QIODevice Class Reference

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

#include <qiodevice.h>

Inheritance diagram for QIODevice:

Public Member Functions
	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 uint	size () const =0
virtual int	at () const
virtual bool	at (int)
virtual bool	atEnd () const
bool	reset ()
virtual int	readBlock (char *data, uint maxlen)=0
virtual int	writeBlock (const char *data, uint len)=0
virtual int	readLine (char *data, uint maxlen)
int	writeBlock (const QByteArray &data)
QByteArray	readAll ()
virtual int	getch ()=0
virtual int	putch (int)=0
virtual int	ungetch (int)=0

Protected Member Functions
void	setFlags (int f)
void	setType (int)
void	setMode (int)
void	setState (int)
void	setStatus (int)

Protected Attributes
int	ioIndex

Private Member Functions
	QIODevice (const QIODevice &)
QIODevice &	operator= (const QIODevice &)

Private Attributes
int	ioMode
int	ioSt

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 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.

• 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:
    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, QTextStream

Definition at line 88 of file qiodevice.h.

Constructor & Destructor Documentation

QIODevice::QIODevice

(

)

Constructs an I/O device.

Definition at line 179 of file qiodevice.cpp.

{
    ioMode = 0;                                 // initial mode
    ioSt = IO_Ok;
    ioIndex = 0;
}

QIODevice::~QIODevice ( )

virtual

Destructs the I/O device.

Definition at line 190 of file qiodevice.cpp.

{
}

QIODevice::QIODevice ( const QIODevice &  )

private

Member Function Documentation

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 QStringBuffer, QFile, QBuffer, and QGStringBuffer.

Definition at line 471 of file qiodevice.cpp.

{
    return ioIndex;
}

bool QIODevice::at ( int  pos )

virtual

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

See also

size()

Reimplemented in QStringBuffer, QFile, QBuffer, and QGStringBuffer.

Definition at line 481 of file qiodevice.cpp.

{
#if defined(CHECK_RANGE)
    if ( (uint)pos > size() ) {
        qWarning( "QIODevice::at: Index %d out of range", pos );
        return FALSE;
    }
#endif
    ioIndex = pos;
    return TRUE;
}

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.

Definition at line 498 of file qiodevice.cpp.

{
    if ( isSequentialAccess() || isTranslated() ) {
        QIODevice* that = (QIODevice*)this;
        int c = that->getch();
        bool result = c < 0;
        that->ungetch(c);
        return result;
    } else {
        return at() == (int)size();
    }
}

void QIODevice::close ( )

pure virtual

Closes the I/O device.

This virtual function must be reimplemented by all subclasses.

See also

open()

Implemented in QStringBuffer, QFile, QBuffer, and QGStringBuffer.

int QIODevice::flags ( ) const

inline

Returns the current I/O device flags setting.

Flags consists of mode flags and state flags.

See also

mode(), state()

Definition at line 94 of file qiodevice.h.

{ return ioMode; }

void QIODevice::flush ( )

pure virtual

Flushes an open I/O device.

This virtual function must be reimplemented by all subclasses.

Implemented in QStringBuffer, QFile, QBuffer, and QGStringBuffer.

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(), ungetch()

Implemented in QStringBuffer, QFile, QBuffer, and QGStringBuffer.

bool QIODevice::isAsynchronous ( ) const

inline

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

This mode is currently not in use.

See also

isSynchronous()

Definition at line 104 of file qiodevice.h.

{ return ((ioMode & IO_Async)      == IO_Async); }

bool QIODevice::isBuffered ( ) const

inline

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

See also

isRaw()

Definition at line 101 of file qiodevice.h.

{ return ((ioMode & IO_Raw)        != IO_Raw); }

bool QIODevice::isCombinedAccess ( ) const

inline

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.

Definition at line 100 of file qiodevice.h.

{ return ((ioMode & IO_Combined)   == IO_Combined); }

bool QIODevice::isDirectAccess ( ) const

inline

Returns TRUE if the I/O device is a direct access (not sequential) device, otherwise FALSE.

See also

isSequentialAccess()

Definition at line 98 of file qiodevice.h.

{ return ((ioMode & IO_Direct)     == IO_Direct); }

bool QIODevice::isInactive ( ) const

inline

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

See also

isOpen()

Definition at line 109 of file qiodevice.h.

{ return state() == 0; }

bool QIODevice::isOpen ( ) const

inline

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

See also

isInactive()

Definition at line 110 of file qiodevice.h.

{ return state() == IO_Open; }

bool QIODevice::isRaw ( ) const

inline

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

See also

isBuffered()

Definition at line 102 of file qiodevice.h.

{ return ((ioMode & IO_Raw)        == IO_Raw); }

bool QIODevice::isReadable ( ) const

inline

Returns TRUE if the I/O device was opened using IO_ReadOnly or IO_ReadWrite mode.

See also

isWritable(), isReadWrite()

Definition at line 106 of file qiodevice.h.

{ return ((ioMode & IO_ReadOnly)   == IO_ReadOnly); }

bool QIODevice::isReadWrite ( ) const

inline

Returns TRUE if the I/O device was opened using IO_ReadWrite mode.

See also

isReadable(), isWritable()

Definition at line 108 of file qiodevice.h.

{ return ((ioMode & IO_ReadWrite)  == IO_ReadWrite); }

bool QIODevice::isSequentialAccess ( ) const

inline

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()

Definition at line 99 of file qiodevice.h.

{ return ((ioMode & IO_Sequential) == IO_Sequential); }

bool QIODevice::isSynchronous ( ) const

inline

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

See also

isAsynchronous()

Definition at line 103 of file qiodevice.h.

