QIODevice Class Reference
The QIODevice class is the base class of I/O devices.
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#include <qiodevice.h>
Inherited by QBuffer, QFile, QSocket and QSocketDevice.
List of all member functions.
Public Members
virtual bool
open ( int mode ) = 0
virtual void
close () = 0
virtual void
flush () = 0
virtual Offset
size () const = 0
virtual Offset
at () const
virtual bool
at ( Offset pos )
virtual bool
atEnd () const
virtual Q_LONG
readBlock ( char * data, Q_ULONG maxlen ) = 0
virtual Q_LONG
writeBlock ( const char * data, Q_ULONG len ) = 0
virtual Q_LONG
readLine ( char * data, Q_ULONG maxlen )
virtual int
putch ( int ch ) = 0
Detailed 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 such as QFile, QBuffer and
QSocket inherit QIODevice and implement virtual functions such as
write() appropriately.
Although applications sometimes use QIODevice directly, it is
usually 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), whereas 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's position, 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.
- 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), whereas 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, whereas 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 immediately (for
example, files). When you read from a file, the file delivers its
data straight away. Other kinds of device, 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() tell
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
this. 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().)
- Permissions. Some files cannot be written. For example,
isReadable(), isWritable() and isReadWrite() tell 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, i.e. after
an open() call.
QIODevice provides numerous pure virtual functions that you need to
implement when subclassing it. Here is a skeleton subclass with all
the members you are certain to need and some that you probably
will need:
class MyDevice : public QIODevice
{
public:
MyDevice();
~MyDevice();
bool open( int mode );
void close();
void flush();
uint size() const;
int at() const; // non-pure virtual
bool at( int ); // non-pure virtual
bool atEnd() const; // non-pure virtual
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 need not be reimplemented
for sequential devices.
See also QDataStream, QTextStream and Input/Output and Networking.
Member Type Documentation
QIODevice::Offset
The offset within the device.
Member Function Documentation
QIODevice::QIODevice ()
Constructs an I/O device.
QIODevice::~QIODevice () [virtual]
Destroys the I/O device.
Offset QIODevice::at () const [virtual]
Virtual function that returns the current I/O device position.
This is the position of the data read/write head of the I/O device.
See also size().
Reimplemented in QFile and QSocket.
bool QIODevice::at ( Offset pos ) [virtual]
This is an overloaded member function, provided for convenience. It behaves essentially like the above function.
Virtual function that sets the I/O device position to pos.
See also size().
Reimplemented in QFile and QSocket.
bool QIODevice::atEnd () const [virtual]
Virtual function that returns TRUE if the I/O device position is at the
end of the input; otherwise returns FALSE.
Reimplemented in QFile and QSocket.
void QIODevice::close () [pure virtual]
Closes the I/O device.
This virtual function must be reimplemented by all subclasses.
See also open().
Example: grapher/grapher.cpp.
Reimplemented in 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 () [pure virtual]
Flushes an open I/O device.
This virtual function must be reimplemented by all subclasses.
Reimplemented in QFile and QSocket.
int QIODevice::getch () [pure 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 QFile and QSocket.
bool QIODevice::isAsynchronous () const
Returns TRUE if the device is an asynchronous device; otherwise
returns FALSE, i.e. if the device is a synchronous device.
This mode is currently not in use.
See also isSynchronous().
bool QIODevice::isBuffered () const
Returns TRUE if the I/O device is a buffered device; otherwise
returns FALSE, i.e. the device is a raw device.
See also isRaw().
bool QIODevice::isCombinedAccess () const
Returns TRUE if the I/O device is a combined access (both direct and
sequential) device; otherwise returns FALSE.
This access method is currently not in use.
bool QIODevice::isDirectAccess () const
Returns TRUE if the I/O device is a direct access device; otherwise
returns FALSE, i.e. if the device is a sequential access device.
