QIODevice Class Reference

The QIODevice class is the base class of I/O devices. More...

All the functions in this class are reentrant when Qt is built with thread support.

#include <qiodevice.h>

Inherited by QBuffer, QFile, QSocket, and QSocketDevice.

List of all member functions.

Public Members

typedef Q_ULONG Offset
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 ) = 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
bool reset ()
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 )
Q_LONG writeBlock ( const QByteArray & data )
virtual QByteArray readAll ()
virtual int getch () = 0
virtual int putch ( int ch ) = 0
virtual int ungetch ( 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 use 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 mode argument.
close() closes the device and tidies up (e.g. flushes buffered data)
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 if given an offset.
atEnd() indicates whether there is more to read, if this is meaningful 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 sure to need and some that you will probably 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.

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.

bool QIODevice::at ( Offset pos ) `[virtual]`

Virtual function that sets the I/O device position to pos. Returns TRUE if the position was successfully set, i.e. pos is within range; otherwise returns FALSE.

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.

int QIODevice::flags () const

Returns the current I/O device flags setting.

Flags consists of mode flags and state flags.

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.

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.

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.

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.

bool QIODevice::isInactive () const

Returns TRUE if the I/O device state is 0, i.e. the device is not open; otherwise returns FALSE.

bool QIODevice::isOpen () const

Returns TRUE if the I/O device has been opened; otherwise returns FALSE.

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.

bool QIODevice::isReadWrite () const

Returns TRUE if the I/O device was opened using IO_ReadWrite mode; otherwise returns FALSE.

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.

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.

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.

Mode flags	Meaning
IO_Raw	specifies 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.

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.

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 function should return -1 if a fatal error occurs and should return 0 if there are no bytes to read.

The device must be opened for reading, and data must not be 0.

This virtual function must be reimplemented by all subclasses.

See also writeBlock(), isOpen(), and isReadable().

Reimplemented in 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 if an error occurred.

This virtual function can be reimplemented much more efficiently by the most subclasses.

See also readBlock() and QTextStream::readLine().

Reimplemented in QFile.

bool QIODevice::reset ()

Sets the device index position to 0.

void QIODevice::resetStatus ()

Sets the I/O device status to IO_Ok.

Offset QIODevice::size () const `[pure virtual]`

Virtual function that returns the size of the I/O device.

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 failed.

The status codes are:

Status code	Meaning
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_UnspecifiedError	An unspecified error happened on close.

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.

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 function should return -1 if a fatal error occurs.

This virtual function must be reimplemented by all subclasses.

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() ).

Trademarks

Qt version 3.2.0b2

QIODevice Class Reference

Public Members

Detailed Description

Member Type Documentation

QIODevice::Offset

Member Function Documentation

QIODevice::QIODevice ()

QIODevice::~QIODevice () [virtual]

Offset QIODevice::at () const [virtual]

bool QIODevice::at ( Offset pos ) [virtual]

bool QIODevice::atEnd () const [virtual]

void QIODevice::close () [pure virtual]

int QIODevice::flags () const

void QIODevice::flush () [pure virtual]

int QIODevice::getch () [pure virtual]

bool QIODevice::isAsynchronous () const

bool QIODevice::isBuffered () const

bool QIODevice::isCombinedAccess () const

bool QIODevice::isDirectAccess () const

bool QIODevice::isInactive () const

bool QIODevice::isOpen () const

bool QIODevice::isRaw () const

bool QIODevice::isReadWrite () const

bool QIODevice::isReadable () const

bool QIODevice::isSequentialAccess () const

bool QIODevice::isSynchronous () const

bool QIODevice::isTranslated () const

bool QIODevice::isWritable () const

int QIODevice::mode () const

bool QIODevice::open ( int mode ) [pure virtual]

int QIODevice::putch ( int ch ) [pure virtual]

QByteArray QIODevice::readAll () [virtual]

Q_LONG QIODevice::readBlock ( char * data, Q_ULONG maxlen ) [pure virtual]

Q_LONG QIODevice::readLine ( char * data, Q_ULONG maxlen ) [virtual]

bool QIODevice::reset ()

void QIODevice::resetStatus ()

Offset QIODevice::size () const [pure virtual]

int QIODevice::state () const

int QIODevice::status () const

int QIODevice::ungetch ( int ch ) [pure virtual]

Q_LONG QIODevice::writeBlock ( const char * data, Q_ULONG len ) [pure virtual]

Q_LONG QIODevice::writeBlock ( const QByteArray & data )

QIODevice::~QIODevice () `[virtual]`

Offset QIODevice::at () const `[virtual]`

bool QIODevice::at ( Offset pos ) `[virtual]`

bool QIODevice::atEnd () const `[virtual]`

void QIODevice::close () `[pure virtual]`

void QIODevice::flush () `[pure virtual]`

int QIODevice::getch () `[pure virtual]`

bool QIODevice::open ( int mode ) `[pure virtual]`

int QIODevice::putch ( int ch ) `[pure virtual]`

QByteArray QIODevice::readAll () `[virtual]`

Q_LONG QIODevice::readBlock ( char * data, Q_ULONG maxlen ) `[pure virtual]`

Q_LONG QIODevice::readLine ( char * data, Q_ULONG maxlen ) `[virtual]`

Offset QIODevice::size () const `[pure virtual]`

int QIODevice::ungetch ( int ch ) `[pure virtual]`

Q_LONG QIODevice::writeBlock ( const char * data, Q_ULONG len ) `[pure virtual]`