{ return ((ioMode & IO_Async)      != IO_Async); }

bool QIODevice::isTranslated ( ) const

inline

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.

Definition at line 105 of file qiodevice.h.

{ return ((ioMode & IO_Translate)  == IO_Translate); }

bool QIODevice::isWritable ( ) const

inline

Returns TRUE if the I/O device was opened using IO_WriteOnly or IO_ReadWrite mode.

See also

isReadable(), isReadWrite()

Definition at line 107 of file qiodevice.h.

{ return ((ioMode & IO_WriteOnly)  == IO_WriteOnly); }

int QIODevice::mode ( ) const

inline

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.

Definition at line 95 of file qiodevice.h.

{ return ioMode & IO_ModeMask; }

bool QIODevice::open ( int  mode )

pure 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.

See also

close()

Implemented in QStringBuffer, QFile, QBuffer, and QGStringBuffer.

QIODevice& QIODevice::operator= ( const QIODevice &  )

private

int QIODevice::putch ( int  ch )

pure 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(), ungetch()

Implemented in QStringBuffer, QFile, QBuffer, and QGStringBuffer.

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()

Definition at line 535 of file qiodevice.cpp.

{
    int n = size()-at();
    QByteArray ba(size()-at());
    char* c = ba.data();
    while ( n ) {
        int r = readBlock( c, n );
        if ( r < 0 )
            return QByteArray();
        n -= r;
        c += r;
    }
    return ba;
}

int QIODevice::readBlock ( char *  data, uint  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()

Implemented in QStringBuffer, QFile, QBuffer, and QGStringBuffer.

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(), QTextStream::readLine()

Reimplemented in QFile, and QBuffer.

Definition at line 581 of file qiodevice.cpp.

{
    if ( maxlen == 0 )                          // application bug?
        return 0;
    int pos = at();                             // get current position
    int s  = (int)size();                       // size of I/O device
    char *p = data;
    if ( pos >= s )
        return 0;
    while ( pos++ < s && --maxlen ) {           // read one byte at a time
        readBlock( p, 1 );
        if ( *p++ == '\n' )                     // end of line
            break;
    }
    *p++ = '\0';
    return (int)((intptr_t)p - (intptr_t)data);
}

bool QIODevice::reset ( )

inline

Sets the device index to 0.

See also

at()

Definition at line 123 of file qiodevice.h.

{ return at(0); }

void QIODevice::resetStatus ( )

inline

Sets the I/O device status to IO_Ok.

See also

status()

Definition at line 113 of file qiodevice.h.

{ ioSt = IO_Ok; }

void QIODevice::setFlags ( int  f )

inlineprotected

Definition at line 136 of file qiodevice.h.

{ ioMode = f; }

void QIODevice::setMode ( int  m )

protected

Definition at line 378 of file qiodevice.cpp.

{
#if defined(CHECK_RANGE)
    if ( (m & IO_ModeMask) != m )
        qWarning( "QIODevice::setMode: Specified mode out of range" );
#endif
    ioMode &= ~IO_ModeMask;                     // reset mode bits
    ioMode |= m;
}

void QIODevice::setState ( int  s )

protected

Definition at line 393 of file qiodevice.cpp.

{
#if defined(CHECK_RANGE)
    if ( ((uint)s & IO_StateMask) != (uint)s )
        qWarning( "QIODevice::setState: Specified state out of range" );
#endif
    ioMode &= ~IO_StateMask;                    // reset state bits
    ioMode |= (uint)s;
}

void QIODevice::setStatus ( int  s )

protected

Definition at line 408 of file qiodevice.cpp.

{
    ioSt = s;
}

void QIODevice::setType ( int  t )

protected

Definition at line 363 of file qiodevice.cpp.

{
#if defined(CHECK_RANGE)
    if ( (t & IO_TypeMask) != t )
        qWarning( "QIODevice::setType: Specified type out of range" );
#endif
    ioMode &= ~IO_TypeMask;                     // reset type bits
    ioMode |= t;
}

uint QIODevice::size ( ) const

pure virtual

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

See also

at()

Implemented in QStringBuffer, QFile, QBuffer, and QGStringBuffer.

int QIODevice::state ( ) const

inline

Returns bits OR'ed together that specify the current state.

The flags are: IO_Open.

Subclasses may define more flags.

Definition at line 96 of file qiodevice.h.

{ return ioMode & IO_StateMask; }

int QIODevice::status ( ) const

inline

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()

Definition at line 112 of file qiodevice.h.

{ return ioSt; }

int QIODevice::ungetch ( int  ch )

pure 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(), putch()

Implemented in QStringBuffer, QFile, QBuffer, and QGStringBuffer.

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

pure 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()

Implemented in QStringBuffer, QFile, QBuffer, and QGStringBuffer.

int QIODevice::writeBlock

(

const QByteArray &

data

)

This convenience function is the same as calling writeBlock( data.data(), data.size() ).

Definition at line 564 of file qiodevice.cpp.

{
    return writeBlock( data.data(), data.size() );
}

Member Data Documentation

int QIODevice::ioIndex

protected

Definition at line 141 of file qiodevice.h.

int QIODevice::ioMode

private

Definition at line 144 of file qiodevice.h.

int QIODevice::ioSt

private

Definition at line 145 of file qiodevice.h.

---

The documentation for this class was generated from the following files:

• doxygen-1.8.11/qtools/qiodevice.h
• doxygen-1.8.11/qtools/qiodevice.cpp