See also isSequentialAccess().
bool QIODevice::isInactive () const
Returns TRUE if the I/O device state is 0, i.e. the device is not
open; otherwise returns FALSE.
See also isOpen().
bool QIODevice::isOpen () const
Returns TRUE if the I/O device has been opened; otherwise returns FALSE.
See also isInactive().
Example: network/networkprotocol/nntp.cpp.
bool QIODevice::isRaw () const
Returns TRUE if the device is a raw device; otherwise
returns FALSE, i.e. if the device is a buffered device.
See also isBuffered().
bool QIODevice::isReadWrite () const
Returns TRUE if the I/O device was opened using IO_ReadWrite
mode; otherwise returns FALSE.
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; otherwise returns FALSE.
See also isWritable() and isReadWrite().
bool QIODevice::isSequentialAccess () const
Returns TRUE if the device is a sequential access device; otherwise
returns FALSE, i.e. if the device is a direct access device.
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
returns FALSE, i.e. the device is an asynchronous device.
See also isAsynchronous().
bool QIODevice::isTranslated () const
Returns TRUE if the I/O device translates carriage-return and linefeed
characters; otherwise returns FALSE.
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; otherwise returns FALSE.
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 ) [pure virtual]
Opens the I/O device using the specified mode.
Returns TRUE if the device was successfully opened; otherwise
returns FALSE.
The mode parameter mode must be an OR'ed 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, Windows 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 if you write write binary data. Cannot be combined
with IO_Raw.
This virtual function must be reimplemented by all subclasses.
See also close().
Example: grapher/grapher.cpp.
Reimplemented in QFile and QSocket.
int QIODevice::putch ( int ch ) [pure virtual]
Writes the character ch to the I/O device.
Returns ch, or -1 if an error occurred.
This virtual function must be reimplemented by all subclasses.
See also getch() and ungetch().
Example: grapher/grapher.cpp.
Reimplemented in QFile and QSocket.
QByteArray QIODevice::readAll () [virtual]
This convenience function returns all of the remaining data in the
device.
Q_LONG QIODevice::readBlock ( char * data, Q_ULONG maxlen ) [pure 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 QFile, QSocket and QSocketDevice.
Q_LONG QIODevice::readLine ( char * data, Q_ULONG maxlen ) [virtual]
Reads a line of text, (or up to maxlen bytes if a newline isn't
encountered) plus a terminating \0 into data. If there is a
newline at the end if the line, it is not stripped.
Returns the number of bytes read including the terminating \0, 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().
Examples: network/clientserver/client/client.cpp, network/httpd/httpd.cpp, network/mail/smtp.cpp and network/networkprotocol/nntp.cpp.
Reimplemented in QFile.
bool QIODevice::reset ()
Sets the device index position to 0.
See also at().
void QIODevice::resetStatus ()
Sets the I/O device status to IO_Ok.
See also status().
Offset QIODevice::size () const [pure virtual]
Virtual function that returns the size of the I/O device.
See also at().
Reimplemented in QFile and QSocket.
int QIODevice::state () const
Returns bits OR'ed together that specify the current state.
The flags are: IO_Open.
Subclasses may define additional 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
find out the reason why the operation did not succeed.
The status codes are:
See also resetStatus().
int QIODevice::ungetch ( int ch ) [pure virtual]
Puts the character ch back into the I/O device and decrements the
index position if it is not zero.
This function is normally called to "undo" a getch() operation.
Returns ch, or -1 if an error occurred.
This virtual function must be reimplemented by all subclasses.
See also getch() and putch().
Reimplemented in QFile and QSocket.
Q_LONG QIODevice::writeBlock ( const char * data, Q_ULONG len ) [pure virtual]
Writes len bytes from data 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, QSocket and QSocketDevice.
Q_LONG QIODevice::writeBlock ( const QByteArray & data )
This is an overloaded member function, provided for convenience. It behaves essentially like the above function.
This convenience function is the same as calling
writeBlock( data.data(), data.size() ).
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