some error occurred.
This virtual function must be reimplemented by all
subclasses.
See also getch() and putch().
Reimplemented in QBuffer, QFile, QSocketDevice and
QSocket.
int QIODevice::writeBlock ( const QByteArray & data )
This convenience function is the same as calling
writeBlock( data.data(), data.size() ).
int QIODevice::writeBlock ( const char * data, uint len )
[virtual]
Writes len bytes from p to the I/O device and returns the
number of bytes actually written.
This virtual function must be reimplemented by all
subclasses.
See also readBlock().
Reimplemented in QBuffer, QSocketDevice, QFile and
QSocket.
void QIODevice::setFlags ( int f ) [protected]
For internal use only.
void QIODevice::setMode ( int m ) [protected]
For internal use only.
void QIODevice::setState ( int s ) [protected]
For internal use only.
void QIODevice::setStatus ( int s ) [protected]
For internal use only.
void QIODevice::setType ( int t ) [protected]
For internal use only.
SEE ALSO
http://doc.trolltech.com/qiodevice.html
http://www.trolltech.com/faq/tech.html
Trolltech AS 13 June 2001 10
QIODevice(3qt)QIODevice(3qt)COPYRIGHT
Copyright 1992-2001 Trolltech AS,
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
If you find a bug in Qt, please report it as described in
http://doc.trolltech.com/bughowto.html. Good bug reports
make our job much simpler. Thank you.
In case of content or formattting problems with this
manual page, please report them to qt-bugs@trolltech.com.
Please include the name of the manual page (qiodevice.3qt)
and the Qt version (2.3.1).
Trolltech AS 13 June 2001 11
