QIODevice Class Reference

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

#include <qiodevice.h>

Inherited by QBuffer and QFile.

List of all member functions.

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 len )
virtual int writeBlock ( const char * data, uint len )
virtual int readLine ( char * data, uint maxlen )
virtual int getch ()
virtual int putch ( int )
virtual int ungetch ( int )

Protected Members

void setFlags ( int f )
void setType ( int )
void setMode ( int )
void setState ( int )
void setStatus ( int )

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 write bytes to. The QIODevice class itself is not capable of reading or writing any data; it has virtual functions for doing so. These functions are implemented by the subclasses QFile and QBuffer.

There are two types of I/O devices; <em>direct access</em> and <em>sequential access </em> devices. Files can normally be accessed directly, except stdin etc., which must be processed sequentially. Buffers are always direct access devices.

The access mode of an I/O device can be either raw or buffered. QFile objects can be created using one of these. Raw access mode is more low level, while buffered access use smart buffering techniques. The raw access mode is best when I/O is block-operated using 4kB block size or greater. Buffered access works better when reading small portions of data at a time.

An I/O device operation can be executed in either synchronous or asynchronous mode. The I/O devices currently supported by Qt only execute synchronously.

The QDataStream and QTextStream provide binary and text operations on QIODevice objects.

QIODevice provides numerous pure virtual functions you need to implement when subclassing it. Here is a skeleton subclass:

    class YourDevice : public QIODevice
    {
    public:
        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 len );
        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. a tape device).

Member Function Documentation

QIODevice::QIODevice ()

Constructs an I/O device.

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

Destroys the I/O device.

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

Virtual function that sets the I/O device index to pos.

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.

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.

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

Flushes an open I/O device.

This virtual function must be reimplemented by all subclasses.

Reimplemented in QBuffer and QFile.

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.

bool QIODevice::isAsynchronous () const

Returns TRUE if the I/O device is a asynchronous device, otherwise FALSE.

This mode is currently not in use.

bool QIODevice::isBuffered () const

Returns TRUE if the I/O device is a buffered (not raw) device, otherwise FALSE.

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.

bool QIODevice::isInactive () const

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

bool QIODevice::isOpen () const

Returns TRUE if the I/O device state has been opened, otherwise FALSE.

bool QIODevice::isRaw () const

Returns TRUE if the I/O device is a raw (not buffered) device, otherwise FALSE.

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.

bool QIODevice::isSynchronous () const

Returns TRUE if the I/O device is a synchronous device, otherwise FALSE.

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. Cannot be combined with IO_Raw.

This virtual function must be reimplemented by all subclasses.

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.

int QIODevice::readBlock ( char * data, uint len ) `[virtual]`

Reads at most len 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.

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 QBuffer and QFile.

bool QIODevice::reset ()

Sets the device index to 0.

void QIODevice::resetStatus ()

Sets the I/O device status to IO_Ok.

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.

uint QIODevice::size () const `[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 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.

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.

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.

QIODevice Class Reference

Public Members

Protected Members

Detailed Description

Member Function Documentation

QIODevice::QIODevice ()

QIODevice::~QIODevice () [virtual]

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

int QIODevice::at () const [virtual]

bool QIODevice::atEnd () const [virtual]

void QIODevice::close () [virtual]

int QIODevice::flags () const

void QIODevice::flush () [virtual]

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

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

int QIODevice::readBlock ( char * data, uint len ) [virtual]

int QIODevice::readLine ( char * data, uint maxlen ) [virtual]

bool QIODevice::reset ()

void QIODevice::resetStatus ()

void QIODevice::setFlags ( int f ) [protected]

void QIODevice::setMode ( int m ) [protected]

void QIODevice::setState ( int s ) [protected]

void QIODevice::setStatus ( int s ) [protected]

void QIODevice::setType ( int t ) [protected]

uint QIODevice::size () const [virtual]

int QIODevice::state () const

int QIODevice::status () const

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

int QIODevice::writeBlock ( const char * data, uint len ) [virtual]

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

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

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

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

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

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

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

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

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

int QIODevice::readBlock ( char * data, uint len ) `[virtual]`

int QIODevice::readLine ( char * data, uint maxlen ) `[virtual]`

void QIODevice::setFlags ( int f ) `[protected]`

void QIODevice::setMode ( int m ) `[protected]`

void QIODevice::setState ( int s ) `[protected]`

void QIODevice::setStatus ( int s ) `[protected]`

void QIODevice::setType ( int t ) `[protected]`

uint QIODevice::size () const `[virtual]`

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

int QIODevice::writeBlock ( const char * data, uint len ) `[virtual]`